UNIVERSIDAD NACIONAL DE INGENIERÍA
FACULTAD DE INGENIERÍA QUÍMICA Y TEXTIL
“LIMPIEZA Y PREPARACIÓN SUPERFICIAL DEL ACERO POR
CHORRO DE AGUA (Waterjetting)”
INFORME DE SUFICIENCIA
PARA OPTAR EL TÍTULO PROFESIONAL DE:
INGENIERO QUÍMICO
POR LA MODALIDAD DE ACTUALIZACIÓN DE CONOCIMIENTOS
PRESENTADO POR:
DWIGHT HUGO VILELA ZELADA
LIMA – PERÚ
2015
AGRADECIMIENTO Y
DEDICATORIA
Agradezco a todas las personas que de una u otra forma estuvieron conmigo, porque
cada una aportó con un granito de arena; y es por ello que a todos y cada uno de
ustedes les dedico todo el esfuerzo, sacrificio y tiempo que entregué a esta tesis.
A tí Dios, por darme la oportunidad de existir así, aquí y ahora; por mi vida, que la
he vivido junto a ti. Gracias por iluminarme y darme fuerzas y caminar por tu
sendero.
A ti Gordito, por tu incondicional apoyo, tanto al inicio como al final de mi carrera;
por estar pendiente de mí a cada momento.
Gracias Pa’ por ser ejemplo de arduo trabajo y tenaz lucha en la vida.
A ti Ma´, que tienes algo de Dios por la inmensidad de tu amor,
y mucho de ángel por ser mi guarda y por tus incansables cuidados.
Porque si hay alguien que está detrás de todo este trabajo,
eres tú mi Ñañi, que has sido, eres y serás el pilar de mi vida.
A ti Guido, porque juntos aprendimos a vivir,
crecimos como cómplices día a día y somos amigos incondicionales de toda la vida,
compartiendo triunfos y fracasos. Doy gracias a Dios porque somos hermanos.
A mi familia, ustedes queridos abuelitos, tíos y primos,
porque de una u otra forma, con su apoyo moral me han incentivado a seguir
adelante, a lo largo de toda mi vida.
A todos, mis amigos y amigas que me han brindado desinteresadamente su valiosa
amistad, entre ellos a mis padrinos; gracias por ser la sal que condimenta mi vida.
A la UNI, y a mis estimados maestros, que, a lo largo de mi carrera, me han
transmitido sus amplios conocimientos y sus sabios consejos; especialmente a los
Ingenieros Aldo Delgado, Pedro Pizarro y Mario Garayar, quienes, muy
acertadamente, dirigieron mi Informe de Suficiencia.
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RESUMEN
La vida de cualquier sistema de recubrimientos en un sustrato de acero depende
mucho de la calidad de la preparación de la superficie. Las soldaduras lisas, bordes
redondeados y las superficies limpias, todos contribuyen a la vida de servicio de los
recubrimientos aplicados. El propósito de este trabajo está dirigido en mostrar el
desarrollo del método de preparación superficial del acero para la aplicación de
recubrimientos usando chorro de agua como ingrediente principal de limpieza.
Con esta propuesta se busca reemplazar el abrasivo utilizado, en la preparación
superficial del acero por el método de limpieza abrasiva seca, dado que las partículas
abrasivas y el polvo circundante generado (arena, escoria de cobre, granalla, etc) en
ciertas industrias era considerado una molestia o un peligro para sus operaciones ya
que pueden dañar los equipos de procesos, los instrumentos y dispositivos de
medición, atrapar contaminantes en la superficie del acero que se está limpiando y
contaminar el ambiente así como también ser perjudicial para la salud del operador.
La metodología desarrollada en este trabajo consiste en preparar la superficie de
acero del casco externo de tanques de almacenamiento en servicio previamente
pintados como parte de las operaciones de recubrimientos para mantenimiento
mediante un chorro de agua tipo UHP haciendo uso del equipo manual y de la
normativa vigente que rige dicha preparación. Se demostrara que desarrollando el
método de limpieza, el sistema de recubrimientos tendrá el performance esperado.
Finalmente, se expondrán las conclusiones referentes al trabajo realizado
en cuanto a la limpieza y preparación superficial del acero por chorro de
agua y las recomendaciones para mantener el sistema funcionando y en
concordancia a los requisitos de la normatividad vigente.
CONTENIDO
I. INTRODUCCIÓN…………………………………………………………… 11
II. MARCO TEÓRICO…………………………………………………………. 13
2.1.Corrosión y control de la corrosión………………………………………. 13
2.1.1. La corrosión como un proceso electroquímico……………........... 14
2.1.2. La celda de corrosión…………………………………………….. 15
2.1.3. Corrosión en estructuras de acero…………………………........... 17
2.1.4. Calamina..……………………………………………………….... 19
2.1.5. Serie galvánica……………………………………………………. 20
2.1.6. Influencias del ambiente de servicio y la corrosión…..…………… 24
2.2.Tipos de corrosión…………………………………………....................... 27
2.2.1. Corrosión generalizada……………………………………………. 27
2.2.2. Corrosión localizada………………………………………………. 27
2.2.3. Importancia de la corrosión……………………………………….. 30
2.3.Efectos de la corrosión……………………………………………………. 31
2.3.1. Efectos en la seguridad……………………………………………. 31
2.3.2. Efectos en el costo………………………………………………… 32
2.3.3. Efectos en la apariencia…………………………………………… 33
2.4.Control de la corrosión……………………………………………………. 33
2.4.1. Control de la corrosión mediante el método de diseño……..…….. 33
2.4.2. Control de la corrosión mediante el uso de inhibidores…………… 34
2.4.3. Control de la corrosión mediante la selección de materiales……… 34
2.4.4. Control de la corrosión mediante sistemas de protección catódica.. 35
2.4.5. Control de la corrosión mediante sistemas de recubrimientos
protectores…………………………………………………………. 35
2.4.6. Control de la corrosión mediante alteraciones del ambiente……… 36
2.5.Programas de control de la corrosión……………………………………… 37
2.6.Preparación de la superficie……………………………………………….. 37
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2.6.1. Superficies de acero……………………………………………….. 38
2.6.2. Limpieza previa…………………………………………………… 39
2.6.3. Sales solubles……………………………………………………… 40
2.6.4. Limpieza con herramientas manuales……………………………... 41
2.6.5. Limpieza con herramientas de poder……………………………… 42
2.6.6. Limpieza abrasiva………………………………………………… 44
2.6.7. Chorro de agua (Waterjetting)…………………………………….. 48
2.7.Sistema de recubrimientos………………………………………………… 59
2.7.1. Sistemas de una capa……………………………………………… 59
2.7.2. Sistemas de recubrimientos multicapa……………………………. 60
2.7.3. compatibilidad……………………………………………………. 60
2.8.Defectos de recubrimientos……………………………………………….. 61
2.8.1. Película que no seca (falta de curado)……………………………. 61
2.8.2. Exudación de amina………………………………………………. 61
2.8.3. Escurrimiento, colgamiento, cortinas, arrugas……………………. 62
2.8.4. Discontinuidades, saltos, holidays, áreas desnudas………………. 63
2.8.5. Caleamiento……………………………………………………….. 63
2.8.6. Formación de cráteres…………………………………………….. 64
2.8.7. Puntos de alfiler…………………………………………………… 65
2.8.8. Ampollamiento……………………………………………………. 65
2.8.9. Agrietamiento (cuarteamiento) y desprendimiento……………….. 66
2.8.10. Fallas de adhesión: en cáscara, delaminación y
desprendimiento…………………………………………………… 67
2.8.11. Fallas en soldaduras y bordes……………………………………... 68
2.8.12. Muescas o puntos astillados………………………………………. 70
2.9.Pruebas de inspección……………………………………………………... 70
2.9.1. Condiciones ambientales………………………………………….. 70
2.9.2. Preparación de la superficie………………………………………. 71
2.9.3. Sales solubles……………………………………………………… 72
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2.9.4. Medición de espesores de película seca…………………………… 73
2.9.5. Adherencia de recubrimientos……………………………………... 74
2.9.6. Discontinuidades (holidays)……………………………………….. 74
2.10. Mantenimiento de sustratos en servicio..………………………….. 75
2.10.1. Operaciones de recubrimientos para mantenimiento……………… 75
2.10.2. Elementos de las operaciones de recubrimientos para
mantenimiento…………………………………………………….. 76
III. LIMPIEZA Y PREPARACIÓN SUPERFICIAL DEL ACERO MEDIANTE
CHORRO DE AGUA (WATERJETTING)...………………………………… 78
3.1.Especificaciones para las operaciones de recubrimientos para
mantenimiento…………………………………………………………….. 78
3.1.1. Procedimiento de trabajo para las operaciones de mantenimiento... 79
3.2.Pintado de mantenimiento con preparación Waterjetting UHP…..………. 87
3.2.1. Aspectos previos….…………………………………………..…... 88
3.2.2. Normas y equipos usados…………………………………………. 90
3.2.3. Preparación de superficie y sistema de pintado…………………... 92
3.2.4. Resultados y discusiones………………………………………….. 94
IV. CONCLUSIONES Y RECOMENDACIONES…………………………….. 104
4.1.CONCLUSIONES………………………………….................................. 104
4.2.RECOMENDACIONES………………………………………………… 104
V. BIBLIOGRAFÍA.……………………………………………………............. 106
VI. ANEXOS…………………………………………………………………….. 107
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LISTA DE FIGURAS
Figura 1: Representación esquemática del mecanismo de corrosión………............ 15
Figura 2: Celda de corrosión………………………………………………………. 16
Figura 3: Corrosión en estructuras de acero……………………………………….. 19
Figura 4: La cascarilla de laminación no protege al acero………………………… 20
Figura 5: Ambiente químico/marino – plataforma marina……..………………… 24
Figura 6: Ambiente químico con alta humedad – refinería……………………….. 25
Figura 7: Ambiente marino con alta humedad…………………...……………….. 26
Figura 8: Ambiente químico con baja humedad – planta de generación de
poder………………………………………………………………………………. 26
Figura 9: Ambiente rural – Puente vehicular………………………………….…... 27
Figura 10: Corrosión generalizada…………………...……………………………. 28
Figura 11: Corrosión por picadura……………………………………...…………. 29
Figura 12: Corrosión en cavidades………………………………………………… 30
Figura 13: Plataforma oxidado en puente interconector de tanques……..……...… 31
Figura 14: Efectos de la corrosión – apariencia………………………………..….. 33
Figura 15: Equipo de DH fuera de un tanque……………………………………… 36
Figura 16: Acero nuevo……………………………………………………………. 38
Figura 17: Acero con recubrimiento existente…………………………………….. 39
Figura 18: Limpieza previa………………………………………………………… 40
Figura 19: Limpieza con herramientas manuales……………………...…………... 42
Figura 20: Limpieza con herramientas de poder………………………...………... 43
Figura 21: Limpieza abrasiva seca………………………....................................... 45
Figura 22: Chorro de agua……………………………………………………......... 49
Figura 23: No oxidada………………….…………………………………............. 55
Figura 24: Flash rust ligero (L)………………………………………...………….. 56
Figura 25: Flash rust moderado (M)……………………………………………….. 57
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Figura 26: Flash rust pesado (H)……………………...…………………………... 57
Figura 27: Recubrimiento sin curar………………………………………………... 62
Figura 28: Exudación de amina……………………...…………………………….. 62
Figura 29: Escurrimiento…………………………………………………………... 63
Figura 30: Holidays……………………………………………………………….. 64
Figura 31: Caleamiento………………………...…………………………………. 64
Figura 32: Cráteres………………………...………………………………………. 65
Figura 33: Pinholes o puntos de alfiler……………………………...……………... 66
Figura 34: Ampollamiento……………………...…………………………............ 67
Figura 35: Cuarteamiento………………………...………………………………. 67
Figura 36: Fallas de adhesión……………………………………………………… 68
Figura 37: Bordes………………………...……………………………………….. 69
Figura 38: Termómetro de superficie……………………………...……………… 70
Figura 39: Psicrómetro giratorio……………………………...…………………… 71
Figura 40: Determinación del perfil de anclaje mediante cinta réplica…....……... 72
Figura 41: Extracción de las sales solubles sobre la superficie preparada
mediante parche bresle……………………………………………………….....… 73
Figura 42: Medición de espesores de película seca (medidor tipo II)……….......... 73
Figura 43: Determinación de la adherencia mediante Dolly Pull-Off……...…….. 74
Figura 44: Detección de discontinuidades mediante equipo de bajo voltaje DC… 75
Figura 45: Tanque de almacenamiento de dióxido de carbono (CO2)…………..... 76
Figura 46: Unidad típica de chorro de agua…………………………….…............ 80
Figura 47: Unidad de chorro de agua robótica………………….…………............ 81
Figura 48: Valor de conductividad de sales solubles en el agua utilizada……….... 94
Figura 49: Medición del perfil de anclaje……………………………………….… 95
Figura 50: Valor del perfil de anclaje mediante micrómetro……………….……… 95
Figura 51: Remoción de contaminantes superficiales mediante lavado……………96
Figura 52: Limpieza superficial mediante chorro de agua ( Waterjetting)…….….. 98
Figura 53: Flash Rust sobre la superficie limpiada………. ………………………. 98
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Figura 54: Extracción de las sales solubles método del parche de látex…..….…... 99
Figura 55: Valor de la conductividad de las sales solubles en agua……………… 99
Figura 56: Valor de la presión de ruptura en Psi……………………...…............. 103
LISTA DE TABLAS
Tabla 1: Tipos de waterjetting………………………………………......………… 83
Tabla 2: Grados de limpieza para el waterjetting…………………………………. 84
Tabla 3: Grado del flash rust después del retiro de la 10ma
cinta………………… 86
Tabla 4: Característica de los Tanques de Almacenamiento………………………. 88
Tabla 5: Grado de preparación de superficie……………………………………… 93
Tabla 6: Sistema de pintado…………………………...………………………...… 93
Tabla 7: Resumen de condiciones ambientales…………………………………..... 96
Tabla 8: Pruebas de adhesión por tracción…………………………………...…… 102
I. INTRODUCCIÓN
La limpieza con abrasivo en seco es uno de los métodos más usados en la preparación
de la superficie debido a que es rápido y barato; y muchos usuarios de recubrimientos
quieren ver un grabado definido o perfil superficial definido.
Inicialmente, las normas para la preparación de la superficie fueron escritas, y los
estándares visuales adoptados, basándose en la arena como el abrasivo. Normas
visuales auxiliares han sido basadas en el uso de otros no-metálicos, como el granate,
escorias de cobre, níquel o carbón, o arena de olivino y los metálicos, incluyendo los
perdigones de acero, granalla de acero, o una combinación de los ambos.
Existen algunos problemas asociados con la limpieza con abrasivo en seco. En el caso
de la arena, causa problemas de salud como silicosis por la respiración de la sílica.
En general cuando limpiando con abrasivos, las partículas de abrasivo volantes y el
polvo circundante pueden dañar al equipo giratorio sensible y bloquear filtros,
dañando instrumentos y dispositivos de medición, o contaminando el ambiente; así
como también puede atrapar contaminantes en la superficie del sustrato que se está
limpiando.
Las regulaciones gubernamentales actuales requieren cierto equipo de seguridad el
cual incluye respiradores para los trabajadores en aire libre cerca de una operación de
limpieza con abrasivo y, en el caso de eliminación de plomo, se requiere un
confinamiento total.
Bajo la influencia continua de las regulaciones gubernamentales, la industria de
recubrimientos está trabajando para el desarrollo de métodos para la preparación de
superficies sensibles al medioambiente y fáciles de usar. En los años más recientes, se
12
ha encontrado que el uso del chorro de agua es un método viable de preparación de
la superficie. Como resultado, NACE (Asociación Nacional de Ingenieros de
Corrosión) y SSPC (Sociedad de los Recubrimientos Protectores) de han desarrollado
y publicado una serie de normas en conjunto para preparación de superficies, SSPC-
SP WJ-1/ NACE WJ-1, Limpieza a metal desnudo; SSPC-SP WJ-2/ NACE WJ-2,
Limpieza muy exhaustiva; SSPC-SP WJ-3/ NACE WJ-3, Limpieza profunda y
SSPC-SP WJ-4/ NACE WJ-4, Limpieza ligera o superficial.
II. DESARROLLO DE LOS CONCEPTOS Y TÉCNICAS
Es esencial que el nivel de contaminantes (óxido, calamina, suciedad, sales, aceites
y/o grasas, etc) en una superficie se mida antes de la aplicación del recubrimiento,
con el fin de asegurar que se obtenga la calidad y la vida óptima del recubrimiento.
Si el recubrimiento se aplica a una superficie contaminada, que no está debidamente
preparada, podría fallar prematuramente resultando en repintados y mantenimientos
costosos.
2.1 Corrosión y control de la corrosión
La corrosión usualmente se describe por sus resultados. Todos estamos familiarizados
con los términos herrumbre, laminaciones, decoloración, oxidación, picadura, etc.
Estos términos descriptivos se enfocan en las características fácilmente visibles de los
productos de la corrosión – los resultados del proceso de corrosión. El proceso actual
de corrosión es menos visible y no fue caracterizado correctamente hasta principios
del siglo 20. Todavía se realizan investigaciones para ampliar nuestra comprensión y
prepararnos mejor en la batalla para controlar la corrosión. El conocimiento del
proceso de la corrosión es necesario para identificar y ocuparse adecuadamente de sus
efectos extensivos.
El proceso de la corrosión actúa en los materiales desarrollados, generalmente
metales. Los materiales desarrollados son aquellos que se fabrican para servir como
componentes de la infraestructura de la sociedad. Para los propósitos de esta
discusión, el acero representa el material más comúnmente utilizado en la
construcción. Por su parte, el acero está compuesto principalmente de hierro
(abreviado como Fe). El acero contiene aproximadamente 95% hierro. La corrosión
más económicamente significativa en la industria tiene que ver con el deterioro del
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hierro. Mientras que el acero contiene otros elementos adicionales al hierro, algunos
de los cuales tiene un impacto dramático en la resistencia a la corrosión.
El proceso de corrosión implica el deterioro de una sustancia, generalmente un metal,
o de sus propiedades debido a una reacción con su ambiente. Esencialmente, las
procesos de corrosión (Montaña de Energía para el Hierro) convierten el hierro dentro
del acero en otra sustancia que ya no posee las características deseadas (ej. dureza,
resistencia).
El producto más común de la corrosión es un óxido de hierro (óxido férrico o
“herrumbre”) formado al agregar oxígeno. El óxido de hierro tiene pocas
características deseables para el uso como un material desarrollado. El óxido de
hierro derivado del proceso de corrosión consume el metal. El volumen de metal (y
su espesor) eventualmente se reduce a un punto donde un componente estructural
hecho de acero no podrá realizar la función para la cual fue diseñado (ver figura 1).
2.1.1 La corrosión como un proceso electroquímico
Toda la corrosión del hierro, en condiciones ambientales normales, es un proceso
electroquímico. Simplemente esto significa que los iones y los electrones se
transfieren a través de una superficie, los que implica una generación de corriente
(corriente de corrosión).
Tanto los electrones (a través de un conductor metálico) como los iones (a través de
un electrolito) llevan la corriente de corrosión.
Mientras mayor sea el flujo de corriente en el circuito de corrosión, mayor será la
pérdida de metal.
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Figura 1 Representación esquemática del mecanismo de corrosión
Fuente: La prevención de la corrosión en estructuras metálicas por Fabio Domingos
Pannoni, Ph.D.
2.1.2 La celda de corrosión
Para que la corrosión pueda ocurrir, ciertas condiciones y elementos son esenciales.
Éstos se conocen colectivamente como la celda de corrosión e incluyen el ánodo, el
cátodo, la ruta metálica o conductor externo y el electrolito (ver figura 2).
El ánodo es esa parte del metal que se corroe, es decir, que se disuelve en el
electrolito. El metal que se disuelve lo hace en la forma de iones cargados
positivamente. Los electrones generados se conducen al cátodo. El deterioro del
metal ocurre en el ánodo. Es la parte de la celda donde el hierro metálico se convierte
en otra sustancia por primera vez. El ánodo representa la ubicación en la superficie
Ánodo: Fe Fe2+
+ 2e-
Cátodo: 1/2 O2 + ½ H2O + 2e- 2OH-
4Fe + 2H2O + 3 O2 2Fe2O3 . H2O (FeOOH)
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metálica en donde ocurre la oxidación. El metal se transforma en iones positivamente
cargado (cationes). Durante la oxidación, se genera exceso de electrones.
Figura 2 Celda de corrosión
Fuente: http://maintenancela.blogspot.com/2011/09/corrosión y su control parte I
.html
El cátodo es la región más noble en el electrodo (superficie metálica, o en el caso de
la analogía con la batería, la varilla de carbono) donde se consumen los electrones. La
reacción eléctrica continúa en el cátodo, que es positivo, lo opuesto del ánodo. La
reacción generalmente ioniza al electrolito para formar iones como el hidrógeno
(liberado como gas) e iones hidroxilos.
Éstos se combinan a menudo con el metal disuelto para formar compuestos como el
hidróxido ferroso (en el caso del hierro o el acero), reaccionando subsecuentemente
para convertirse en óxido férrico o herrumbre. Mientras que la oxidación ocurre en el
ánodo, la reducción ocurre en el cátodo. El exceso de electrones generados en el
Migración de electrones
Conexión eléctrica
Ánodo (se oxida)
Cátodo (se reduce)
Electrolito (medio)
Corriente
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ánodo se consume en el cátodo. La oxidación-reducción siempre ocurre al mismo
tiempo – no puede ocurrir sólo oxidación o reducción. El ánodo y el cátodo tienen
diversos potenciales, creándose una diferencia de “voltaje” entre ellos. Los
potenciales son una función de los estados químicos y físicos. La diferencia de
potencial es la fuerza motora para el proceso de corrosión.
La ruta metálica conecta el ánodo y el cátodo y permite el paso de electrones,
generados en el ánodo, hacia el cátodo. Cuando la corrosión ocurre en una superficie
metálica, hay siempre una ruta o pasaje metálico que une el ánodo (o áreas anódicas)
con el cátodo (o áreas catódicas). Si no hubiera ruta metálica alguna, la reacción de
corrosión no ocurriría.
Un electrolito es un medio que conduce la corriente iónica (en lugar de eléctrica). La
mayoría de los electrolitos son base agua y, en la práctica, el electrolito contiene
iones que son partículas de materia que llevan una carga positiva o negativa. Para que
las reacciones de oxidación y reducción pueden ocurrir, se requiere un camino para el
transporte de los iones (especies negativa y positivamente cargadas llamadas aniones
y cationes, respectivamente) entre el ánodo y el cátodo. El electrolito debe estar
presente para “cerrar el lazo” en la celda de corrosión.
La corriente de corrosión es llevada mediante el transporte de iones a través del
electrolito. Los aniones son atraídos al ánodo y los cationes al cátodo, donde se
pueden combinar con los productos de oxidación y reducción. El agua ambiental
costa afuera (y las sales químicas disueltas) forman el electrolito primario.
2.1.3 Corrosión en estructuras de acero
Cuando una estructura de acero se corroe, los cuatro elementos de la celda de
corrosión están presentes. El acero conduce electricidad, de modo que proporciona su
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propia ruta metálica, la cual genera muchas áreas anódicas y catódicas debido a las
diferencias de potenciales (eléctricas) y luego se corroe al estar en el contacto con un
electrolito.
Las sales químicas disueltas en el electrolito aumentan la eficacia (velocidad) de la
reacción de corrosión. Puesto que el acero no es un metal perfectamente uniforme u
homogéneo, una sola placa de acero puede tener muchas áreas anódicas y catódicas
minúsculas en su superficie, como se demuestra en Ánodos y Cátodos en la
Superficie de Acero.
Las áreas anódicas y catódicas se forman por áreas en la superficie de la lámina, y
difieren (quizás sólo ligeramente) unas de otras en su potencial eléctrico. Por
consiguiente, el acero ya tiene tres de los cuatro elementos necesarios para crear una
celda de corrosión. Las mismas condiciones existen en la mayoría de los otros
metales.
Cuando una lámina de acero desnuda se moja con el rocío o la lluvia, el agua puede
actuar como un electrolito. Si la lámina se ha expuesto a la atmósfera, es probable
que los químicos en ésta o en la superficie del metal se combinen con el agua para
formar un electrolito más eficiente sobre el sustrato (ver figura 3).
El agua pura es un electrolito muy pobre, pero si existe la presencia de sales químicas
(ej., cloruro de sodio en un ambiente marino), éstas pueden disolverse en el agua y
crear un electrolito que llega a ser más eficaz conforme aumenta la concentración de
los químicos disueltos.
La sal (cloruro de sodio) está presente en el ambiente marino, en el agua producida en
la producción de petróleo y gas y en la refinación, así como en las sales para el
descongelamiento de caminos usadas en muchas carreteras en el hemisferio norte.
19
Otras sales químicas comunes incluyen sulfatos derivados de los productos sulfurosos
de la combustión industrial.
Figura 3 Corrosión en estructuras de acero
Fuente: http://biolarioja.com.ar/Quimica/capitulos/Capitulo20
2.1.4 Calamina
La corrosión en una superficie de acero puede propiciarse por la presencia de la
calamina. La calamina puede observarse en una superficie de hierro y acero nueva en
forma de capas azul-negras de óxido ferroso, algunas de las cuales son más duras que
el metal base. La calamina es eléctricamente positiva con relación al hierro o al acero,
de modo que son catódicas con respecto al metal base. Una celda de corrosión se
establece en presencia de humedad, y la calamina catódica promueve la corrosión en
las áreas anódicas del acero desnudo (ver figura 4). La calamina es:
Una capa de hierro/óxido de hierro de color azul-negro
Catódica con respecto al sustrato
Generalmente removida ante de pintar
20
Ésta es una razón por la que es importante remover la calamina de las superficies de
acero antes de aplicar el recubrimiento. No deseamos promover la corrosión en la
superficie, o cubrir las celdas de corrosión activas con una película de pintura.
Figura 4 La cascarilla de laminación no protege al acero
Fuente: La prevención de la corrosión en estructuras metálicas por Fabio
Domingos Pannoni, Ph.D.
2.1.5. Serie galvánica
Una Serie Galvánica es una lista de materiales ubicados según el orden de sus
potenciales de corrosión, iniciando con el que se corroe más fácilmente o el más
21
Extremo anódico (activo) Magnesio
Zinc
Aluminio, Cadmio
Acero o Hierro
Plomo
Estaño
Níquel (estado activo)
Latones
Cobre
Bronces
Monel
Níquel (estado pasivo)
Titanio
Acero inoxidable (estado pasivo)
Plata
Grafito
Oro
Extremo catódico (noble) Platino
activo en la parte superior, y terminando con el que se corroe con menor facilidad o el
menos activo en la parte inferior.
Por convención, se dice que los metales más activos tienen potenciales de corrosión
negativos, y se denominan anódicos. Los metales menos activos se denominan
catódicos o nobles.
Las reglas generales de la corrosión galvánica (metales disímiles) se desglosan a
continuación:
22
Cuando se conectan metales disímiles, el metal más activo (o anódico) se corroe más
rápidamente, mientras el metal más noble (menos activo o catódico) tiende a protegerse y
se corroe menos.
La tendencia a la corrosión aumenta conforme la diferencia de potencial entre los metales
aumenta.
Factores que Afectan la Velocidad de Corrosión:
La velocidad de corrosión es determinada por una variedad de factores, algunos de
ellos bastante complicados. Sin embargo, existen cinco factores que tienen un papel
determinante en la corrosión. Estos son:
Oxígeno: Al igual que el agua, el oxígeno aumenta la velocidad de corrosión. La
corrosión puede presentarse en un ambiente con deficiencia de oxígeno, pero la
velocidad de la reacción de corrosión (y la destrucción del metal) generalmente
será mucho más lenta. En condiciones de inmersión, puede ser que el electrolito en
contacto con un área del metal contenga más oxígeno que el electrolito que está en
contacto con otras áreas. El área en contacto con la concentración más alta de
oxígeno será catódica en relación con el resto de la superficie. De esta manera se
forma una celda de concentración de oxígeno que resulta en altas velocidades de
corrosión.
Temperatura: Las reacciones de corrosión son electroquímicas en naturaleza y
generalmente se aceleran con el aumento de la temperatura; por lo tanto, la
corrosión ocurre más rápidamente en ambientes más calurosos que en los
ambientes fríos.
Sales químicas: Las sales químicas pueden servir para aumentar la velocidad de
corrosión incrementando la eficiencia (conductividad) del electrolito. La sal
23
química más común es el cloruro de sodio, un elemento importante del agua de
mar. El cloruro de sodio depositado en superficies expuestas a la atmósfera
también actúa como material higroscópico (ej., puede extraer humedad del aire), lo
que aumentará la corrosión en áreas no sumergidas.
Humedad (o Condensación): La humedad y el tiempo de condensación tienen un
papel importante en la promoción y aceleración de la velocidad de corrosión. El
tiempo de condensación se refiere al tiempo en que un sustrato expuesto a la
atmósfera mantiene suficiente humedad para apoyar el proceso de corrosión.
Cuanto más húmedo sea el ambiente, mayor probabilidad que ocurra la corrosión.
La industria de la aviación se aprovecha de este hecho cuando almacenan un avión
en el desierto sin encerrarlo en edificios con aire acondicionado. Incluso a
temperaturas elevadas, hay pocos electrolitos disponibles para la celda de
corrosión. La corrosión puede ocurrir sin agua visible, pero la velocidad disminuye
significativamente por debajo del 60% de humedad relativa aproximadamente
(para el hierro).
Contaminantes y Gases Ácidos: La lluvia ácida, los productos químicos
generados en plantas de fabricación y de procesamiento, y los cloruros en áreas
costeras promueven la corrosión. Los gases ácidos, tales como el dióxido de
carbono, pueden también disolverse en la película de humedad que está en
contacto con el metal. Además del efecto directo del ataque químico, estos
materiales reducen la resistencia eléctrica del electrolito. Reducir la resistencia en
la celda de corrosión permite mayor densidad de corriente de corrosión y, por
ende, aumenta la velocidad de corrosión. De nuevo, la corrosión es la degradación
de materiales desarrollados en contacto con un ambiente corrosivo. El ambiente
corrosivo generalmente se define por las características del electrolito. Los
24
ambientes pueden incluir la inmersión en un líquido (agua), o atmosférico, como
veremos en la siguiente sección.
2.1.6. Influencias del ambiente de servicio y la corrosión
Las influencias del ambiente afectan las velocidades de corrosión. Varios ambientes
comunes reconocidos por profesionales del control de la corrosión son:
a) Ambiente químico / marino
Este es un ambiente muy severo que causa una oxidación muy rápida. Las sales
aerotransportadas y los agentes químicos contaminantes pueden servir para estimular
la corrosión. La humedad y el agua de mar proporcionan los electrolitos, los cuales
aceleran dicho proceso.
Figura 5 Ambiente químico/marino – plataforma marina
Fuente: http://energiaslibres.wordpress.com/2012/02/03/la gran mentira sobre la
formación del petróleo, el petróleo no se formó a partir de los restos de seres vivos
acuáticos, vegetales y animales/
25
b) Ambiente químico con alta humedad
Este ambiente es altamente corrosivo, debido a los gases, los químicos y a la alta
humedad, todo lo cual puede estimular la corrosión.
Figura 6 Ambiente químico con alta humedad – refinería
Fuente: http://www.centinelaeconomico.com/2012/08/26/isaac amenaza
refinerías de EEUU y podría impulsar el precio del petróleo/
c) Ambiente marino con alta humedad
Este ambiente proporciona un electrolito activo a través de la presencia de humedad y
partículas de sal. Se sabe que la zona de salpique (generalmente definida como el
nivel medio de la marea hasta 3.6 m. sobre la marea alta sufre de corrosión
particularmente alta (ver figura 7).
d) Ambiente químico con baja humedad
La baja humedad generalmente crea un ambiente menos corrosivo que la alta
humedad; sin embargo, tanto los gases como los químicos presentes pueden estimular
la corrosión (ver figura 8).
26
Figura 7 Ambiente marino con alta humedad
Fuente: Propia
Figura 8 Ambiente químico con baja humedad – Planta de generación de poder
Fuente: http://www.electrosector.com/estiman que un cuarto de generación de
energía mundial será nuclear para 2050//
e) Ambiente rural
Este puede ser el ambiente menos corrosivo de los cinco debido a que el aire limpio
no proporciona contaminantes en el aire y no hay humedad presente para servir como
un electrolito.
27
Figura 9 Ambiente rural – Puente vehicular
Fuente: Foto Sr. Aquiles León
2.2. Tipos de corrosión
Hay dos amplias clasificaciones de la corrosión: generalizada y localizada.
2.2.1. Corrosión generalizada
La corrosión generalizada resulta en una pérdida de material relativamente uniforme
sobre la superficie entera. Generalmente, ésta acción resulta en una disminución del
espesor, de manera general, de la superficie afectada. La corrosión generalizada es
relativamente fácil de evaluar y no causa fallas catastróficas (ver figura 10).
2.2.2. Corrosión localizada
La corrosión localizada ocurre en sitios definidos de la superficie metálica. Las áreas
inmediatamente adyacentes a la corrosión localizada normalmente se corroen a un
grado menor. La corrosión localizada ocurre a menudo en las áreas que son difíciles
de evaluar. Esta forma de corrosión es menos común en ambientes de exposición
28
atmosférica que en ambientes de inmersión o salpique/rocío, y donde algunos factores
especiales están implicados, tales como la exposición prolongada al agua líquida, los
agentes contaminantes, o celdas galvánicas.
Figura 10 Corrosión generalizada
Fuente: Propia
Se generan las celdas galvánicas cuando diversos tipos de metales están en contacto
eléctrico en un electrolito común. La actividad de corrosión en sitios de corrosión
localizada puede variar con cambios como defectos en el recubrimiento, cambios en
contaminantes o agentes contaminadores y cambios en el electrolito.
Las formas predominantes de corrosión localizada en las plataformas y estructuras
marinas son las picaduras y la corrosión en cavidades.
a) Corrosión por picadura
En la corrosión por picaduras el daño no ocurre uniformemente, sino primordialmente
en zonas específicas donde se producen picaduras profundas. Los fondos de las
picaduras son ánodos en una pequeña celda de corrosión localizada, a menudo
29
agravada por una relación de área cátodo grande-ánodo pequeño. Las picaduras
pueden iniciarse en una superficie abierta, libremente expuesta o en las
imperfecciones en el recubrimiento. Las picaduras profundas, incluso las que son
completamente penetrantes, pueden desarrollarse con una cantidad relativamente
pequeña de pérdida del metal. Las picaduras pueden ser aisladas o un grupo de
picaduras puede coalescer para formar un área de daño grande. Las picaduras son
especialmente frecuentes en los metales que forman una capa protectora de óxido y
en ambientes de alta contaminación por cloruros (donde los cloruros promueven la
degradación de la capa de óxido).
Figura 11 Corrosión por picadura
Fuente: Propia
b) Corrosión en cavidades
La corrosión en cavidades ocurre en una superficie de metal que está bloqueado de la
exposición directa al medio ambiente, debido a la proximidad cercana con otro
material que forme una brecha estrecha (o cavidad) entre ellos. Las diferencias en la
concentración de la especie corrosiva o del oxígeno entre el ambiente interior y el
exterior de la fisura generan la fuerza motora para la celda de corrosión,
30
especialmente en las áreas que actúan como trampas de agua. Las cavidades son
comunes en situaciones donde hay contacto de metal-a-metal, como en las arandelas
de soporte o en las bridas de tuberías (ductos, caños).
Adicionalmente, los depósitos de desechos y productos de corrosión también generan
cavidades (conocidas como corrosión bajo depósito).
Figura 12 Corrosión en cavidades
Fuente: Propia
2.2.3. Importancia de la corrosión
De las dos clasificaciones de corrosión, la corrosión localizada representa el más
significativo en términos de la necesidad del mantenimiento imprevisto. La corrosión
localizada se oculta a menudo (como en grietas o debajo de capas múltiples de un
recubrimiento de mantenimiento) de tal manera que oculta el verdadero grado del
daño. Debido al riesgo de una perforación rápida del sustrato, ésta puede causar serias
consecuencias si no es detectada y tratada oportunamente. La corrosión localizada
típicamente produce características severas que sirven como “canalizaciones de
esfuerzos”. Estos canalizadores de esfuerzos ocurren bajo condiciones que aumentan
31
el nivel de tensión en el borde principal de una picadura o cavidad, actuando como
los puntos iniciales de la falla.
2.3. Efectos de la corrosión
Los efectos de corrosión incluyen la seguridad, el costo y la apariencia.
2.3.1. Efectos en la seguridad
Las estructuras corroídas pueden ser inseguras en una variedad de maneras. Los
puentes y edificios que deben soportar el peso de cargas extremas son ejemplos
obvios.
La corrosión no puede permitirse en la industria de alimentos y bebidas, donde los
productos de la corrosión del metal contaminarían los alimentos. A menudo se usan
recubrimientos interiores y exteriores para proteger los tanques de proceso y los
envases metálicos de comida.
Figura 13 Plataforma oxidado en puente interconector de tanques
Fuente: Propia
32
2.3.2. Efectos en el costo
La Administración Federal de Carreteras de EE.UU. (FHWA) publicó, a través del
estudio de 2 años en 2002, acerca de los costos directos asociados con la corrosión
metálica en casi todos los sectores de la industria en los EE.UU., desde la
infraestructura y el transporte a la producción y fabricación. Iniciado por NACE
International y el mandato del Congreso de los EE.UU. en 1999 como parte de la Ley
de Equidad en el Transporte para el siglo 21 (TEA -21) , el estudio proporciona
estimaciones de los costos actuales para el tiempo e identifica las estrategias
nacionales para reducir al mínimo el impacto de la corrosión.
El estudio, titulado "Costos de la corrosión y estrategias preventivas en los Estados
Unidos", se llevó a cabo desde 1999 hasta 2001 por CC Tecnologías Laboratories,
Inc., con el apoyo de la FHWA y NACE.
Sus principales actividades incluyen la determinación del costo de los métodos y
servicios de control de la corrosión, para determinar el impacto económico de la
corrosión para sectores industriales específica, la extrapolación de los costos del
sector individuales a un costo total de corrosión nacional, la evaluación de las
barreras a la aplicación efectiva de las prácticas de control de la corrosión
optimizados, y el desarrollo de estrategias de aplicación y ahorro de costes.
Los resultados del estudio muestran que el costo estimado anual total directo de la
corrosión en los EE.UU. es la asombrosa cifra de $ 276000 millones,
aproximadamente el 3,1% del producto interno bruto de la nación lo cual revela que,
si bien la gestión de la corrosión ha mejorado en las últimas décadas, los EE.UU.
deben encontrar más y mejores formas de fomentar, apoyar y aplicar las prácticas
óptimas de control de la corrosión.
33
2.3.3. Efectos en la apariencia
Los recubrimientos desprendidos y el acero oxidado son desagradables para la vista
en cualquier ambiente. Para muchos ingenieros o propietarios de compañías, la
apariencia es una razón primordial para pintar sus estructuras. Por todas las razones
indicadas anteriormente, la prevención de la corrosión es extremadamente importante.
Figura 14 Efectos de la corrosión - apariencia
Fuente: Propia
2.4. Control de la corrosión
Se tiene una variedad de herramientas para controlar la corrosión, las cuales incluyen
el control mediante el método diseño, uso de inhibidores, protección catódica,
recubrimientos protectores, sistemas para zonas de salpique y alteración del ambiente.
2.4.1. Control de la corrosión mediante el método de diseño
El método mediante el cual una estructura está diseñada puede influir en su
resistencia a la corrosión. Generalmente hablando, el diseño para el control de la
corrosión:
34
Elimina la posible acumulación de agua, sales químicas y otro material que podrían
promover la corrosión en puntos específicos (los puntos específicos son áreas
particularmente conducentes a la corrosión acelerada, a menudo designados como
“áreas críticas”).
Los elementos de tal diseño comúnmente incluyen la eliminación de formas
complejas (ej., ángulos de espalda contra espalda) y orientaciones de miembros
estructurales que puedan actuar como “trampas”, proporciona el acceso para las
actividades del mantenimiento que permitirá a los operadores implementar sistemas
de control de la corrosión y, elimina los bordes filosos, cavidades y otros elementos
difíciles de proteger.
2.4.2. Control de la corrosión mediante el uso de inhibidores
Un inhibidor de corrosión es una sustancia que, cuando se agrega a un ambiente,
disminuye la velocidad de corrosión. Los inhibidores de corrosión se agregan
típicamente en cantidades pequeñas al electrolito, típicamente en sistemas cerrados
tales como tuberías (ductos, caños).
2.4.3. Control de la corrosión mediante la selección de materiales
Existen alternativas de materiales de construcción que se pueden corroer menos
rápido que el acero. Escoger un material resistente a la corrosión (CRM) podría ser
requerido en ciertas aplicaciones de la estructura a proteger. Como se fue mencionado
con anterioridad en este capítulo, una serie galvánica es una lista de materiales
ubicados en el orden de sus potenciales de corrosión, iniciando con el que se corroe
más fácilmente o el más activo, al principio y terminando con el que se corroe con
menor facilidad, o el menos activo.
35
2.4.4. Control de la corrosión mediante sistemas de protección catódica
La protección catódica utiliza ánodos de sacrificio hechos de metales más activos
tales como aluminio, zinc o magnesio. Cuando están conectados a la estructura de
acero sumergida que está siendo protegida, entonces estos ánodos se corroen
preferencialmente en lugar de la estructura de acero. Cuando el ánodo de sacrificio
está completamente corroído, debe reemplazarse. El control de la corrosión mediante
la protección catódica en la industria costa afuera casi siempre se usa sin
recubrimientos protectores. Una forma alterna de protección catódica (mediante
corriente impresa) proporciona una corriente eléctrica que contrarresta la corriente de
la celda de corrosión.
2.4.5. Control de la corrosión mediante sistemas de recubrimientos protectores
Los recubrimientos protectores representan el sistema de protección contra la
corrosión para estructuras costa afuera más común y extensivamente usado. El
mecanismo para la protección varía dependiendo del material usado en particular y el
mecanismo elegido puede aislar el sustrato a proteger contra el medio ambiente.
El control de la corrosión mediante el uso de recubrimientos puede ocurrir por uno de
los tres procesos: Recubrimientos de barrera, pigmentos inhibidores y/o sacrificio
(protección catódica).
El recubrimiento de barrera impide la entrada de oxígeno, el agua y las sales solubles.
Los recubrimientos inhibidores, además de servir como una barrera, disminuyen de
forma activa la reacción que ocurre en el ánodo, el cátodo o ambos. Los
recubrimientos de sacrificio usan un metal que es anódico al acero y que se corroe
preferencialmente, esencialmente proporcionan protección catódica.
36
La protección generada por los recubrimientos protectores puede ser influenciada
significativamente por:
Discontinuidades en la película del recubrimiento protector
El tipo de sistema de recubrimiento protector
El espesor del sistema de recubrimientos protectores
La naturaleza del electrolito
Presencia de calamina u otras incrustaciones
2.4.6. Control de la corrosión mediante alteraciones del ambiente
El ambiente, muy a menudo de la superestructura de plataformas marinas, puede ser
modificado para que sea menos corrosivo. Esto tiene que ver principalmente con la
deshumidificación (unidad de deshumidificación en operación). Mientras que ésta es
una práctica común para usos interiores o para una contención instalada
temporalmente, no juega un papel importante en trabajos de control de corrosión en
curso.
Figura 15 Equipo de DH fuera de un tanque
Fuente: Programa de inspectores de recubrimientos nivel 2 Manual del estudiante
37
2.5. Programas de control de la corrosión
Mayormente se mitiga la corrosión estableciendo y manteniendo programas de
control de la corrosión. Los programas individuales variarán en algunos detalles, pero
por lo general se referirán a lo siguiente:
Calificación y especificación de materiales usados en sistemas de protección
contra la corrosión
Especificación del grado de preparación de la superficie
Selección de un sistema de protección contra la corrosión adecuado para un
elemento particular de la estructura
Calificación y selección de contratistas para la aplicación
Establecimiento del control y aseguramiento de la calidad
Calificación y selección de las compañías de inspección en-proceso
Calificación y selección de las compañías de inspección en-servicio
Programación de evaluaciones
Manejo de la data derivada de las evaluaciones
Planificación e ingeniería de las acciones de mantenimiento
Ejecución de las acciones de mantenimiento
Evaluación de la efectividad general del programa de control de la corrosión
2.6. Preparación de la superficie
Para casi todos los procesos de recubrimiento, el primer paso; la limpieza y
preparación inicial de la superficie, es el paso clave para el éxito del sistema de
protección.
Los recubrimientos modernos requieren tanto una superficie limpia así como rugosa
para que puedan tener una estabilidad a largo plazo. La única excepción es si están
38
diseñados específicamente para la aplicación sobre superficies con poca preparación.
Se ha estimado que hasta un 75% de todas las fallas de recubrimiento prematuras son
causadas, ya sea total o parcialmente, por una insuficiente o inadecuada preparación
de la superficie.
2.6.1. Superficies de acero
a) Acero nuevo
El acero nuevo o sin pintar es relativamente fácil de limpiar. Siempre y cuando la
superficie no se haya expuesto a la corrosión en un ambiente químico o marino, es
probable que el problema más grande sea eliminar los depósitos de calamina.
Figura 16 Acero nuevo
Fuente: Propia
b) Acero con recubrimiento existente
Los recubrimientos existentes o antiguos con mala adherencia, o que están demasiado
deteriorados para ser repintados, o los recubrimientos existentes que son
39
incompatibles y se ven afectados por la aplicación de recubrimientos de
mantenimiento, deben ser completamente eliminados mediante lijado, limpieza
abrasiva o remoción química, al igual que cualquier recubrimiento que se está
desprendiendo o degradando de cualquier forma.
Figura 17 Acero con recubrimiento existente
Fuente: Propia
2.6.2. Limpieza previa
El grado de limpieza requerido está estrechamente relacionado con el tipo de
recubrimientos elegidos para su uso, aunque, en general, un mejor nivel de limpieza
proporciona una mejor protección a largo plazo para cualquier sistema de
recubrimientos.
Se debe inspeccionar las superficies en busca de contaminación antes de que inicie la
preparación de la superficie. En caso se encontrase contaminación, la limpieza con
solventes es un método para eliminar todo el aceite, grasa y sucio visibles, así como
compuestos de marcaje y de corte, y otros contaminantes solubles de las superficies
de acero. La intención de la limpieza con solventes es que se utilice antes de la
40
aplicación del recubrimiento y conjuntamente con métodos de preparación de la
superficie especificados para la remoción de óxido, calamina o recubrimiento viejo.
El estándar SSPC-SP 1 es la única norma que normalmente se usa para regir la
limpieza con solventes para eliminar el aceite, grasa, polvo, sucio y compuestos de
marcaje, así como otros compuestos orgánicos similares.
Figura 18 Limpieza previa
Fuente: Propia
Para la remoción de los contaminantes, la SSPC-SP 1 define una variedad de métodos
de limpieza previa, incluyendo la limpieza con solvente usando una tela o trapo, la
inmersión del sustrato en solvente, la atomización de solvente, el desengrasado con vapor, la
limpieza con vapor, la limpieza con agentes emulsionantes, la remoción química del
recubrimiento y el uso de limpiadores alcalinos.
2.6.3. Sales solubles
En ambientes marinos e industriales, donde el aire contiene partículas de sales
químicas, existe la posibilidad que éstas puedan depositarse en la pieza de trabajo. Si
41
esto ocurre después de la limpieza abrasiva y antes de la aplicación, puede ser
necesario lavar y volver a preparar la superficie. La presencia de ciertos depósitos de
sales químicas, como el sulfato ferroso o el hidróxido ferroso, puede determinarse por
medio de papeles de indicadores o equipos de pruebas químicas.
El acero que se ha expuesto a la corrosión en presencia de ciertos contaminantes (ej.,
sulfatos, cloruros) puede ser difícil de limpiar adecuadamente. Aunque la superficie
parezca estar debidamente preparada y libre de productos de la corrosión, puede
contener suficientes contaminantes no visibles creando una superficie inadecuada
para recubrirse. En casos extremos, las áreas muy contaminadas absorberán, después
del arenado, humedad del aire, cambiarán a un color oscuro y rápidamente se
deteriorarán. Este efecto a veces puede verse en minutos después de la culminación
del proceso de limpieza abrasiva, particularmente cuando la humedad es
relativamente alta (una indicación clara de que la superficie está contaminada).
Los siguientes estándares son algunos de los utilizados para varios métodos de
ensayo: SSPC-Guía 15, ISO 8502-2, ISO 8502-5, ISO 8502-6 e ISO 8502-9. En cuanto a la
remoción de las sales solubles, la superficie debe limpiarse exhaustivamente. La
limpieza abrasiva adicional puede ser eficaz en algunos casos, pero se obtiene un
mejor resultado lavándola con equipo de lavado a alta presión. El chorro de agua
también puede ser eficaz para eliminar la contaminación gruesa. La preparación de la
superficie en estos casos debe ser seguida por un análisis de sales ferrosas solubles
y/o cloruros, para asegurar que la contaminación restante esté por debajo de los
niveles críticos.
2.6.4. Limpieza con herramientas manuales
La limpieza con herramientas manuales es un método para preparar las superficies de
acero mediante instrumentos no motorizados. La limpieza con herramientas manuales
42
elimina toda la calamina, óxido, pintura y otro material foráneo perjudicial. La
calamina, el óxido y la pintura adheridos generalmente no pueden eliminarse
mediante este proceso en un ambiente de alta producción. La calamina, el óxido y la
pintura se consideran adheridos si no pueden removerse con una espátula sin filo. Las
herramientas usadas en la limpieza manual incluyen cepillos de alambre, raspadores,
espátulas, cinceles, cuchillos, martillos y piquetas.
Figura 19 Limpieza con herramientas manuales
Fuente: Propia
El estándar escrito usado comúnmente para controlar el proceso de limpieza con
herramientas manuales es SSPC-SP 2, Limpieza con Herramientas Manuales.
2.6.5. Limpieza con herramientas de poder
La limpieza con herramientas de poder es un método para preparar las superficies de
acero usando herramientas mecánicas de limpieza, impulsadas por una fuente de
poder. Estas herramientas son básicamente similares a las herramientas usadas para la
limpieza manual, pero se emplea una fuente de poder como electricidad o aire
comprimido.
43
Este proceso puede eliminar la calamina suelta, óxido, pintura y otro material foráneo
perjudicial, pero no está diseñado para remover calamina, óxido y pintura adheridos.
Al igual que en SSPC-SP 2, la calamina, el óxido y la pintura se consideran adheridos
si no pueden remover levantándolos con una espátula sin filo. Las normas usadas más
comúnmente para regir el proceso de limpieza con herramientas de poder son SSPC-
SP 3 ó ISO 8501 -1 St 3 (o St 2).
Figura 20 Limpieza con herramientas de poder
Fuente: Propia
Los estándares escritos para la limpieza con herramientas de poder son:
SSPC-SP 3 pide una limpieza con herramientas de poder para remover toda la
calamina, herrumbre, pintura y demás material foráneo perjudicial que estén sueltos.
No es la intención remover calamina, óxido, y pintura firmemente adheridos
mediante este proceso. La calamina, el óxido y la pintura se consideran adheridos
cuando no se pueden levantar con una espátula sin filo.
El estándar SSPC-SP 11 pide una limpieza con herramientas de poder para producir
una superficie de metal desnudo y retener o crear un perfil, cuando se requiere en un
sustrato a metal desnudo, limpio y rugoso, pero donde la limpieza abrasiva no es
44
posible o permitida. Las superficies metálicas preparadas según SSPC-SP 11, el verse
sin magnificación, deben estar libres de todo aceite, grasa, sucio, polvo, calamina,
óxido, pintura, productos de corrosión y otros materiales foráneos visibles. Ligeros
residuos de óxido y pintura pueden estar presentes en el fondo de las picaduras si
estas existen en la superficie original. Si se especifica el pintado, la superficie debe
quedar rugosa, a un grado adecuado para el sistema de pintura, con un perfil no
menor de 25 μm (1 mil).
Los estándares visuales para la limpieza con herramientas de poder son la SSPC-VIS
3 y la ISO 8501-1 (St 3 ó St 2).
2.6.6. Limpieza abrasiva
Una excelente forma para preparar y limpiar la superficie del acero o de otros
materiales es el chorro abrasivo, que consiste en impactar partículas abrasivas a gran
velocidad sobre el área que se quiere limpiar. Esta acción permite remover el óxido
de laminación, los productos de corrosión y en general toda impureza o
suciedad presente en la superficie.
La impulsión de las partículas se realiza por medios neumáticos utilizando aire a
presión, o por accionamiento eléctrico de una rueda centrífuga que impulsa las
partículas. De esta forma, se logra limpiar efectivamente la superficie y prepararla
para lograr una buena adherencia de los recubrimientos que serán aplicados sobre
ella.
La limpieza con chorro abrasivo, es el mejor método para acondicionar la
superficie que posteriormente debe ser pintada para obtener una perfecta adherencia
del recubrimiento. Esto se logra porqué adicionalmente al grado de limpieza
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determinado se aumenta la superficie de contacto entre pintura y sustrato creando una
rugosidad en la base.
Figura 21 Limpieza abrasiva seca
Fuente: Propia
Existen muchos productos que se utilizan como abrasivos y entre ellos destacamos:
arena de río, granalla de acero redonda y angular, escoria de cobre, cuarzo, hielo seco
(CO2), cascara de nueces, óxido de zinc, granalla de plásticos, entre otros. En algunos
casos es posible utilizar arena mezclada con agua para así reducir la contaminación de
polvo en el ambiente, en este caso se moja la superficie y deberán usarse las pinturas
o revestimientos compatibles con esta situación.
a) Estándares escritos de limpieza de la superficie
Se han definido varios grados o estándares de limpieza superficial alcanzados
mediante chorro abrasivo. Los estándares de limpieza abrasiva para el acero nuevo
que son utilizados con mayor frecuencia en aplicaciones de preparación de la
superficie por este medio son producidos por NACE, SSPC e ISO. En Octubre de
46
1994, NACE y SSPC publicaron los siguientes estándares conjuntos para la
preparación de la superficie mediante limpieza abrasiva:
NACE Nº 1 / SSPC-SP 5, Limpieza Abrasiva a Metal Blanco
Una superficie preparada mediante limpieza abrasiva a metal blanco, al
inspeccionarse sin magnificación, estará libre de todo visible: Aceite, Grasa, Polvo,
Sucio, Calamina, Herrumbre, Recubrimientos, Óxidos, Productos de corrosión y Otro
material foráneo.
NACE Nº 2 / SSPC-SP 10, Limpieza Abrasiva a Metal Casi Blanco
Una superficie preparada mediante limpieza abrasiva a metal casi blanco, al
inspeccionarse sin magnificación, estará libre de todo visible: Aceite, Grasa, Polvo,
Sucio, Calamina, Herrumbre, Recubrimientos, Óxidos, Productos de corrosión y Otro
material foráneo excepto por manchas.
Las manchas se limitarán a no más del 5% de cada unidad de área de superficie de
aproximadamente 6.400 mm2 (9 in.2) (es decir, un cuadrado de 80 x 80 mm. [3 x 3
in.]), y pueden consistir de ligeras sombras y rayas ligeras o decoloraciones menores
causadas por la herrumbre, calamina y/o recubrimientos anteriores.
NACE Nº 3 / SSPC-SP 6, Limpieza Abrasiva Comercial
Una superficie preparada mediante limpieza abrasiva al grado comercial, al
inspeccionarse sin magnificación, estará libre de todo visible: Aceite, Grasa, Polvo,
Sucio, Calamina, Herrumbre, Recubrimientos, Óxidos, Productos de corrosión y Otro
material foráneo excepto por manchas.
Las manchas aleatorias se limitarán a no más del 33% de cada unidad de área de
superficie de aproximadamente 6.400 mm.2 (9 in.2) (es decir, un cuadrado de 80 x 80
mm. [3 x 3 in.]) y pueden consistir de ligeras sombras, rayas ligeras o decoloraciones
47
menores causadas por manchas de herrumbre, manchas de calamina y/o manchas del
recubrimiento anterior.
NACE Nº 4 / SSPC-SP 7, Limpieza Abrasiva Superficial o “Brush-Off”
Una superficie preparada mediante limpieza abrasiva superficial, al ser inspeccionada
sin magnificación, estará libre de todo visible: Aceite, Grasa, Polvo, Sucio, Calamina
suelta, Óxido suelto y Recubrimientos sueltos.
La calamina, el óxido y los recubrimientos que estén firmemente adheridos, pueden
permanecer en la superficie. La calamina, el óxido y los recubrimientos se consideran
firmemente adheridos si no pueden levantarse con una espátula sin filo. Toda la
superficie se someterá a limpieza abrasiva. La calamina, el óxido y los recubrimientos
remanentes deberán quedar firmemente adheridos.
NACE Nº 8 / SSPC-SP 14, Limpieza Abrasiva Industrial
Una superficie preparada mediante limpieza abrasiva industrial, al ser inspeccionada
sin magnificación, estará libre de todo visible: Aceite, Grasa, Polvo y Sucio. Restos
de calamina, óxido y residuos de recubrimiento, firmemente adheridos, se permiten
que permanezcan en un 10% de cada unidad de área superficial, si están distribuidos
homogéneamente. Los restos de calamina, óxido y recubrimientos se consideran
firmemente adheridas si no pueden desprenderse con una espátula sin filo. Sombras,
marcas y decoloraciones, causadas por manchas de óxido, manchas de calamina y
manchas de recubrimientos anteriores pueden estar presentes en el resto de la
superficie.
b) Estándares visuales
SSPC-Vis 1 Estándar Visual para la Limpieza Abrasiva del Acero. Este estándar
visual consiste en fotografías de referencia para superficies de acero preparadas por
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limpieza abrasiva, usando arena como abrasivo. Se diseñaron para complementar las
especificaciones escritas de SSPC sobre preparación de la superficie mediante
limpieza abrasiva, y no para substituir estas especificaciones.
2.6.7. Chorro de agua (Waterjetting)
El chorro de agua (waterjetting) es el uso de una corriente de agua de alta presión
para desprender recubrimientos existentes y para limpiar superficies.
Este método tiene ciertas ventajas sobre la limpieza con abrasivo en seco,
especialmente en lo que respecta a la seguridad y a la calidad del aire del trabajador.
Con el chorro de agua, los requisitos respiratorios pueden ser menos exigentes que
aquéllos para otros métodos de preparación de la superficie.
El chorro de agua usa sólo agua, sin la adición de partículas sólidas como arena o
granate en la corriente de agua, con presiones de operación hasta de 414 MPa (60,000
psig). Sin embargo, con el continuo desarrollo de la tecnología y equipos, ya es
posible usar mayores presiones de operación.
Este método de limpieza es particularmente adecuado para la industria de procesos,
plantas de electricidad, y otras plantas dónde los recubrimientos de alto rendimiento
requieren grandes superficies de preparación y/o descontaminación superficial, y se
usa ampliamente en la industria marina para remover el crecimiento marino y
preparación de interiores de tanques de almacenamiento.
El chorro de agua no produce un perfil o grabado como lo hace la limpieza con
abrasivo; más bien, expone el perfil de superficie original. Por lo tanto, el chorro de
agua generalmente se usa en proyectos de recubrimiento y revestimiento donde los
sustratos tienen un perfil pre-existente adecuado.
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Figura 22 Chorro de agua
Fuente: Revista JPCL Ultra High Pressure Waterjetting
Para ser un medio de limpieza efectivo, el agua utilizada para el chorro de agua debe
ser pura, para que no contamine al limpiar la superficie. Para evitar el daño al equipo,
el agua debe estar libre de partículas sólidas y de sedimentos.
Para apreciar bien al chorro de agua como un método de preparación de la superficie
y para aquéllos usando la nueva Norma de NACE/SSPC, es necesario introducir
algunas definiciones y descripciones para la limpieza de la superficie:
Limpieza con Agua a Baja Presión (LP WC): Limpieza realizada a presiones
menores de 34MPa (5.000 psig). Esto se conoce también como “lavado a
presión”.
Limpieza con Agua a Alta Presión (HP WC): Limpieza realizada a presiones
de 34 a 69 MPa(5.000 a 10.000 psig)
Chorro de Agua a Alta Presión (HP WJ): Limpieza realizada a presiones de 70
a 207 MPa(10.000 a 30.000 psig)
Chorro de Agua a Ultra Alta Presión (UHP WJ): Limpieza realizada a
presiones por encima de 207 MPa (30.000 psig)
50
Limpieza con Agua a Baja Presión (LP WC)
La limpieza con agua a baja presión (LP WC), usada para la preparación de la
superficie, es principalmente una técnica de lavado. A presiones menores de 34 MPa
(5.000 psi), el agua elimina los contaminantes solubles y algunos contaminantes
superficiales sueltos. Removerá bien el caleamiento (tizamiento) de pinturas
envejecidas, dejando la superficie del recubrimiento intacta.
La limpieza con agua a baja presión se usa a menudo para lavar las partes inferiores
de barcos en dique seco, removiendo el crecimiento marino y algunos recubrimientos
anti-incrustantes (antifoulings) deteriorados, antes de volver a pintar.
Limpieza con Agua a Alta Presión (HP WC)
La limpieza con agua a alta presión (HP WC) normalmente se usa para la preparación
de superficies de concreto (hormigón) antes de la aplicación del recubrimiento.
Utilizando boquillas debidamente enfocadas, el equipo de HP WC puede cortar a
través de una placa de acero o bloques de concreto, así que la técnica puede ser tanto
eficiente como peligrosa. Cuando se usa en la preparación de la superficie para los
recubrimientos, la tasa de producción es relativamente baja. Adicionalmente,
solamente puede eliminarse correctamente la contaminación suelta.
Chorro de Agua a Alta Presión (HP WJ)
El equipo de chorro de agua a alta presión (HP WJ) raramente se usa para la
preparación de superficies a recubrir. El efecto de limpieza no es mejor que el equipo
que opera a presiones más bajas, y la tasa de producción no es efectivo en relación al
costo.
Chorro de Agua a Ultra Alta Presión (UHP WJ)
Este método usa agua a presiones muy altas – 207 MPa (30.000 psi) y más (hasta 345
MPa [50.000 psi]). Debido a las altas presiones requeridas, la práctica segura exige
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sumo cuidado para controlar las boquillas del chorro de agua, ya que una persona que
sea golpeada por agua a alta velocidad y a corta distancia podría resultar seriamente
lesionada.
La mayoría de los equipos para UHP WJ operan con una boquilla giratoria y chorros
de agua duales. El diseño de la boquilla de alta eficiencia produce un patrón de
limpieza efectivo, usando relativamente poca agua, quizás no más de 8 L (2 gal.) por
minuto. Se debe mantener la boquilla cerca de la superficie que se está preparando, ya
que el efecto de limpieza disminuye rápidamente a medida que ésta se aleja del
sustrato. El chorro de agua casi no tiene efecto alguno sobre la superficie si la
distancia boquilla-sustrato es superior a los 50 cm. (18 in.). El efecto de limpieza más
efectivo se obtiene a una distancia de aproximadamente 50 mm. (2 in.), aunque el
patrón de chorreado será muy pequeño y las tasas de producción pueden disminuir.
El agua usada a esta presión elimina la mayoría de los contaminantes, como sales
químicas, sucio, grasa e incrustaciones de óxido. No producirá un perfil de anclaje,
pero puede restaurar el perfil superficial anterior, siempre y cuando el equipo esté
diseñado para limpiar el sustrato a un estándar alto. Esto por lo general se logra
solamente operando a las presiones más altas (240 MPa [35.000 psi.] y superiores).
Un beneficio incidental de las presiones muy altas es un efecto de calentamiento
sobre la superficie que se está preparando. En el caso del acero, este calor tiene el
efecto de limitar el deterioro por la oxidación, quedando la superficie relativamente
limpia (aunque con algo de decoloración jengibre).
a) Estándares de la preparación superficial
El 25 de Junio del 2012, NACE International retira la norma NACE 5/ SSPC-SP 12
“Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating” y
es reemplazado con 4 nuevas normas comunes:
52
SSPC-SP WJ-1 / NACE WJ-1: Limpieza a metal desnudo
Una superficie de metal después de la limpieza de sustrato desnudo, vista sin
aumento, tendrá un acabado mate (opaco, con manchas) y deberá estar libre de
contaminantes visibles aceite, grasa, suciedad, óxido y otros productos de corrosión,
recubrimiento viejo, escamas de laminación y materia extraña.
Alcances:
Las películas delgadas de cascarilla de laminación, óxido y otros productos de
corrosión, y recubrimiento no están permitidos.
La coloración gris a marrón negruzco que queda en el acero al carbono corroído
y con pits que no puede ser eliminado mediante una mayor limpieza por chorro
de agua está permitido.
NACE VIS 7/SSPC-VIS 4 u otra guía visual o de comparación puede ser
especificado como complemento a la definición escrita. En caso de litigio, la
norma escrita, prevalecerá sobre la guía visual.
SSPC-SP WJ-2 / NACE WJ-2: Limpieza muy exhaustiva
Una superficie de metal después de la limpieza muy exhaustiva, cuando se ve sin
aumento, tendrá un acabado mate (opaco, con manchas) y deberá estar libre de todo
contaminante visible, aceite, grasa, suciedad, óxido y otros productos de corrosión,
excepto para manchas dispersas al azar de óxido y otros productos de corrosión,
recubrimientos delgados muy adheridos y otras materias extrañas firmemente
adheridas. Las manchas o materia firmemente adherida se limita a no más de 5 % de
cada unidad de área de superficie y puede consistir en manchas dispersas al azar de,
óxido y otros productos de corrosión o de recubrimiento aplicado anteriormente,
recubrimientos delgados fuertemente adheridos, y otras materias extrañas firmemente
adheridas.
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Alcances:
Una unidad de área de superficie, es un área de aproximadamente 5.800 mm2
[9,0 pulg2] (es decir, un cuadrado de 76 mm x 76 mm [3.0 pulg x 3,0 pulg].
Pinturas, cascarilla de laminación, y otras materias extrañas se consideran
fuertemente adheridas si no se puede quitar levantando con una espátula sin filo.
La coloración gris a marrón-negruzco que queda en el acero al carbono corroído
y con pits, que no puede ser eliminado mediante una mayor limpieza por chorro
de agua no se considera parte del porcentaje de mancha.
SSPC-VIS 4/NACE VIS 7 u otra guía visual o de comparación puede ser
especificado como complemento a la de la definición escrita. En caso de litigio,
el estándar escrito tendrá prioridad sobre la guía visual o de comparación.
SSPC-SP WJ-3 / NACE WJ-3: Limpieza profunda
Una superficie de metal después de la limpieza a fondo, cuando se ve sin aumento,
tendrán un acabado mate (opaco, con manchas) y deberá estar libre de todo
contaminante visible aceite, grasa, suciedad, óxido y otros productos de corrosión,
excepto para las manchas dispersas al azar de óxido y otros productos de corrosión,
pinturas delgadas bien adheridas y otras materias extrañas firmemente adheridas. Las
manchas o materia fuertemente adherida se limita a no más de 33 % de cada unidad
de área de superficie y puede consistir en manchas dispersas al azar de óxido y otros
productos de corrosión o de pintura antigua, pinturas delgadas fuertemente adheridas,
y otras materias extrañas firmemente adheridas.
Alcances:
Una unidad de área de superficie, es un área de aproximadamente 5.800 mm2
[9,0 pulg2] (es decir, un cuadrado de 76 mm x 76 mm [3.0 pulg x 3,0 pulg].
Recubrimietos, cascarilla de laminación, y otras materias extrañas se consideran
fuertemente adheridas si no se puede quitar levantando con una espátula sin filo.
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La coloración gris a marrón-negruzco que queda en el acero al carbono y
corroído con pits que no puede ser eliminado mediante una mayor limpieza por
chorro de agua está permitido.
SSPC-VIS 4/NACE VIS 7 u otra guía visual o de comparación puede ser
especificado como complemento a la definición escrita. En caso de litigio, el
estándar escrito tendrá prioridad sobre la guía visual o de comparación.
SSPC–SP WJ-4 / NACE WJ-4: Limpieza ligera o superficial
Una superficie de metal después de la limpieza ligera, cuando se ve sin aumento,
debe estar libre de todo contaminante visible, aceite, grasa, suciedad, polvo, escamas
de laminación sueltas, óxido suelto, otros productos de corrosión, y recubrimiento
suelto. Cualquier residuo adherido firmemente al substrato de metal y puede consistir
en manchas dispersas al azar de óxido y otros productos de corrosión o de pintura
antigua, pinturas delgadas fuertemente adheridas, y otras materias extrañas
firmemente adheridas pueden quedar sobre la superficie.
Alcances:
Recubrimientos y escamas de laminación y otras materias extrañas se consideran
fuertemente adherido si no se puede quitar levantando con una espátula sin filo.
La coloración gris a marrón-negruzco que queda en el acero al carbono corroído
y con pits que no puede ser eliminado mediante una mayor limpieza por chorro
de agua está permitido.
SSPC-VIS 4/NACE VIS 7 u otra guía visual o de comparación puede ser
especificado como complemento a la definición escrita. En caso de litigio, el
estándar escrito tendrá prioridad sobre la guía visual o de comparación.
SSPC-Vis 4 / NACE VIS 7: Guía y Referencia Fotográfica para Superficies de
Acero preparados por Waterjetting
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Este estándar visual consiste en fotografías de referencia para superficies de acero
preparadas por Chorro de Agua (Waterjetting).
b) Consideraciones adicionales
Óxido prematuro (Flash Rust)
El óxido prematuro (Flash Rust) es una consideración adicional a tomarse en cuenta,
cuando un sustrato de acero al carbono se somete a limpieza por chorro de agua. La
coloración gris o marrón-negruzco que queda en los pits de acero al carbono cuando
se limpia por chorro de agua no es la oxidación superficial. En los metales que no son
de acero al carbono puede manifestarse como una decoloración también.
Grados de oxidación superficial puede ser cualitativamente descrito como sigue:
No oxidada (No Flash Rust): Una superficie de acero que, cuando se observa
sin amplificación, no exhibe ningún óxido visible.
Figura 23 No oxidada
Fuente: Propia
Flash Rust Ligero (L): Una superficie que, cuando se observa sin amplificación,
exhibe cantidades pequeñas de una capa de óxido amarillo café, a través del cual
56
se puede observar el sustrato de acero. El óxido o decoloración puede estar
distribuida uniformemente o presente por zonas, pero está fuertemente adherida y
no se quita fácilmente con un paño pasado ligeramente sobre la superficie.
Figura 24 Flash rust ligero (L)
Fuente: Propia
Flash Rust Moderado (M): Una superficie de acero al carbono que, cuando se
observa sin amplificación, exhibe una capa de óxido amarillo-café que oscurece
la superficie original del acero. La capa de óxido puede estar incluso distribuida
uniformemente o presente por zonas, pero está razonablemente bien adherida y
deja marcas ligeras en un paño pasado ligeramente sobre la superficie (ver figura
25).
Flash Rust Pesado (H): Una superficie de acero al carbono que, cuando se
observa sin amplificación, exhibe una capa densa de óxido rojo-castaño que
esconde completamente la condición inicial de la superficie. El óxido puede estar
incluso distribuido uniformemente o presente en zonas, pero el óxido que está
ligeramente adherido, fácilmente se desprende dejando marcas significantes en
un trapo que se frota ligeramente sobre la superficie (ver figura 26).
57
Figura 25 Flash rust moderado (M)
Fuente: Propia
Figura 26 Flash rust pesado (H)
Fuente: Propia
Inhibidores
En el chorro de agua y otras operaciones de limpieza similares que usan agua, a veces
se agrega un inhibidor al líquido para ayudar a evitar la oxidación de la superficie
preparada antes de aplicar el recubrimiento. Esto sólo aplica, por supuesto, al preparar
superficies de acero (ferrosas). Los problemas potenciales asociados con la adición de
inhibidores incluyen:
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La cantidad de inhibidores debe controlarse cuidadosamente. El depósito de
cantidades excesivas de inhibidor en una superficie probablemente evitará
adecuadamente la formación de óxido, pero también es probable que interfiera
con la adhesión del recubrimiento. De igual forma, la deposición de muy poco
inhibidor sobre la superficie afectará la propiedad de brindar la protección contra
la formación del óxido.
Es probable que los depósitos de inhibidor interfieran con el desempeño a largo
plazo del recubrimiento.
La introducción de una capa química entre el sistema de recubrimientos y la
superficie preparada es polémica y ha sido criticada por expertos que dicen que
debilita la protección suministrada por el sistema de recubrimientos.
Generalmente se agregan inhibidores al agua en forma de sólidos solubles,
añadidos al recipiente del líquido, o en un líquido concentrado, agregado a la
corriente de limpieza mediante la dosificación con un inyector. El uso exitoso de
los inhibidores depende de la consistencia del método escogido.
Recubrimientos Tolerantes a la Humedad
Una desventaja del chorro de agua (waterjetting) de cualquier tipo, es que la cantidad
de agua usada humedece el ambiente y la superficie. En general, la superficie debe
dejarse secar antes de aplicar los recubrimientos, o deben usarse recubrimientos
especiales tolerantes a la humedad.
Algunos fabricantes de recubrimientos han desarrollado productos, a menudo basados
en la tecnología epóxica, que pueden aplicarse directamente a una superficie húmeda.
El uso de estos recubrimientos incrementa mucho la conveniencia de usar este
método de preparación de la superficie. Algunos de estos recubrimientos especiales
están diseñados como tolerantes de condiciones húmedas, otros como tolerantes a
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condiciones mojadas. Debe tenerse cuidado para determinar qué tan húmeda estará la
superficie en el momento de la aplicación.
2.7. Sistema de recubrimientos
Para definir un sistema de recubrimientos, se debe tener en cuenta:
Método de preparación de la superficie utilizado
Equipo de aplicación y procesos
Los materiales utilizados para una o más capas de recubrimiento
2.7.1. Sistemas de una capa
Durante muchos años la premisa principal era que un sistema de recubrimiento de
una capa no era suficiente para proteger una estructura industrial. Sin embargo, con
las nuevas tecnologías, los avances en los equipos de aplicación y la capacitación de
los trabajadores del oficio, ahora es posible tener un sistema de capa única para
ciertas aplicaciones.
Productos epóxicos y poliuretanos libres de solvente se están empleando actualmente
en la protección contra la corrosión en muchos sectores de la industria. Como
recubrimiento interior de tanques, tanto en la industria marítima como en el sector de
tratamiento de aguas residuales, se están utilizando estos sistemas de capa única y
algunos fabricantes están promoviendo su uso en otras áreas.
Un sistema de capa única requiere que el aplicador aplique el material con mucho
cuidado, y que el inspector revise cuidadosamente la superficie en busca de
discontinuidades (holidays) u otros defectos. Se requieren equipos especializados y
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una planificación de la aplicación para facilitar el acceso en algunas instalaciones o
en espacios confinados.
2.7.2. Sistemas de recubrimientos multicapa
En la mayoría de los casos, un sistema de recubrimientos multicapa se utiliza en
trabajos industriales y marinos. Existen numerosas razones para utilizar un sistema de
multicapa. La primera es que en muchos casos ciertos materiales funcionan muy bien
en un aspecto de la protección contra la corrosión, pero no tan bien en otras áreas. El
sistema más común es el uso de un IOZ (recubrimiento de zinc inorgánico) como
primario (imprimante, fondo), en primer lugar por su excelente adherencia al acero y
su capacidad para proporcionar una protección catódica en los cortes y reducir el
riesgo de corrosión subcutánea. La segunda capa normalmente es un epoxico de alto
espesor, utilizada como una capa barrera para reducir la penetración de la humedad
en el sustrato. La capa de acabado en un sistema exterior es típicamente un
poliuretano, utilizado por su excelente resistencia a los rayos UV.
2.7.3. Compatibilidad
¡No todas las capas funcionan bien juntas! Un ejemplo clásico es la aplicación de un
recubrimiento alquídico sobre zinc inorgánico o galvanizado, cuyas películas
desarrollan un pH alto, formando un material jabonoso. Los ácidos grasos en los
alquídicos reaccionan (saponificación) entre las dos capas. Hay alquídicos que han
sido modificados con resina fenólica para que esta reacción no ocurra. Otro error
común es aplicar una capa de curado químico sobre un recubrimiento de curado por
evaporación de solventes. Los solventes fuertes en la capa superior ablandan la capa
de abajo y el estrés generado durante el curado del acabado levantará el material
ablandado de la superficie.
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2.8. Defectos de Recubrimientos
2.8.1. Película que no seca (falta de curado)
Con frecuencia causados simplemente por no añadir el agente de curado a la base,
añadir el agente de curado equivocado o no agregar la cantidad correcta de agente de
curado durante la mezcla (ver figura 27).
Otros asuntos que podrían inhibir el proceso de curado del recubrimiento son:
Problema con el recubrimiento enviado por el fabricante del producto, una
revisión con el fabricante, con el número de lote a la mano, puede dar una
respuesta rápida.
Aspectos ambientales: demasiado frío, demasiado calor, demasiado húmedo.
Solvente equivocado o contaminado, la humedad en algunos solventes genéricos
puede reaccionar en el proceso de curado.
2.8.2. Exudación de amina
Si el proceso de curado de los recubrimientos epoxy curados con aminas ocurre en
condiciones de bajas temperaturas ambientales, temperaturas en disminución o de alta
humedad, se puede desarrollar un aceite superficial o exudado, comúnmente conocida
como “exudación de amina”. Esto es causado por la absorción de dióxido de carbono
y agua en la película del recubrimiento y reaccionando con el agente de curado de
amina (ver figura 28).
Algunos de los problemas asociados a esta falla pueden ser:
Superficie con pegajosidad o grasosa
Curado incompleto
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Mala adherencia y mala adherencia al repintar
Decoloración del recubrimiento con el paso de tiempo
Escasa retención del brillo
Figura 27 Recubrimiento sin curar
Fuente: Propia
Figura 28 Exudación de amina
Fuente: Blooming and Blushing por Ing. de Campo José Galindo
2.8.3. Escurrimiento, colgamiento, cortinas, arrugas
Estos defectos pueden ser provocados o empeorados por:
La aplicación de una capa demasiado gruesa
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El exceso de diluyente o el uso de un solvente equivocado
Una superficie demasiado caliente para aplicar el recubrimiento
Aplicación del recubrimiento al final del tiempo de vida útil de la mezcla
Tixotropía equivocada utilizada en la fabricación
Técnica de aplicación inadecuada
Figura 29 Escurrimiento
Fuente: Propia
2.8.4. Discontinuidades, saltos, holidays, áreas desnudas
Estos defectos consisten en áreas expuestas del sustrato o de la capa anterior,
causadas por malas técnicas de aplicación, falta de aplicación de la capa franja y/o la
falta de o una pobre inspección (ver figura 30).
2.8.5. Caleamiento
El caleamiento es una capa polvorienta, de partículas muy finas del material, sobre la
superficie del recubrimiento normalmente causada por la exposición a la luz
ultravioleta, pero también puede deberse a la exposición a otras formas de radiación,
como la radiación nuclear.
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Figura 30 Holidays
Fuente: Propia
Es causado por la ruptura de los enlaces entre las moléculas en la película de pintura.
Es más común en los recubrimientos epóxicos, pero se puede producir en casi todos
los recubrimientos si se les deja expuestos a las condiciones causales por un periodo
suficientemente largo de tiempo.
Figura 31 Caleamiento
Fuente: Propia
2.8.6. Formación de cráteres
Los cráteres son la formación de pequeñas depresiones en forma de tazón en el
recubrimiento aplicado causado por el aire atrapado en la película, formando una
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burbuja que luego estalla, dejando el cráter. El cráter es común en los recubrimientos
aplicados con rodillo o brocha por un aplicador sin experiencia. La formación de
cráteres puede ser causada por el aire atrapado en el recubrimiento durante la mezcla,
si no se respetan los procedimientos adecuados de mezclado.
Figura 32 Cráteres
Fuente: Propia
2.8.7. Puntos de alfiler
Los puntos de alfiler son orificios muy pequeños en la película, por lo general
causados al pintar sobre un zinc inorgánico (IOZ) o sobre recubrimientos de
metalizados. Son ocasionados por el aire o solvente atrapado en la película porosa
que trata de escapar. Los recubrimientos de zinc se secan tan rápidamente que los
pequeños orificios no se vuelven a llenar (ver figura 33).
2.8.8. Ampollamiento
Las ampollas forman una proyección en la película de recubrimiento desde el
sustrato, por lo general en forma circular o de domo. Las ampollas pueden tener una
forma irregular dependiendo de la causa. Pueden estar llenas con agua pura, gas,
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solvente, sustancia cáustica, oxígeno, cristales o herrumbre. La causa fundamental es
la pérdida de adherencia en zonas localizadas (ver figura 34).
Figura 33 Pinholes o puntos de alfiler
Fuente: Propia
Muchos factores pueden conducir a la formación de ampollas, las más comunes
incluyen algún tipo de contaminante que queda en la superficie después de la
limpieza:
En servicio atmosférico, las ampollas pueden ser causadas por pintar sobre
aceite, humedad, grasa, suciedad, polvo, pigmentos solubles, o puede ocasionarse
por solvente atrapado.
En servicio de inmersión o en estructuras enterradas también pueden producirse
por electro-endósmosis, debido a una actividad excesiva del sistema de
protección catódica, corrientes parásitas o por ósmosis causada por sales solubles
atrapadas.
2.8.9. Agrietamiento (cuarteamiento) y desprendimiento
Estos son defectos en forma de grietas visibles en la película que pueden penetrar
hasta el sustrato o simplemente a través de una sola capa en un sistema multicapa. La
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principal causa está relacionada con esfuerzos, ya sea debido al movimiento del
sustrato o la tensión interna en el recubrimiento a medida que envejece.
Figura 34 Ampollamiento
Fuente: Visual comparison manual Application and coating defects, Brendan
Fitzsimons
Los recubrimientos químicamente curados, aplicados demasiado gruesos, son
propensos a agrietarse. Otras causas incluyen la absorción y evaporación de
humedad.
Figura 35 Cuarteamiento
Fuente: Propia
2.8.10. Fallas de adhesión: en cáscara, delaminación y desprendimiento
Estos defectos se deben a la pérdida de adhesión entre las capas del recubrimiento o
entre este y el sustrato, debido a:
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Contaminación en la superficie sobre la cual se aplicó el recubrimiento
Preparación incorrecta de la superficie especificada
Falta de inspección de la preparación de la superficie
Perfil de anclaje insuficiente
Exceder la ventana de repintado del material
Aplicación de recubrimientos incompatibles, como un recubrimiento alquídico
sobre un zinc inorgánico
Aplicación de un recubrimiento a una superficie brillante
Figura 36 Fallas de adhesión
Fuente: Propia
2.8.11. Fallas en soldaduras y bordes
A no ser preparados mediante una capa de franja, una fuente común de fallas de los
recubrimientos en servicio es la corrosión que se inicia en un borde afilado o en un
cordón de soldadura irregular o con salpicaduras. La razón fundamental es que los
recubrimientos se retirarán de un borde afilado y la aplicación industrial mediante
atomización o rodillo hará que el recubrimiento forme un puente sobre pequeñas
depresiones en el sustrato.
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Figura 37 Bordes
Fuente: Propia
2.8.12. Muescas o puntos astillados
Las muescas o puntos astillados son causados por mover equipos alrededor del
proyecto, causando estos daños que normalmente llegan hasta el sustrato. Incluso en
un pequeño punto astillado comenzará una celda de corrosión activa y puede causar la
formación de una picadura.
2.9. Pruebas de inspección
Se utiliza una variedad de pruebas e instrumentos de prueba para asegurar que las
aplicaciones alcancen la vida útil esperada.
2.9.1. Condiciones ambientales
Las condiciones ambientales pueden tener un efecto en el proceso de preparación de
superficie, así como en la superficie preparada antes de pintar. Las condiciones
ambientales incluyen:
Temperatura del aire (y temperatura del sustrato); no es prudente realizar la
preparación superficial si la superficie del acero está más fría que el aire circundante.
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La humedad puede condensarse en la superficie preparada, causando que se oxide
instantáneamente. La temperatura del sustrato puede revisarse usando un termómetro
de superficie.
Figura 38 Termómetro de superficie
Fuente: Propia
Humedad relativa; durante las operaciones de preparación de superficie, la humedad
alta puede producir un rápido deterioro de la superficie preparada. La preparación
superficial final y la aplicación de recubrimientos no debe realizarse en condiciones
húmedas (es decir, cuando llueve o cuando la humedad relativa sea muy alta,
generalmente mayor al 85%).
Punto de rocío; se define como la temperatura a la que ocurre la condensación. Si la
temperatura ambiente cae por debajo del punto del rocío, o si algunas o todas las
estructuras tienen una temperatura por debajo del punto del rocío, entonces ocurrirá la
condensación. Si la preparación superficial se realiza cuando las condiciones
ambientales están cerca de la temperatura del punto de rocío, es probable que ocurra
la condensación y la oxidación instantánea. Por esta razón, las especificaciones de
recubrimientos normalmente requieren que no se apliquen recubrimientos si la
temperatura del acero o del aire circundante es menor que 3° C (5° F) sobre el punto
de rocío.
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El punto de rocío, como la HR, se calcula haciendo mediciones de temperatura con
un higrómetro o psicrómetro giratorio.
Figura 39 Psicrómetro giratorio
Fuente: Propia
2.9.2. Preparación de la superficie
La inspección de la preparación de superficie consiste en un análisis visual, tanto del
grado de limpieza como del perfil de anclaje desarrollado en la superficie por el
método utilizado.
Al hacer la inspección, generalmente son utilizadas guías visuales estandarizadas de
la NACE o de la SSPC, las cuales sirven de testigos comparativos para cada grado de
limpieza de superficie.
La profundidad del perfil de anclaje puede evaluarse mediante varios métodos:
Comparadores y cupones
Cintas réplica
Micrómetro de profundidad (profilómetro)
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Figura 40 Determinación del perfil de anclaje mediante cinta réplica
Fuente: Propia
2.9.3. Sales solubles
Es esencial que el nivel de contaminantes en una superficie se mida antes de la
aplicación del recubrimiento, con el fin de asegurar que se obtenga la calidad y la
vida óptima del recubrimiento.
La contaminación de la superficie por sales como cloruros, sulfatos y nitratos se ha
demostrado que causa el ampollamiento de los recubrimientos orgánicos, en
particular en condiciones de inmersión.
Las sales solubles no son visibles y requieren que se efectúen diversos ensayos para
determinar su presencia, tales como:
Parche Bresle
Prueba de la Manga
Medidores de Sales Solubles
Conductividad
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Figura 41 Extracción de las sales solubles sobre la superficie preparada
mediante parche bresle
Fuente: Propia
2.9.4. Medición de espesores de película seca
Se realizan mediciones de la película seca del recubrimiento de acuerdo a lo
requerido, se utilizan varios tipos de medidores de película seca, siendo el más común
el medidor electrónico (medidor tipo II).
Figura 42 Medición de espesores de película seca (medidor tipo II)
Fuente: Propia
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2.9.5. Adherencia de recubrimientos
La mayoría de los recubrimientos aplicados adecuadamente sobre una superficie bien
preparada tienen buena adherencia al sustrato. Sin embargo, algunos usuarios pueden
elegir realizar algún tipo de pruebas de adherencia para determinar la calidad de la
unión del recubrimiento al sustrato, así como entre los recubrimientos.
Algunas de estas pruebas de adherencia son:
Cuchilla (ASTM D 6677)
Cinta de desprendimiento Pull-Off (ASTM D 3359)
Dolly Pull-Off (usando un testigo de adherencia de alineación fija
Tipo 3, ASTM D 4541)
Figura 43 Determinación de la adherencia mediante Dolly Pull-Off
Fuente: Propia
Pruebas de adherencia tales como éstas pueden usarse para investigar las fallas del
recubrimiento.
2.9.6. Discontinuidades (Holidays)
La detección de discontinuidades (holidays) se realiza para encontrar cortes, puntos
de alfiler y otros defectos o discontinuidades en la película. La corrección de los
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defectos en el recubrimiento es especialmente importante en algunas estructuras
como tanques diseñados para operar en inmersión y para tuberías enterradas.
Hay muchas causas de defectos de recubrimientos y algunos de los más frecuentes,
que dan lugar a discontinuidades incluyen, puntos de alfiler, escurrimientos y
colgamientos, cráteres y un espesor de película incorrecto.
Los tipos generales de estos equipos (Holiday Detector) incluyen:
Bajo Voltaje DC
Alto Voltaje DC
Alto Voltaje DC de Pulso
Alto Voltaje AC
Figura 44 Detección de discontinuidades mediante equipo de bajo voltaje DC
Fuente: Propia
2.10. Mantenimiento de sustratos en servicio
2.10.1. Operaciones de recubrimientos para mantenimiento
Las operaciones de recubrimientos para mantenimiento están definidas como la
aplicación de recubrimiento sobre un sustrato que ha sido instalado en su ambiente
final y ha sido puesto en servicio.
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Las operaciones de mantenimiento pueden ser para un sustrato con un recubrimiento
existente, o pueden ser el reemplazo de una sección del equipo o estructura. A
menudo la estructura o equipo que se recubrirá o reparará ha sido instalada en un
ambiente hostil y está sujeta a todos los tipos de contaminantes, tales como (pero no
limitados a) aceite, grasa, químicos, agua, etc.
Figura 45 Tanque de almacenamiento de dióxido de carbono (CO2)
Fuente: Propia
Generalmente, las operaciones de recubrimientos para mantenimiento se llevan a
cabo para mantener el sistema de recubrimientos de tal manera que éste continúe
proporcionando el grado de protección buscado originalmente y mejorar la apariencia
visual del sistema de recubrimientos.
2.10.2. Elementos de las operaciones de recubrimientos para mantenimiento
Una operación típica para un recubrimiento de mantenimiento puede variar desde un
sistema cuidadosamente diseñado para el mantenimiento industrial, hasta un esquema
de actividades aleatorias. Principalmente:
Selección del recubrimiento; debido a las muchas dificultades en situaciones de
recubrimientos de mantenimiento, se han impuesto algunas restricciones adicionales
para la selección de los recubrimientos, como elegir un recubrimiento compatible con
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el sistema de recubrimientos preexistentes y/o recubrimientos especiales que han sido
formulados para ser aplicado sobre una superficie que ha sido limpiada bajo
condiciones especiales.
Pre-inspección; antes de que se realice otro trabajo, la superficie deberá
inspeccionarse para localizar y marcar áreas con fallas que incluyan ampollas,
pérdida de adherencia, corrosión debajo de la película, caleamiento y áreas que han
sido contaminadas con grasas, sales químicas, suciedad u otras sustancias.
Preparación de la superficie; una vez que el área a ser reparada se haya localizado y
marcado, se pueden iniciar las operaciones de preparación de la superficie.
Se podrán encontrar muchas dificultades al obtener el grado de limpieza deseado en
la superficie, tales como:
Una gran acumulación de contaminantes (grasa, aceite, suciedad, sales químicas,
productos de corrosión, etc.).
Necesidad de limpiar y recubrir, mientras el equipo está en servicio.
Ciertos factores como las condiciones ambientales pueden influenciar el tiempo
en que la superficie retendrá la apariencia deseada por el estándar de limpieza.
Aplicación; La aplicación de los materiales por cualquier método es a la vez una
ciencia y un arte. Se necesita tanto de formación en clase y el entrenamiento en
campo para tener un aplicador que puede ser productivo y preciso. Tienen que ser
capaces de aplicar un recubrimiento con una tolerancia muy pequeña de espesor de
película, y hacerlo en condiciones muy adversas.
Inspección; evaluación de los estándares y pruebas para el control de calidad de la
aplicación e inspección final.
III. LIMPIEZA Y PREPARACIÓN SUPERFICIAL DEL ACERO MEDIANTE
CHORRO DE AGUA (WATERJETTING)
Contempla el uso de una corriente de agua de alta presión para desprender
recubrimientos existentes y para limpiar contaminantes en un sustrato antes de aplicar
el recubrimiento por lo que es ampliamente usado en trabajos de mantenimiento ya
que el chorro de agua no produce un perfil de anclaje sobre el sustrato de acero
exponiendo solamente el perfil de anclaje original del sustrato teniendo la ventaja de
disponer de agua adecuada en cantidades grandes y económicas, carencia de
contaminación de las áreas circundantes porque no hay ninguna partícula abrasiva,
carencia de polvo y riesgos de chispa.
3.1 Especificaciones para las operaciones de recubrimientos para
mantenimiento
Las especificaciones para las operaciones de recubrimientos para mantenimiento
pueden variar entre trabajo y trabajo, y dependen de:
La condiciones de la superficie a ser reparada, las cuales pueden variar desde un
sistema de recubrimiento perfectamente intacto, hasta una falla al 100% del
recubrimiento, lo que implica un deterioro total de la superficie.
Cierre (parada) de planta o inspección
Efectos sobre el personal de planta en el área
Restricciones en el presupuesto
Uso de personal interno o por contratación
Accesibilidad del área
Resultados deseados por el propietario
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Entonces, una especificación para un recubrimiento de mantenimiento puede exigir
desde la limpieza a mano puntual de áreas con fallas, hasta limpiar la superficie
entera hasta metal blanco, y aplicar un sistema de recubrimiento totalmente nuevo.
3.1.1. Procedimiento de trabajo para las operaciones de mantenimiento
Una vez establecido los requerimientos de la especificación para las operaciones de
mantenimiento, se procederá a realizar los trabajos en campo:
a) Monitoreo de las condiciones ambientales
Se debe registrar la temperatura ambiental, la temperatura de la superficie, la
humedad y el punto de rocío en el comienzo de cada turno y al final de la jornada
como mínimo de acuerdo al estándar ASTM E337-02 (2007).
Los trabajos de preparación de superficie se realizaran bajo condiciones ambientales
tales que:
La humedad relativa no sea mayor al 85% y,
La temperatura de superficie sea como mínimo 3°C por encima de la temperatura
de rocío.
b) Preparación de superficie
Se realizara una limpieza previa al sustrato mediante una limpieza con solvente y
detergente biodegradable para remover cualquier contaminante depositada para luego
eliminar los defectos de fabricación como soldaduras imperfectas, laminaciones,
hendiduras profundas, esquinas y bordes afilados, codos y ángulos afilados; los
cuales deberán corregirse mediante la utilización de herramientas de poder a metal
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desnudo o similar aceptable conforme a las recomendaciones del ingeniero de diseño.
Se puede utilizar como guía el estándar NACE RP0178.
Para los trabajos de preparación de superficie y la aplicación de un recubrimiento en
cuanto a la iluminación, la Guía Tecnológica N° 12 de la SSPC nos indica que se
requieren un mínimo de 215 candelas por metro (20 candelas por pie), recomendando
538 candelas por metro (50 candelas por pie).
Para la limpieza final y preparación superficial del sustrato se hará uso de la unidad
comercial para las operaciones con chorro de agua.
La unidad comercial de chorro de agua puede ser montada sobre una plataforma,
remolque, o camión y usualmente consiste de bombas, mangueras, unidad motora
(diesel, electricidad, etc.), y varias herramientas tales como pistolas, boquillas,
lancetas, etc. Las mangueras (de alta presión), conexiones de la manguera y el resto
del equipo, incluso la válvula de control de la boquilla, lancetas, y boquilla, deben
tener una resistencia mínima de 2.5 veces la capacidad de su máxima resistencia de
operación.
Figura 46 Unidad típica de chorro de agua
Fuente: Programa de inspectores de recubrimientos nivel 2 Manual del estudiante
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La tecnología está mejorando rápidamente en este ámbito y como tal, nuevas
maquinarias se están desarrollando para mejorar el sistema. Un nuevo equipo que se
ha desarrollado es una unidad robótica de chorro de agua. Es un vehículo de
limpieza que se adhiere mediante vacío, cables o imanes, a una superficie vertical,
horizontal o invertida. Esta unidad está controlada por un solo operador. Una de las
características únicas de esta máquina es que recolecta en exceso del 95% del agua,
así como de los recubrimientos y óxido (desechos generados). Esta unidad se utiliza
en superficies verticales tales como cascos de buques y tanques, en superficies
horizontales tales como cubiertas planas, y en superficies invertidas como el fondo
plano de embarcaciones. También funciona bien en las juntas de soldadura, placas de
refuerzo contra la fricción, juntas traslapadas y costuras remachadas, y se mueve
fácilmente en y alrededor de las camas de la quilla y otras obstrucciones comunes.
Figura 47 Unidad de chorro de agua robótica
Fuente: Aplicación de recubrimientos sobre flash rust en ambiente marino e
industrial, Ing. Fredy Vidal
El agua puede impulsarse a través de un chorro sencillo, un chorro en forma de
abanico, o múltiples chorros giratorios. Los chorros se rotan por pequeños motores de
aire, eléctricos o hidráulicos, incluso pueden ser rotados por los orificios ligeramente
inclinados de una boquilla de orificios múltiples.
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El chorro de agua se produce por orificios o puntas que vienen en diferentes formas.
Los chorros de forma redonda son los más comunes, pero se dispone de otras formas.
Un buen chorro de forma redonda se puede producir con 240 MPa (35,000 psig). Las
puntas pueden diseñarse para producir chorros múltiples de agua que normalmente
están girando para conseguir la mayor remoción posible. Los chorros de forma
redonda son cortadores, y los chorros de abanico son talladores y/o empujadores.
Normalmente se usan puntas de boquilla intercambiables para producir los flujos
deseados. Una velocidad de flujo de agua típica es de 4 a 53 L/min (1 a 14 gal/min).
Las máquinas envían una corriente concentrada de agua a través de una manguera y
boquillas a presiones de 70 a 414 MPa (10,000 a 60,000 psig); sin embargo, con la
tecnología actual, las presiones más prácticas son de 70 a 240 MPa (10,000 a 35,000
psig). El ángulo de la boquilla y su distancia a la superficie a limpiar se determina por
el tipo de materia a eliminar y el tipo de equipo usado. Aunque la distancia de la
boquilla a la superficie puede variar de 0.6 a 1 m (2 a 3 pies), típicamente la boquilla
deberá mantenerse de 5 a 25 cm (2 a 10 pulg) de la superficie.
Calidad del agua
El agua utilizada para el chorro de agua debe ser pura, estar libre de partículas sólidas
y de sedimentos para que no contamine al limpiar la superficie y evitar dañar al
equipo.
Se filtrará el agua utilizada usando filtros de 5μm o más pequeños. Se determinará la
cantidad de sales solubles en el agua utilizada haciendo uso del medidor de
conductividad siendo el valor máximo permitido el indicado en la especificación del
proyecto o el recomendado por el fabricante del recubrimiento (generalmente el valor
máximo de sales solubles en el agua es de 1000 µS/cm).
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Preparación superficial con chorro de agua
De acuerdo a los requerimientos establecidos para las operaciones de mantenimiento,
y la utilización del chorro de agua como medio de limpieza superficial, se definen los
tipos de waterjetting:
Tabla 1 Tipos de Waterjetting
Tipos de
Waterjetting
PSI MPa Flujo
(l/min)
Efectos del
WaterJetting
Baja presión
Water Cleaning
< 5000
< 34 Remueve
incrustaciones, sales y
suciedad
Alta presión
Water Cleaning
5000 a
10000
34 a 70 90 a 50 Remueve oxido y
recubrimiento
superficial. Queda
recubrimiento bien
adherido.
Alta presión
Water Jetting
10000 a
30000
70 a 210 50 a 25 Remueve óxido y
recubrimiento. Quedan
partes de recubrimiento
bien adherido.
Ultra Alta presión
Water Jetting
> 30000 > 210 Menos de
12
Remueve todo el
recubrimiento sobre
35000 psi. Queda
expuesto el perfil de
rugosidad original.
Fuente: Propia
Previo a los trabajos de preparación de superficie final, se deberá lavar la superficie
con agua dulce y detergente industrial biodegradable mediante lavado a presión para
eliminar grasas, aceites, sales provenientes de la atmósfera marina, productos
químicos (ácidos y alcalinos) y cualquier otro contaminante.
El grado de limpieza a obtener deberá estar de acuerdo a los requerimientos de
mantenimiento según los siguientes estándares:
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Tabla 2 Grados de limpieza para el waterjetting
GRADO DE LIMPIEZA DESCRIPCIÓN
SSPC-SP WJ-1 / NACE WJ-1 Limpieza a metal desnudo
SSPC-SP WJ-2 / NACE WJ-2 Limpieza muy exhaustiva
SSPC-SP WJ-3 / NACE WJ-3 Limpieza profunda
SSPC-SP WJ-4 / NACE WJ-4 Limpieza ligera o superficial
Fuente: Propia
Al término de la preparación superficial mediante chorro de agua, se procederá a
realizar la prueba de sales solubles en agua en la superficie preparada según el
estándar SSPC Guía 15, Métodos de Campo para la Extracción y Análisis de Sales
Solubles en Sustratos de Acero y Otros Sustratos no Porosos y la medición de las
sales solubles en agua por el método de conductividad siendo el valor máximo
aceptable de 16.7 µS/cm.
Se realizara la evaluación del perfil de anclaje original del acero preparado mediante
el método de operación de la cinta de réplica según estándar ASTM D 4417 Método
C para verificar que dicho perfil esté de acuerdo a los requerimientos para las
operaciones de recubrimientos de mantenimiento.
Se evaluará el grado de Flash Rust en la superficie metálica preparada según
Apéndice B, Métodos de evaluación del grado de flash rust (Prueba de frotamiento o
Prueba con cinta) del estándar de limpieza establecida y acorde a los requerimientos
para las operaciones de recubrimientos de mantenimiento.
Prueba de frotamiento; se sugiere el siguiente procedimiento para estandarizar la
cantidad de presión utilizada para llevar a cabo una prueba de limpieza en una
superficie de flash rust:
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(a) Cuidadosamente envuelva un paño de tejido blanco que no suelte pelusa
alrededor de una brocha de nylon estándar de 100 mm (4 in.), y mantenerlo en su
lugar de una manera que evite que la tela se deslice.
(b) Pase la brocha de nylon envuelto en tela a través de la superficie de flash rust en
un solo movimiento, use una presión equivalente a la utilizada para aplicar
pintura de casa a una puerta. La longitud del golpe debe ser coherente (por
ejemplo, un pase que cubre 150 mm [6 in.] de longitud).
(c) Retirar el paño blanco de la brocha y evaluar el color y la cantidad de óxido en la
tela. "Directrices recomendados para la Evaluación de Flash Rust," emitido por el
NSRP, proporciona una guía para llevar a cabo esta evaluación del flash rust.
Prueba con Cinta; La prueba de tracción de cinta es una modificación del método de
la cinta sensible a la presión en la norma ISO 8502 – 3. El procedimiento es el
siguiente:
(a) Elija una zona en la superficie del flash rust para realizar la prueba.
(b) Coloque un trozo de cinta de 50 mm (2 pulgadas) de largo (como se especifica en
la norma ASTM D 3359) en el área de prueba seleccionado y lo frota a fondo con
la yema del dedo (no una uña) para asegurarse de que la cinta se adhiera
firmemente. Luego pelar la cinta de la superficie y lo coloca en un pedazo de
papel blanco para referencia.
(c) Repita el procedimiento en (b) nueve veces (para un total de 10 veces) con un
nuevo pedazo de cinta aplicada a un mismo punto en la superficie (área de
prueba seleccionado) cada vez.
(d) Evaluar la apariencia de la décima cinta (10ma
cinta) y la apariencia de la zona de
pruebas en la superficie del flash rust después del retiro de la décima cinta
acuerdo con la Tabla.
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Tabla 3 Grado de flash rust después del retiro de la 10ma
cinta
Grado de
Flash Rust
Apariencia de 10ma cinta
(después de retirar de la zona
de ensayo)
Apariencia del área de ensayo
(después de retirar 10ma cinta)
Ligero No hay óxido sobre la cinta Sin cambios o solo un ligero
cambio en la apariencia del área
de ensayo.
Moderado Ligero, óxido marrón-rojizo
localizado sobre la cinta
Cambio significativo en la
apariencia del área de ensayo,
muestra zonas localizadas de
óxido negro.
Pesado Significativo, óxido marrón-
rojizo uniforme sobre la cinta,
además muestra granos de óxido
negro
Cambio significativo en la
apariencia del área de ensayo,
muestra áreas localizadas de
óxido negro.
Fuente: Propia
c) Aplicación de recubrimientos
No podrán realizarse trabajos de aplicación cuando las condiciones de temperatura y
humedad relativa del ambiente estén fuera de los rangos recomendados en las hojas
técnicas de los productos, debido a posibles fallas de ampollamiento,
desprendimiento, porosidad u otro defecto que disminuya la vida útil normal del
recubrimiento.
Las superficies que se pinten deberán ser protegidas hasta el máximo practicable
contra los efectos de la lluvia, la condensación y la contaminación hasta que la capa
del recubrimiento se encuentre seca. Cuando el espesor especificado del
recubrimiento medido según estándar SSPC – PA2, Procedure for determining
conformance to dry coating thickness requirements, no sea obtenido mediante la
aplicación de una capa, deberán aplicarse capas subsiguientes, hasta que se obtenga el
espesor indicado en las especificaciones, estas no podrán efectuarse sino hasta que la
anterior se encuentre completamente seca y limpia para su aplicación.
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El espesor aplicado por cada capa no deberá afectar la apariencia ni las propiedades
y/o la vida útil del recubrimiento.
Después de cada aplicación de recubrimientos, se revisará la película final de acuerdo
a lo recomendado en las especificaciones de pintado. Todo el recubrimiento deberá
aplicarse de tal forma que el acabado sea uniforme en cuanto al color, textura y apa-
riencia.
d) Inspección final de los recubrimientos
El acabado final de la aplicación de los recubrimientos deberá estar libre de pinholes,
arrugas, craqueos o fisuras. Cualquier deficiencia en estos aspectos, deberá ser
corregida en campo.
Las pruebas de campo realizadas para tal fin y según la especificación del proyecto
para el mantenimiento son:
Prueba de adhesión (estándar de desprendimiento ASTM D 4541 y/o estándar de
Corte Cruzado ASTM D 3359), si está permitido, se pueden realizar para
determinar la fuerza adhesiva de los recubrimientos hacia el sustrato, y la unión
entre los recubrimientos viejos y nuevos.
Prueba de detección de discontinuidades, el estándar NACE RP0188 puede ser
consultado dependiendo de los requerimientos de la especificación, tipo de
recubrimiento y sustrato.
3.2. Pintado de mantenimiento con preparación Waterjetting UHP
Para el proyecto en mención se realizaron trabajos que se enfocaron en la preparación
de superficie por chorro de Agua a Ultra Alta Presión (Waterjetting UHP) y
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aplicación de un sistema de pintado industrial, siguiendo estrictamente
procedimientos, normas y recomendaciones con la calidad necesaria para asegurar la
protección de los activos los cuales estarán expuestos a atmósferas corrosivas de
clasificación C5–M (ISO 12994–2) es decir, zona industrial con elevada humedad y
atmósfera agresiva, debido a contaminación posible de vapores de SO2 y SO3, con
cercanía al mar, durante el periodo de servicio del proyecto en mención.
3.2.1. Aspectos Previos
Se realizará trabajos de mantenimiento a la superficie exterior de 3 tanques de
almacenamiento estando éstos en servicio y posicionados en la zona de
almacenamiento expuesto al medio ambiente y que por motivos de seguridad está
prohibido la utilización de material abrasivo (arena, escoria de cobre, granalla
metálica u algún otro material) para la preparación superficial del acero por riesgo de
explosividad, generación de polución que pueda dañar y/o atascar instrumentos de
medición y daños a la salud del personal en general.
Tabla 4 Característica de los Tanques de Almacenamiento
Tanque Producto Diámetro
(m)
Altura
(m)
Material Capacidad
(m3)
Tiempo
de
servicio
306 Butyl Glicol 7.64 12.00 Acero al Carbono
A36
549.84 5 años
307 Butilo 7.64 12.00 Acero al Carbono
A36 549.84 5 años
308 n-Propanol 8.25 12.00 Acero al Carbono
A36 643.48 5 años
Fuente: Propia
Las condiciones del material, según evaluación del grado de corrosión de los tanques
de almacenamiento se indican a continuación:
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Evaluación del Grado de Corrosión:
Cilindro externo de los tanques
La presencia de corrosión en cordones de soldadura, bordes, esquinas, filos, zonas de
difícil acceso se originan como consecuencia de la tensión superficial del
recubrimiento; el cual, durante su aplicación tiende a encogerse o retraerse,
originando zonas con EPS (espesores de película seca) relativamente bajos.
La corrosión de las planchas del cilindro, techo y escaleras del tanque, puede deberse
por bajos espesores de la película seca en un ambiente corrosivo característico de la
zona. La cantidad de corrosión no excede el 10% del área total evaluada.
El tizamiento (caleamiento) ligero registrado en la superficie exterior del tanque se
debe a la interacción de los rayos UV del Sol, los cuales tienden a degradar la resina,
originando: pérdida del brillo, decoloración y/o variación en el color del
recubrimiento.
Según diagnostico obtenido por la evaluación del recubrimiento y las limitaciones
presentadas por motivos de seguridad, se opta por lo siguiente:
Preparación de superficie (Mantenimiento Menor: % corrosión <10%)
Limpieza de superficie con recubrimiento en servicio
La superficie deberá estar libre de grasa, aceites y otros materiales contaminantes, así
como de defectos de construcción, imperfecciones de soldadura, salpicaduras de
escoria de soldadura, filos y puntas cortantes, los que deberán ser eliminados con
herramientas mecánicas y motrices (disco de desbaste).
Para efectuar trabajos de repintado y mantenimiento, previo a los trabajos de
preparación de superficie, se deberá lavar la superficie con agua dulce y detergente
industrial biodegradable) con equipo de hidrolavado de alta presión (> 34 Mpa ó
3,000 psi); para eliminar restos de productos derivados de petróleo, grasas, sales
90
provenientes de la atmósfera marina, productos químicos (ácidos y alcalinos) y
cualquier otro contaminante.).
Repintado general: Superficies con recubrimiento en servicio
En áreas localizadas con corrosión, la preparación de superficie, se efectuará con
Waterjetting UHP a presión de trabajo > 315 Mpa ó 45,000 psi, hasta metal desnudo.
El grado de limpieza deberá ser WJ-1 (Limpieza a metal Desnudo).
En áreas con recubrimiento antiguo en servicio, la preparación de superficie, se
efectuará con Waterjetting UHP a presión de trabajo > 210 Mpa ó 30,000 psi).
El grado de limpieza deberá ser WJ-4 (Limpieza Ligera o superficial).
La superficie deberá estar libre de recubrimiento antiguo mal adherido, recubrimiento
desintegrado por efecto del tiempo de servicio, etc.
Pintado de mantenimiento: Limpieza general a metal desnudo
La preparación de superficie, se efectuará con Waterjetting UHP a presión de trabajo
> 315 Mpa ó (45,000 psi, con chorro de agua a UHP presión hasta metal desnudo.
El grado de limpieza deberá ser: WJ-1 (Limpieza a metal Desnudo).
Contaminantes no visibles (Sales Solubles)
La prueba del contenido de sales totales, se efectuará en la superficie después del
proceso de limpieza con Waterjetting UHP y no deberá exceder de: 16.7 μS/cm . La
extracción de los contaminantes, se efectuará por Método Parche de Látex y la
medición del contenido de sales totales se efectuará con el conductímetro.
3.2.2. Normas y Equipos Usados
Las normas que aplican son:
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SSPC VIS4/NACE VIS 7 Guía y referencia fotográfica para superficies de
aceros preparados por Waterjetting.
SSPC WJ1/NACE WJ1 Limpieza a Metal Desnudo
SSPC WJ4/NACE WJ4 Limpieza Superficial o Ligera
SSPC SP1 Limpieza con solventes.
SSPC SP2 Limpieza con herramientas manuales.
SSPC SP3 Limpieza con herramientas de poder.
SSPC PA1 Pintado de acero para taller, campo y
mantenimiento.
ASTM D4417–C Determinación del perfil de anclaje (rugosidad)
del acero.
ASTM E337 Medición de condiciones ambientales.
ASTM D4414 Medición de espesores de película húmeda
(EPH) de la pintura.
SSPC PA2 Medición de espesores de película seca (EPS)
de la pintura.
ISO 8502–6 Medición del nivel de contaminantes no visibles
sobre la superficie (sales solubles en agua,
Método Bresle).
ASTM D 4541 Prueba de adherencia por tracción
Los equipos de inspección que se utilizaron fueron los siguientes:
Psicrómetro y termómetro de contacto, para la evaluación de las condiciones
ambientales.
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Medidor digital de EPS marca Elcometer 456, para la medición de los espesores
de película seca de los recubrimientos.
Conductímetro marca Horiba / Hanna, para la determinación de la conductividad
de las sales totales en el agua y en la superficie limpiada por waterjetting.
Micrómetro marca Mitutoyo, para la determinación del perfil de anclaje del
acero.
Medidor de EPH (galleta), para la medición de los espesores de película húmeda.
Equipo Hidráulico de Tracción marca Elcómeter 108, dollies de prueba
normados y pegamento de cianocrilato marca 3M, para la prueba de adherencia
por tracción.
Para la preparación de superficie se utilizaron los siguientes equipos:
Unidad típica de Chorro de Agua con boquillas intercambiables (boquillas para
chorros de forma redonda para las zonas con corrosión y boquillas para chorros de
abanico para el recubrimiento envejecido).
Compresor de 750 CFM.
Para la aplicación de los recubrimientos se utilizaron los siguientes equipos:
Equipo Airless neumático.
Equipo Airless eléctrico.
Equipos convencional de succión.
Brochas marca Tumi.
3.2.3. Preparación de Superficie y Sistema de Pintado
La preparación de superficie especificada fue según como se indica en la Tabla 5:
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Tabla 5 Grado de Preparación de Superficie
Condiciones
Iniciales
Superficie Norma Grado Descripción
Sin Grasa y/o
aceite
Cordones de soldadura
y zonas aleatorias con
corrosión
SSPC WJ-1 Limpieza a Metal Desnudo
Sin Grasa y/o
aceite
Recubrimiento en
servicio
SSPC WJ-4 Limpieza Ligera o
Superficial
Fuente: Propia
El sistema de pintado especificado y/o recomendado fue según la Tabla 4.3:
Tabla 6 Sistema de Pintado
Nº de Capa Recubrimiento EPS (mils)
1ra Epoxy Fenalcamina (*)
(tolerante a la humedad)
3 – 4
2da Epoxy Poliamida (*) (**) 5 – 6
3ra Poliuretano Acrílico Alifático 2 – 3
EPS Total 10 - 13
EPS: Espesor de Película Seca
Fuente: Propia
(*) Resanado y desmanchado general con Epoxy Fenalcamina en áreas donde se llegó
al metal y Epoxy Poliamida, hasta alcanzar espesor de película seca mínimo de 8
mils.
(**) Aplicación general de Epoxy Poliamida, para optimizar adhesión del Poliuretano
Acrílico Alifático.
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3.2.4. Resultados y Discusiones
a) Calidad del Agua
La conductividad de las sales totales en el agua utilizada para la preparación de
superficie por chorro de Agua (Waterjetting) al inicio de la obra no excedió los 1000
µS/cm recomendados por la Especificación del Proyecto y recomendaciones del
fabricante, siendo el valor obtenido mediante la prueba igual a 483 µS/cm.
Figura 48 Valor de conductividad de Sales Solubles en el Agua Utilizada
Fuente: Propia
b) Perfil de Anclaje
Durante la ejecución del proyecto, los resultados del perfil de anclaje (rugosidad)
expuestos del sustrato original estaban entre 2.5 y 3.0 mils, el cual aseguraba una
buena adherencia entre el sustrato y el sistema de pintado.
95
Figura 49 Medición del perfil de Anclaje según estándar ASTM D 4417 Método C
Fuente: Propia
Figura 50 Valor del perfil de Anclaje mediante micrómetro
Fuente: Propia
c) Condiciones Ambientales
Durante la ejecución del proyecto, las condiciones ambientales fueron óptimas. En la
Tabla 7 indica el resumen de lo mencionado en los días de preparación superficial y
aplicación de los recubrimientos:
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Tabla 7 Resumen de Condiciones Ambientales
Condiciones
ambientales
Mínimo Máximo
ΔT (Tsup – Tr), °C 3 10
Hr, % 65 85
ΔT = Diferencia de temperaturas (°C)
Tsup = Temperatura de superficie (°C)
Tr = Temperatura de Punto de rocío (°C)
Hr = Humedad relativa (%)
Fuente: Propia
d) Preparación de Superficie
Durante la ejecución del proyecto, se procedió con la siguiente preparación de
superficie:
Pre – Limpieza
Se procedió a lavar con agua y detergente biodegradable industrial, según norma
SSPC SP1, y luego enjuagar con abundante agua potable de baja conductividad para
remover contaminación superficial impregnada con suciedad, aceites y/o grasas.
Figura 51 Remoción de contaminantes Superficiales mediante lavado
Fuente: Propia
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En caso hubiera presencia de soldadura, bordes afilados, se procedía con una limpieza
con herramientas manuales / mecánicas, según norma SSPC SP2 / SP3.
Limpieza
La limpieza alcanzada fue por chorro de Agua a Ultra Alta Presión (Waterjetting
UHP), según norma SSPC SP WJ-1 / NACE WJ-1 (Limpieza a Metal Desnudo) sobre
las zonas con presencia de corrosión (cordones de soldadura y zonas puntuales) y
SSPC SP WJ-4 / NACE WJ-4 (Limpieza Ligero o Superficial) a las zonas con
recubrimiento en servicio, de acuerdo a lo establecido en la especificación y en el
procedimiento de pintado entregado al inicio del proyecto.
Se trabajaron con presiones que superaron los 50000 psi para alcanzar el nivel de
limpieza a metal desnudo en las zonas con óxido y a presiones que superaron los
30000 psi para alcanzar la limpieza ligera o superficial en el recubrimiento
envejecido debido a las condiciones de funcionamiento (eficiencia de la bomba para
el control de la presión durante la operación, pérdidas de presión debido a las
extensiones a la manguera para trabajar en altura, boquillas desgastadas utilizadas que
disminuían el efecto cortante del chorro de agua de forma redonda, limitaciones en
cuanto a la distancia y ángulo de limpieza sobre la superficie ya que la operación se
realizaba en andamios colgantes, fatiga del operador de la boquilla debido al impacto
de empuje por la propia presión del agua).
La tasa de flujo de agua fue de 40 L/min consumiéndose un total de 4800 L de agua
para un tiempo neto de 2 horas de limpieza por tanque (ver figura 52).
Post – Limpieza
Previo a la aplicación del sistema de pintado se eliminó el residuo del polvo, arena y
material suelto así como también a ayudar a la evaporación de la humedad de la
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superficie usando aire seco a presión y la realización de los controles de
aseguramiento de la calidad como:
Figura 52 Limpieza superficial mediante Chorro de Agua (Waterjetting)
Fuente: Propia
Nivel de Flash Rust: Se determinó que el nivel de Flash Rust se encontraba en el
grado Ligero con decoloración amarillenta sobre la superficie limpiada.
Figura 53 Flash Rust sobre la superficie limpiada
Fuente: Propia
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Determinación de Sales Solubles sobre la superficie: Se realizó la determinación
de las sales solubles sobre la superficie exterior limpiada mediante chorro de Agua,
obteniéndose como resultado el valor de 13 µS/cm, estando el valor dentro del rango
especificado para el proyecto y recomendado por el fabricante ( valor máximo
permitido 16.7 µS/cm).
Figura 54 Extracción de las sales solubles método del Parche de Latex
Fuente: Propia
Figura 55 Valor de la conductividad de las sales solubles en agua
Fuente: Propia
100
e) Aplicación del Sistema de Pintado
Durante la ejecución del proyecto, se procedió de la siguiente manera:
Preparación del Recubrimiento
Se realizó una adecuada mezcla y homogenización de los componentes así como el
porcentaje de dilución requerida y la filtración del recubrimiento preparado para
evitar el paso de contaminantes que pudieran perjudicar el equipo o la aplicación.
Aplicación de los Recubrimientos
Las aplicaciones se realizaron de forma diferente para cada capa del sistema de
pintado de acuerdo a las recomendaciones del fabricante, especificación del proyecto
y Hojas Técnicas del producto.
Debido a que el proceso de limpieza con chorro de agua humedece el ambiente y la
superficie preparada, se utilizó como capa base un recubrimiento Epoxy
Fenalcamina como recubrimiento especial tolerante a la humedad (superficies
húmedas).
Los recubrimientos Epoxy Fenalcamina tienen propiedades de curado a bajas
temperaturas. Debido a estas características, las fenalcaminas están siendo
ampliamente utilizadas en la marina, mantenimiento industrial y aplicaciones de
ingeniería civil. Los resultados obtenidos con resinas de fenalcamina demuestran las
siguientes propiedades: curado a baja temperatura (tan bajo como 35 °F),
proporciones de mezcla no críticas, excelente resistencia al agua, buena flexibilidad,
buena compatibilidad con diferentes tipos de resinas epoxy, buena adhesión a
superficies poco preparados y una amplia gama de otras características interesantes
que deriva de su estructura.
101
La larga cadena lateral lineal de fenalcaminas proporciona a la resina una alta
hidrofobicidad que reduce el efecto de hidroxilo fenólico en la sensibilidad al agua
lo cual lo hace resistente a la humedad. Estas son propiedades clave para
recubrimientos y adhesivos en la industria de sellador. Cuanto mayor sea la
resistencia al agua y agua de mar, menos posibilidades se tendrá de que el aglutinante
de la resina se quiebre. El producto tendrá una mejor adherencia, una mejor
protección a la corrosión y una mejor capacidad de vincularse al sustrato por lo que a
mayor viscosidad de la fenalcamina, mejor es la resistencia al agua (ver anexo 16).
Medición de Espesores de Película Seca
Las mediciones de los espesores de película seca (EPS) se realizaron con la ayuda de
un medidor digital de marca Elcometer 456 en cada etapa de la operación y de
acuerdo con la especificación del proyecto.
Inspección Final de los Recubrimientos
Se realizaron las pruebas de adhesión según estándar ASTM D 4541 luego de que el
recubrimiento haya alcanzado su tiempo de curado completo obteniéndose valores
por encima del mínimo especificado y recomendado por el fabricante (valor mínimo
aceptado para sistemas epoxicos – poliuretanos 700 Psi).
Dichas pruebas se realizaron en probetas (planchas testigo de 30cm x 30 cm x 0.6
cm) preparada con el mismo sistema de pintado especificado y bajo las mismas
condiciones de preparación superficial y durante el proceso de aplicación del sistema
de recubrimientos en los tanques.
Los resultados de la prueba se detallan en la Tabla 8:
102
Tabla 8 Pruebas de Adhesión por Tracción
Nº de
Pruebas
Superficie EPS
(mils)
Valor en
PSI.
Tipo de
desprendimiento
Prueba 1 Probeta 12.35 1500 2%A/B, 70%C,
28%Y
Prueba 2 Probeta
13.07 1500 90%B/C, 7%Y,
3%Y/Z
Prueba 3 Probeta 11.98 1800 2%A/B, 92%C, 6%Y
Fuente: Propia
Denominación del sustrato, capas, pegamento y dispositivos:
A = Sustrato
B = 1era capa
C = 2da capa
D = 3ra capa
Y = Pegamento
Z = Dispositivo de arranque ó dolly
Clasificación según el tipo de desprendimiento:
“B”, fallo cohesivo de la primera capa.
“C”, fallo cohesivo de la segunda capa.
“D”, fallo cohesivo de la tercera capa.
“A/B”, fallo adhesivo entre el sustrato y la primera capa.
“B/C”, fallo adhesivo entre la primera y segunda capa.
“C/D”, fallo adhesivo entre la segunda y tercera capa.
“D/Y”, fallo adhesivo entre pegamento y tercera capa.
“Y”, fallo cohesivo del pegamento.
“Y/Z”, fallo adhesivo entre el pegamento y el dolly.
103
Figura 56 Valor de la Presión de ruptura en Psi.
Fuente: Propia
IV. CONCLUSIONES Y RECOMENDACIONES
4.1. CONCLUSIONES
1. De acuerdo a los resultados obtenidos se concluye que la protección al sustrato
dado por el sistema de pintado para el casco externo del tanque de
almacenamiento está asegurado. Esto se demuestra gracias a la excelente
adherencia que existe entre el sistema de recubrimientos con el sustrato, las
mismas que en promedio están por encima de los 1500 Psi para el sistema
externo.
2. Se debe considerar que las condiciones de operación fueron las adecuadas y bajo
las condiciones de preparación de superficie especificados (Limpieza a Metal
Desnudo y Grado de Flash Rust Ligero), estos aspectos definitivamente
intervinieron en los resultados finales. Así mismo, mínimamente se observó
desprendimientos que van hasta el sustrato; en general los desprendimientos
fueron del tipo adhesivo de la última capa con el pegamento, esto nos permite
asegurar que los sistemas protegerán por efecto barrera quedando el
recubrimiento muy fuertemente adherido aun cuando pueda haber daños
superficiales por manipuleo, transporte, montaje o de condiciones de operación.
4.2. RECOMENDACIONES
1. A presiones de 234 a 248 MPa (34,000 a 36,000 psig), se obtiene un acabado
mate uniforme que rápidamente cambia a un color de tono dorado a no ser que se
agregue un inhibidor o se use un deshumidificador. Se remueve materia
superficial incluyendo gran parte de calamina. Generalmente, se requiere más
tiempo para remover calamina fuertemente adherida.
105
2. En algunos casos con UHP WJ, la distancia de la boquilla de la superficie deberá
ser de sólo 6 a 13 mm (0.25 a 0.5 pulgadas).
3. Cuando se remuevan laminaciones pesadas de óxido o recubrimientos
preexistentes, la boquilla deberá mantenerse a 5 cm (2 pulg) de la superficie, casi
perpendicular (90 grados) de la superficie.
4. Para mejores resultados cuando se remueva epóxicos de altos sólidos, la boquilla
deberá mantenerse a 45 grados respecto a la superficie.
5. Para minimizar la fatiga del operador y asegurar una operación segura, el
operador de boquilla deberá alternar posición con otro operador a intervalos
designados, dependiendo del equipo y las presiones utilizados.
6. Generalmente, si se emplea Ultra Alta Presión, con un volumen reducido de
agua, se producirá un menor impacto de empuje por la propia presión de agua y,
por lo tanto, menos fatiga para el operador.
V. BIBLIOGRAFÍA
1. Domingos, Fabio Ph.D., La Prevención de la Corrosión en Estructuras Metálicas.
Páginas 17, 19, 20.
2. Fitzsimons, Brendan. Visual Comparison Manual – Application and Coating
Defects. Páginas 42, 43, 52, 64. Año 1997-1998.
3. NACE International, Programa de Inspectores de Recubrimiento Nivel 1 Manual
del Estudiante. Capítulos 2, 10 y 20. Agosto 2010.
4. NACE Internacional, Programa de Inspectores de Recubrimientos Nivel 2
Manual del Estudiante. Capítulos 2, 7, 22. Enero 2011.
5. McNail, M (Summer 2013). New Waterjetting Standars Replace Withdrawn
NACE N° 5. Inspect This!. Consultado el 12 de Marzo de 2014. Disponible en
http://www.nace.org/uploadedFiles/Publications/Newsletters/InspectThis/Inspect
This_Summer2013.pdf
6. NACE International (2002). Corrosion Cost and Preventive Strategies in the
United States. Nace. Consultado el 21 de Junio de 2014. Disponible en
http://www.nace.org/uploadedFiles/Publications/ccsupp.pdf
7. Preguntale a Sherwin (2011). Chorro abrasivo: excelente técnica para limpiar
superficies. Preguntale a Sherwin. Consultado el 3 Julio de 2014. Disponible en
http://www.preguntaleasherwin.cl/2011/chorro-abrasivo-excelente-tecnica-para-
limpiar-superficies/
VI. ANEXOS
ANEXO 1: SSPC – VIS4/ NACE VIS 7: Guide and Reference Photographs for
Steel Surfaces Prepared by Waterjetting
ANEXO 2: SSPC – SP1: Solvent Cleaning
ANEXO 3: SSPC – SP2: Hand Tool Cleaning
ANEXO 4: SSPC – SP3: Power Tool Cleaning
ANEXO 5: SSPC – SPWJ-1/NACE WJ1: Waterjet Cleaning of Metals-Clean
to Bare Substrate (WJ-1)
ANEXO 6: SSPC – SPWJ-4/NACE WJ4: Waterjet Cleaning of Metals-Light
Cleaning (WJ-4)
ANEXO 7: ASTM E337: Standard Test Method for Measuring Humidity with
a Psychrometer (the Measurement of Wet- and Dry-Bulb
Temperatures).
ANEXO 8: ASTM D4414: Standard Practice for Measurement of Wet Film
Thickness by Notch Gages
ANEXO 9: ASTM D4417: Field Measurement of Surface Profile of Blast
Cleaned Steel – Method C.
ANEXO 10: SSPC Guide 15: Field Methods for Retrieval and Analysis of
Soluble Salts on Steel and Other Nonporous Substrates.
ANEXO 11: ASTM D4541: Standard Test Method for Pull-Off Strength of
Coatings Using Portable Adhesion Testers.
ANEXO 12: SSPC PA1: Shop, Field, and Maintenance Painting of Steel
ANEXO 13: SSPC PA2: Procedure for Determining Conformance to Dry
Coating Thickness Requirements
ANEXO 14: ISO 12944 – Part 2: Classification of environments.
ANEXO 15: ISO 8502 Part 6: Extraction of soluble contaminants for analysis –
The Bresle method
ANEXO 16: PHENALKAMINE Multipurpose Epoxy Resin Curing Agents
SSPC-SP 1November 1, 1982
Editorial Revisions November 1, 2004
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SSPC: The Society for Protective Coatings
SURFACE PREPARATION SPECIFICATION NO. 1Solvent Cleaning
1. Scope
1.1 This specification covers the requirements for the solvent cleaning of steel surfaces.
2. Definition
2.1 Solvent cleaning is a method for removing all visible oil, grease, soil, drawing and cutting compounds, and other soluble contaminants from steel surfaces.
2.2 It is intended that solvent cleaning be used prior to the application of paint and in conjunction with surface prepara-tion methods specified for the removal of rust, mill scale, or paint.
3. Surface Preparation Before and After Solvent Cleaning
3.1 Prior to solvent cleaning, remove foreign matter (other than grease and oil) by one or a combination of the following: brush with stiff fiber or wire brushes, abrade, scrape, or clean with solutions of appropriate cleaners, provided such cleaners are followed by a fresh water rinse.
3.2 After solvent cleaning, remove dirt, dust, and other contaminants from the surface prior to paint application. Ac-ceptable methods include brushing, blow off with clean, dry air, or vacuum cleaning.
4. Methods of Solvent Cleaning
4.1 Remove heavy oil or grease first by scraper. Then remove the remaining oil or grease by any of the following methods:
4.1.1 Wipe or scrub the surface with rags or brushes wet-ted with solvent. Use clean solvent and clean rags or brushes for the final wiping.
4.1.2 Spray the surface with solvent. Use clean solvent for the final spraying.
4.1.3 Vapor degrease using stabilized chlorinated hydro-carbon solvents.
4.1.4 Immerse completely in a tank or tanks of solvent. For the last immersion, use solvent which does not contain detrimental amounts of contaminant.
4.1.5 Emulsion or alkaline cleaners may be used in place of the methods described. After treatment, wash the surface with fresh water or steam to remove detrimental residues.
4.1.6 Steam clean, using detergents or cleaners and follow by steam or fresh water wash to remove detrimental residues.
5. Inspection
5.1 All work and materials supplied under this standard shall be subject to timely inspection by the purchaser or his authorized representative. The contractor shall correct such work or replace such material as is found defective under this standard. In case of dispute the arbitration or settlement procedure established in the procurement documents, if any, shall be followed. If no arbitration or settlement procedure is established, then a procedure mutually agreeable to purchaser and contractor shall be used.
5.2 The procurement documents covering work or purchase should establish the responsibility for testing and for any re-quired affidavit certifying full compliance with the standard.
6. Disclaimer
6.1 While every precaution is taken to ensure that all information furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, coatings, or methods specified herein, or of the specification or standard itself.
6.2 This specification does not attempt to address prob-lems concerning safety associated with its use. The user of this specification, as well as the user of all products or practices described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.
7. Note
Notes are not requirements of this specification.
7.1 A Commentary Section is available and contains ad-ditional information and data relative to this specification. The Surface Preparation Commentary, SSPC-SP COM, is not part
SSPC-SP 2November 1, 1982
Editorial Revisions November 1, 2004
2-57
SSPC: The Society for Protective Coatings
SURFACE PREPARATION SPECIFICATION NO. 2Hand Tool Cleaning
1. Scope
1.1 This standard covers the requirements for hand tool cleaning steel surfaces.
2. Definitions
2.1 Hand tool cleaning is a method of preparing steel surfaces by the use of non-power hand tools.
2.2 Hand tool cleaning removes all loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter. It is not intended that adherent mill scale, rust, and paint be removed by this process. Mill scale, rust, and paint are consid-ered adherent if they cannot be removed by lifting with a dull putty knife.
2.3 SSPC-VIS 3 or other visual standard of surface prepa-ration agreed upon by the contracting parties may be used to further define the surface (see Note 8.1).
3. Referenced Standards
3.1 The latest issue, revision, or amendment of the refer-enced standards in effect on the date of invitation to bid shall govern, unless otherwise specified. Standards marked with an asterisk (*) are referenced only in the Notes, which are not requirements of this standard.
3.2 If there is a conflict between the requirements of any of the cited reference standards and this standard, the require-ments of this standard shall prevail.
3.3 SSPC SPECIFICATIONS:
SP 1 Solvent Cleaning* SP 3 Power Tool Cleaning* SP 11 Power Tool Cleaning to Bare
Metal* SP 15 Commercial Grade Power Tool
Cleaning VIS 3 Guide and Reference Photographs
for Steel Surfaces Prepared by for Power- and Hand-Tool Cleaning
3.4 INTERNATIONAL ORGANIZATION FOR STANDARD-IZATION (ISO):
* 8501-1 Preparation of steel substrates before appli-cation of paints and related products: Visual assessment of surface cleanliness—Part I.
4. Surface Preparation Before and After Hand Tool Cleaning
4.1 Before hand tool cleaning, visible deposits of oil, grease, or other materials that may interfere with coating adhesion shall be removed in accordance with SSPC-SP 1 or other agreed-upon methods. Nonvisible surface contaminants such as soluble salts shall be treated to the extent specified by the procurement documents [project specifications] (see Note 8.2).
4.2 After hand tool cleaning and prior to painting, reclean the surface if it does not conform to this standard.
4.3 After hand tool cleaning and prior to painting, remove dirt, dust, or similar contaminants from the surface. Accept-able methods include brushing, blow off with clean, dry air, or vacuum cleaning.
5. Methods of Hand Tool Cleaning
5.1 Use impact hand tools to remove stratified rust (rust scale).
5.2 Use impact hand tools to remove all weld slag.
5.3 Use hand wire brushing, hand abrading, hand scrap-ing, or other similar non-impact methods to remove all loose mill scale, all loose or non-adherent rust, and all loose paint.
5.4 Regardless of the method used for cleaning, if specified in the procurement documents, feather the edges of remaining old paint so that the repainted surface can have a reasonably smooth appearance.
5.5 If approved by the owner, use power tools or blast cleaning as a substitute cleaning method for this standard.
SSPC-SP 2November 1, 1982Editorial Revisions November 1, 2004
2-58
6. Inspection
6.1 Unless otherwise specified in the procurement docu-ments, the contractor or material supplier is responsible for quality control to assure that the requirements of this document are met. Work and materials supplied under this standard are also subject to inspection by the purchaser or an authorized representative. Materials and work areas shall be accessible to the inspector.
6.2 Conditions not complying with this standard shall be corrected. In the case of a dispute, an arbitration or settlement procedure established in the procurement documents (project specification) shall be followed. If no arbitration or settlement procedure is established, then a procedure mutually agree-able to purchaser and material supplier (or contractor) shall be used.
7. Disclaimer
7.1 While every precaution is taken to ensure that all in-formation furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, coatings, or methods specified herein, or of the specification or standard itself.
7.2 This standard does not attempt to address problems concerning safety associated with its use. The user of this stan-dard, as well as the user of all products or practices described
herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.
8. Notes
Notes are not requirements of this standard.
8.1 Note that the use of visual standards in conjunction with this standard is required only when they are specified in the procurement documents (project specification) covering the work. It is recommended, however, that the use of visual stan-dards be made mandatory in the procurement documents. SSPC-VIS 3 provides a suitable comparative visual stan-dard for SSPC-SP 2, SSPC-SP 3, SSPC-SP 11, and SSPC-SP 15. ISO 8501-1 may also serve as a visual standard.
8.2 The SSPC Surface Preparation Commentary (SSPC-SP COM) contains additional information and data relevant to this specification. The Commentary is non-mandatory and is not part of this specification. The table below lists the subjects discussed relevant to hand tool cleaning and the appropriate Commentary Section.
Subject Commentary SectionFilm Thickness ................................................. 10Maintenance Painting ...................................... 4.2Rust, Stratified Rust, Pack Rust, and Rust Scale .......................... 4.3.1Visual Standards .............................................. 11Weld Spatter ................................................. 4.4.1
SSPC-SP 1November 1, 1982Editorial Revisions November 1, 2004
2-56
of this specification. The table below lists the subjects discussed relevant to solvent cleaning and the appropriate Commentary section.
Section Subject SSPC-SP COM Section
Solvents and Cleaners .................... 5.1.1 through 5.1.3Steam Cleaning ......................................................5.1.4Threshold Limit Values ...........................................5.1.5
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SSPC-SP 3November 1, 1982
Editorial Revisions November 1, 2004
SSPC: The Society for Protective Coatings
SURFACE PREPARATION SPECIFICATION NO. 3Power Tool Cleaning
1. Scope
1.1 This standard covers the requirements for power tool cleaning of steel surfaces.
2. Definition
2.1 Power tool cleaning is a method of preparing steel surfaces by the use of power assisted hand tools.
2.2 Power tool cleaning removes all loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter. It is not intended that adherent mill scale, rust, and paint be removed by this process. Mill scale, rust, and paint are consid-ered adherent if they cannot be removed by lifting with a dull putty knife.
2.3 SSPC-VIS 3 or other visual standard of surface prepa-ration agreed upon by the contracting parties may be used to further define the surface (see Note 8.1).
3. Referenced Standards
3.1 The latest issue, revision, or amendment of the refer-enced standards in effect on the date of invitation to bid shall govern, unless otherwise specified. Standards marked with an asterisk (*) are referenced only in the Notes, which are not requirements of this standard.
3.2 If there is a conflict between the requirements of any of the cited reference standards and this standard, the require-ments of this standard shall prevail.
3.3 SSPC STANDARDS:
SP 1 Solvent Cleaning* SP 2 Hand Tool Cleaning* SP 11 Power Tool Cleaning to Bare
Metal* SP 15 Commercial Grade Power Tool
Cleaning VIS 3 Guide and Reference Photographs
for Steel Surfaces Prepared by Hand and Power Tool Cleaning
3.4 INTERNATIONAL ORGANIZATION FOR STANDARD-IZATION (ISO):
* 8501-1 Preparation of steel substrates before application of paints and re-lated products: visual assessment of surface cleanliness, Part I
4. Surface Preparation Before and After Power Tool Cleaning
4.1 Before power tool cleaning, visible deposits of oil, grease, or other materials that may interfere with coating adhe-sion shall be removed in accordance with SSPC-SP 1 or other agreed-upon methods. Nonvisible surface contaminants such as soluble salts shall be treated to the extent specified by the procurement documents [project specifications] (see Note 8.2).
4.2 After power tool cleaning and prior to painting, reclean the surface if it does not conform to this standard.
4.3 After power tool cleaning and prior to painting, remove dirt, dust, or similar contaminants from the surface. Acceptable methods include brushing, blow off with clean, dry air, or vacuum cleaning.
5. Methods of Power Tool Cleaning
5.1 Use rotary or impact power tools to remove stratified rust (rust scale).
5.2 Use rotary or impact power tools to remove all weld slag.
5.3 Use power wire brushing, power abrading, power impact, or other power rotary tools to remove all loose mill scale, all loose or non-adherent rust, and all loose paint. Do not burnish the surface.
5.4 Operate power tools in a manner that prevents the formation of burrs, sharp ridges, and sharp cuts.
5.5 Regardless of the method used for cleaning, if specified in the procurement documents, feather the edges of remaining old paint so that the repainted surface can have a reasonably smooth appearance.
SSPC-SP 3November 1, 1982Editorial Revisions November 1, 2004
2-60
5.6 If approved by the owner, use blast cleaning as a substitute cleaning method for this standard.
6. Inspection
6.1 Unless otherwise specified in the procurement docu-ments, the contractor or material supplier is responsible for timely quality control to assure that the requirements of this document are met. Work and materials supplied under this standard are also subject to inspection by the purchaser or an authorized representative. Materials and work areas shall be accessible to the inspector.
6.2 Conditions not complying with this standard shall be corrected. In the case of a dispute, an arbitration or settlement procedure established in the procurement documents (project specification) shall be followed. If no arbitration or settlement procedure is established, then a procedure mutually agree-able to purchaser and material supplier (or contractor) shall be used.
7. Disclaimer
7.1 While every precaution is taken to ensure that all in-formation furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, coatings, or methods specified herein, or of the specification or standard itself.
7.2 This standard does not attempt to address problems concerning safety associated with its use. The user of this stan-dard, as well as the user of all products or practices described
herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.
8. Notes
Notes are not requirements of this standard.
8.1 Note that the use of visual standards in conjunction with this standard is required only when they are specified in the procurement documents (project specification) covering the work. It is recommended, however, that the use of visual stan-dards be made mandatory in the procurement documents. SSPC-VIS 3 provides a suitable comparative visual stan-dard for SSPC-SP 2, SSPC-SP 3, SSPC-SP 11, and SSPC-SP 15. ISO 8501-1 may also serve as a visual standard.
8.2 The Surface Preparation Commentary, SSPC-SP COM, contains additional information and data relevant to this specification. The Commentary is non-mandatory and is not a part of this specification. The table below lists the subjects discussed relevant to power tool cleaning and the appropriate Commentary Section.
Subject Commentary Section Film Thickness ............................................... 10 Rust Back ...................................................... 4.5 Rust, Stratified Rust, Pack Rust, and Rust Scale ................................. 4.3.1 Visual Standards ............................................ 11 Weld Spatter ............................................... 4.4.1
1
SSPC-SP WJ-1/NACE WJ-1March 10, 2012
This SSPC: The Society for Protective Coatings/NACE International joint surface preparation standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard practice. Nothing contained in this SSPC/NACE standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by letters patent, or as indemnifying or protecting anyone against liability for infringement of letters patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. SSPC and NACE assume no responsibility for the interpretation or use of this standard by other parties, and accept responsibility for only those offi-cial SSPC or NACE interpretations issued by SSPC or NACE in accordance with their governing procedures and policies, which preclude the issuance of interpretations by individual volunteers.
Users of this SSPC/NACE standard are responsible for reviewing appropriate health, safety, and regulatory docu-ments and for determining their applicability in relation to this standard prior to its use. This SSPC/NACE standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this SSPC/NACE standard also are responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appro-priate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard.
CAUTIONARY NOTICE: SSPC/NACE joint surface prep-aration standards are subject to periodic review, and may be revised or withdrawn at any time in accordance with SSPC/NACE technical committee procedures. SSPC and NACE require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publi-cation and subsequently from the date of each reaffirmation or revision. The user is cautioned to obtain the latest edition. Purchasers of SSPC/NACE standards may receive current
information on all standards and other SSPC/NACE joint publications by contacting the organizations at the addresses below:
SSPC: The Society for Protective Coatings40 24th Street, 6th FloorPittsburgh PA 15222-4656+1 412-281-2331
NACE International1440 South Creek DriveHouston, TX 77084-4906+1 281-228-6200
Foreword
This SSPC/NACE joint standard defines the Clean to Bare Substrate (WJ-1) degree of surface cleanliness of coated or uncoated metallic substrates achieved by the use of waterjet cleaning prior to the application of a protective coating or lining. Waterjet cleaning is the use of pressurized surface prepara-tion water for removing coatings and other materials, including hazardous materials, from a substrate to achieve a defined degree of surface cleanliness. Waterjet cleaning includes various methods such as low-pressure water cleaning (LP WC), high-pressure water cleaning (HP WC), high-pressure waterjetting (HP WJ), and ultrahigh-pressure waterjetting (UHP WJ).
The four degrees of surface cleanliness achieved by waterjet cleaning, which are addressed in separate standards, are as follows:
Degree of Surface Cleanliness DesignationClean to Bare Substrate WJ-1Very Thorough Cleaning WJ-2
Thorough Cleaning WJ-3Light Cleaning WJ-4
Clean to Bare Substrate (WJ-1) provides a greater degree of surface cleanliness than Very Thorough Cleaning (WJ-2).
Waterjet cleaning to achieve the Clean to Bare Substrate (WJ-1) degree of surface cleanliness is used when the objec-tive is to remove every trace of rust and other corrosion products, coating, and mill scale. Discoloration of the surface may be present.
SSPC: The Society for Protective Coatings/NACE International
Joint Surface Preparation StandardWaterjet Cleaning of Metals
SSPC-SP WJ-1/NACE WJ-1 – Clean To Bare Substrate
SSPC- SP WJ-1/NACE WJ-1March 10, 2012
2
may be used in situations in which the degree of cleanliness is required, but protective coatings or linings are not immediately applied. (Paragraphs A1 and A2 of Appendix A provide addi-tional information.) Waterjet cleaning does not establish but may reveal an existing surface profile on a metallic substrate. If the existing surface profile is not acceptable for subsequent coating application, alternative surface preparation methods to create the required surface profile must be considered. (Para-graph A3 of Appendix A provides additional information.)
1.1.1 Clean to Bare Substrate (WJ-1) is the waterjet cleaning equivalent to the International Organization for Standardization (ISO)(1) 8501-12 degree of cleanliness Sa 3, cleaning to bare metal. ISO 8501-43 notes the use of various common terms for methods of waterjet cleaning: water jetting, water blast cleaning, hydrojetting, aquajetting, hydroblasting, aquablasting, and “cleaning by directing a jet of pressurized water onto the surface to be cleaned.”
1.1.2 Within the hierarchy of degrees of surface cleanli-ness achieved by waterjet cleaning, Clean to Bare Substrate (WJ-1) is intended to be similar to the degree of surface cleanliness of SSPC-SP 5/NACE No. 1,4 except that stains are permitted to remain on the surface.
1.2 Although carbon steel is the metallic substrate most frequently cleaned in the field using waterjetting technology, waterjet cleaning may be used on metallic substrates other than carbon steel, including other ferrous substrates such as alloy steels, stainless steels, ductile iron and cast irons, nonferrous substrates such as aluminum, and copper alloys such as bronze. For convenience, the written definitions of the degrees of surface cleanliness of the metallic substrate use the general term “rust and other corrosion products.” The term “rust” is intended to apply to carbon steel substrates and the term “other corrosion products” (such as surface oxides) is intended to apply to metallic substrates other than carbon steel that are being waterjet cleaned. “Flash rust” is an oxidation product that forms as a wetted carbon steel substrate dries. The visual guides and comparators referenced for cleanliness and flash rust only illustrate carbon steel substrates.
1.3 This standard does not address surface preparation of concrete. Information on surface preparation of concrete can be found in SSPC-SP 13/ NACE No. 6.5
1.4 This standard is limited to requirements for visible surface contaminants. Information on nonvisible contamina-tion can be found in Paragraph A8 of Appendix A.
Section 2: Definitions
2.1 Clean to Bare Substrate (WJ-1): A metal surface after Clean to Bare Substrate, when viewed without magnifica-tion, shall have a matte (dull, mottled) finish and shall be free of all visible oil, grease, dirt, rust and other corrosion products, previous coatings, mill scale, and foreign matter.
(1) International Organization for Standardization (ISO), 1 ch. de la Voie-Creuse, Case postale 56, CH-1211 Geneva 20, Switzerland.
Waterjet cleaning does not provide the primary anchor pattern on the metallic substrate known as “surface profile.” The coatings industry uses waterjet cleaning primarily for recoating or relining projects in which there is an adequate pre-existing surface profile. The degrees of surface cleanli-ness cited above to be achieved by waterjet cleaning methods are not intended to require that a surface profile be present or defined prior to coating application.
Waterjet cleaning reduces and may completely remove water-soluble surface contaminants, notably those contami-nants found at the bottom of pits on the surface of corroded metallic substrates. Waterjet cleaning also helps remove oil, grease, rust and other corrosion products, and other foreign matter (for example, shotcrete spatter) from the surface, and is used when it is a more feasible method of surface preparation than, for example, abrasive blast cleaning, power or hand tool cleaning, or chemical stripping. Waterjet cleaning may be used when the application of high-performance coatings requires extensive surface preparation, surface decontamination, or both.
This standard is intended for use by coating or lining specifiers, applicators, inspectors, or others who have respon-sibility to define a standard degree of surface cleanliness to be achieved by waterjet cleaning methods.
This standard was prepared by SSPC/NACE Joint Task Group (TG) 275, “Surface Preparation of Metals to WJ-1 (Clean to Bare Substrate) by High-Pressure Waterjetting.” TG 275 is administered by Specific Technology Group (STG) 04, “Coatings and Linings, Protective—Surface Preparation,” and is sponsored by STG 02, “Coatings and Linings, Protec-tive—Atmospheric,” and STG 03, “Coatings and Linings, Protective—Immersion and Buried Service.” This standard is issued by SSPC Group Committee C.2 on Surface Preparation, and by NACE under the auspices of STG 04. This standard is one of a set of four standards on degrees of surface clean-liness to be achieved by waterjet cleaning that are intended to replace SSPC-SP 12/NACE No. 5,1 which includes all four degrees of surface cleanliness.
In SSPC/NACE standards, the terms shall, must, should, and may are used in accordance with Paragraph 2.2.1.8 of the Agreement between SSPC: The Society for Protective Coatings and NACE International. The terms shall and must are used to state mandatory requirements. The term should is used to state something considered good and is recom-mended, but is not mandatory. The term may is used to state something considered optional.
Section 1: General
1.1 This standard defines the Clean to Bare Substrate (WJ-1) degree of surface cleanliness of uncoated or coated metallic substrates by use of waterjet cleaning. The defined degree of cleanliness shall be achieved prior to the application of a specified protective coating or lining system. These require-ments include the end condition of the surface and materials and procedures necessary to achieve and verify the end condi-tion, as determined by visual inspection. This standard also
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2.1.1 Thin films of mill scale, rust and other corrosion products, and coating are not allowed. (Paragraphs A4 and A5 provide additional information).
2.1.2 The gray to brown-black discoloration remaining on corroded and pitted carbon steel that cannot be removed by further waterjet cleaning is allowed.
2.1.3 SSPC-VIS 4/NACE VIS 76 or other visual guide or
comparator may be specified to supplement the written defini-tion. In any dispute, the written standard shall take precedence over the visual guide or comparator. (Paragraph A6 of Appendix A provides additional information.)
Section 3: Additional Technical Considerations
3.1 Flash Rust
Flash rust is an additional consideration when a carbon steel substrate is subjected to waterjet cleaning. Gray or brown-black discoloration remaining in the pits of waterjet cleaned carbon steel is not the same as flash rust. Metals other than carbon steel can manifest discoloration as well. Degrees of flash rust may be qualitatively described as follows:
3.1.1 No flash rust: A carbon steel surface that, when viewed without magnification, exhibits no visible flash rust.
3.1.2 Light (L) flash rusted surface: A carbon steel surface that, when viewed without magnification, exhibits small quantities of a rust layer through which the carbon steel substrate may be observed. The rust or discoloration may be evenly distributed or present in patches, but it is tightly adherent and not easily removed by lightly wiping with a cloth.
3.1.3 Moderate (M) flash rusted surface: A carbon steel surface that, when viewed without magnification, exhibits a layer of rust that obscures the original carbon steel surface. The rust layer may be evenly distributed or present in patches, but it is reasonably well adherent and leaves light marks on a cloth that is lightly wiped over the surface.
3.1.4 Heavy (H) flash rusted surface: A carbon steel surface that, when viewed without magnification, exhibits a layer of heavy rust that hides original carbon steel surface completely. The rust may be evenly distributed or present in patches, but it is loosely adherent, easily comes off, and leaves significant marks on a cloth that is lightly wiped over the surface.
(Paragraphs A6, A9, and A10 of Appendix A provide addi-tional information. Appendix B provides additional information on methods of assessing the degree of flash rust.)
3.2 Appearance Variations
3.2.1 Acceptable variations in appearance that do not affect the degree of surface cleanliness defined in Paragraph
2.1 include variations caused by composition of the metallic substrate, original surface condition, thickness of the metal, weld metal, mill or fabrication marks, heat treating, heat-affected zones, and differences resulting from the initial abrasive blast cleaning abrasives or the abrasive blast pattern if previously blast cleaned, or waterjet cleaning pattern.
3.2.1.1 Carbon steel surfaces cleaned by waterjet cleaning initially exhibit a matte finish with a color that can range from light gray to dark brown-black but immediately acquires a golden hue unless a corrosion inhibitor or environmental controls are used. The matte finish on older carbon steel surfaces that have areas from which coating was removed and areas that were coating-free at the time of cleaning varies even when all visible surface material has been removed.
3.2.2 Metallic substrates show variations in texture, shade, color, tone, pitting, flaking, and mill scale that should be considered during the waterjet cleaning process. (Paragraph A6 of Appendix A provides additional information.)
3.2.3 Direct correlation to existing dry abrasive blasting standards and visual comparators is inaccurate or inappropriate.
Section 4: Associated Documents
4.1 Documents associated with this standard and cited in its mandatory sections include:
Document Title
SSPC-SP 5/NACE No. 1 “White Metal Blast Cleaning”SSPC-SP 13/NACE No. 6 “Surface Preparation
of Concrete”SSPC-VIS 4/NACE VIS 7 “Guide and Visual Reference
Photographs for Steel Cleaned by Waterjetting”
SSPC-SP 17 “Solvent Cleaning”
4.2 If there is a conflict between the requirements of any of the documents listed in Paragraph 4.1 and this standard, the requirements of this standard shall govern.
Section 5: Procedures Before Waterjet Cleaning
5.1 Precleaning: Visible deposits of oil, grease, foreign matter, and other contaminants shall be removed by waterjet cleaning, by methods in accordance with SSPC-SP 1, or as specified. (Paragraphs A4, A5, and A10 of Appendix A and Paragraph C2.6 of Appendix C provide additional information.)
5.2 Prior to beginning waterjet cleaning, surface imper-fections such as sharp fins, sharp edges, weld spatter, or burning slag shall be addressed to the extent required by the procurement documents (project specifications). (Paragraph A12 of Appendix A provides additional information.)
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5.3 CAUTION: Waterjet cleaning can be destructive to nonmetallic surfaces. Wood, rubber, insulation, electric instal-lations, instrumentation, etc., must be protected from direct and indirect impingement of water streams.
5.4 If a visual guide or comparator is specified to supple-ment the written standard, the condition of the substrate prior to waterjet cleaning should be determined before the waterjet cleaning commences. (Paragraph A6 of Appendix A provides additional information.)
Section 6: Waterjet Cleaning Methods
6.1 Any of the following waterjet cleaning methods may be used to achieve the Clean to Bare Substrate (WJ-1) degree of surface cleanliness. These waterjet cleaning methods all require the use of surface preparation water (hereinafter referred to as “SP water”) in accordance with Paragraph 6.2. The presence of toxic metals in a coating being removed can place restrictions on the methods of cleaning permitted. The chosen method shall comply with applicable regulations. (Para-graph A13 of Appendix A and Paragraph C2.3 of Appendix C provide additional information.)
6.1.1 Water cleaning (WC): Use of pressurized SP water discharged from a nozzle to remove unwanted matter from a surface.
6.1.1.1 Low-pressure water cleaning (LP WC): Water cleaning performed at pressures less than 34 MPa (5,000 psig). This is also called “power washing” or “pressure washing.”
6.1.1.2 High-pressure water cleaning (HP WC): Water cleaning performed at pressures from 34 to 70 MPa (5,000 to 10,000 psig).
6.1.2 Waterjetting (WJ): Use of SP water discharged from a nozzle at pressures of 70 MPa (10,000 psig) or greater to prepare a surface for coating or inspection. The velocity of the SP water exiting the orifice is greater than 340 m/s (1,100 ft/s).
6.1.2.1 High-pressure waterjetting (HP WJ): Waterjet-ting performed at pressures from 70 to 210 MPa (10,000 to 30,000 psig).
6.1.2.2 Ultrahigh-pressure waterjetting (UHP WJ): Waterjetting performed at pressures greater than 210 MPa (30,000 psig).
6.2 Surface preparation water (SP water): Water of sufficient purity and quality that it does not prevent the surface being cleaned from achieving the WJ-1 degree of surface cleanliness or nonvisible contamination criteria when contained in the procurement documents. SP water should not contain sediments or other impurities that are destructive to the proper functioning of the cleaning equipment. (Paragraph A7 of Appendix A provides additional information.)
Section 7: Procedures Following Waterjet Cleaning and Immediately Prior to Coating
7.1 Visible deposits of oil, grease, foreign matter, and other contaminants shall be removed by waterjet cleaning, by methods in accordance with SSPC-SP 1, or as specified. (Paragraphs A4, A5, A10, and A11 of Appendix A and Para-graph C2.6 of Appendix C provide additional information.)
7.2 The existing surface profile shall be assessed to determine conformance with the requirements of the procure-ment documents. (Paragraphs A3 and A14 of Appendix A provide additional information.)
7.3 Immediately prior to coating application, the entire surface shall comply with the degree of surface cleanliness specified herein, and to the extent established, the procure-ment document (project specification) requirements, and degree of flash rust.
7.4 Flash rust shall be mitigated in accordance with the requirements of the procurement documents. An example of a specification statement is provided in Paragraph A10 of Appendix A. It is common practice to remove heavy flash rust by LP WC, HP WC, or dry abrasive sweep blasting.
7.5 Dust and loose residues shall be removed from cleaned surfaces by brushing; blowing off with clean, dry air; vacuum cleaning; or other specified methods. Moisture separators, oil separators, traps, or other equipment may be necessary to achieve clean, dry air. (Paragraph A13 of Appendix A provides additional information.)
References
1. SSPC-SP 12/NACE No. 5 (latest revision), “Surface Prep-aration and Cleaning of Metals by Waterjetting Prior to Recoating” (Pittsburgh, PA: SSPC, and Houston, TX: NACE).
2. ISO 8501-1 (latest revision), “Preparation of steel substrates before application of paints and related prod-ucts—Visual assessment of surface cleanliness—Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings” (Geneva, Switzerland: ISO).
3. ISO 8501-4 (latest revision), “Preparation of steel substrates before application of paints and related prod-ucts—Visual assessment of surface cleanliness—Part 4: “Initial surface conditions, preparation grades and flash rust grades in connection with high-pressure water jetting” (Geneva, Switzerland: ISO).
4. SSPC-SP 5/NACE No. 1 (latest revision), “White Metal Blast Cleaning” (Pittsburgh, PA: SSPC, and Houston, TX: NACE).
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5. SSPC-SP 13/NACE No. 6 (latest revision), “Surface Prep-aration of Concrete” (Pittsburgh, PA: SSPC, and Houston, TX: NACE).
6. SSPC-VIS 4/NACE VIS 7 (latest revision), “Guide and Visual Reference Photographs for Steel Cleaned by Waterjetting” (Pittsburgh, PA: SSPC, and Houston, TX: NPA Guide ACE).
7. SSPC-SP 1 (latest revision), “Solvent Cleaning” (Pitts-burgh, PA: SSPC).
8. SSPC-PA Guide 4 (latest revision), “Guide to Maintenance Repainting with Oil Base or Alkyd Painting Systems” (Pittsburgh, PA: SSPC).
9. SSPC-Guide 15 (latest revision), “Field Methods for Retrieval and Analysis of Soluble Salts on Steel and Other Nonporous Substrates” (Pittsburgh, PA: SSPC).
10. SSPC-SP COM (latest revision), “Surface Preparation Commentary for Steel and Concrete Substrates” (Pitts-burgh, PA: SSPC).
11. NACE SP0178 (formerly RP0178) (latest revision), “Design, Fabrication, and Surface Finish Practices for Tanks and Vessels to Be Lined for Immersion Service” (Houston, TX: NACE).
12. SSPC-PA 2 (latest revision), “Measurement of Dry Coating Thickness with Magnetic Gages” (Pittsburgh, PA: SSPC).
13. “Recommended Guidelines for Evaluating Flash Rust” (Charleston, SC: National Shipbuilding Research Program [NSRP],(2) 2009). (Available from SSPC and NACE.)
14. ISO 8502-3 (latest revision), “Preparation of steel substrates before application of paints and related products—Tests for the assessment of surface clean-liness––Part 3: Assessment of dust on steel surfaces prepared for painting (pressure-sensitive tape method)” (Geneva, Switzerland: ISO).
15. ASTM(3) D 3359 (latest revision), “Standard Test Methods for Measuring Adhesion by Tape Test” (West Conshohocken, PA: ASTM).
16. “Recommended Practices for the Use of Manually Oper-ated High-Pressure Waterjetting Equipment” (latest revision) (St. Louis, MO: WaterJet Technology Associa-tion [WJTA]).(4)
17. D.A. Summers, WaterJetting Technology (London, UK: Chapman and Hall, 1995).
(2) National Shipbuilding Research Program (NSRP), Advanced Technology International (ATI), 5300 International Blvd., Charleston, SC 29418-6937.
(3) ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.(4) WaterJet Technology Association (WJTA), 906 Olive St., Suite 1200, St. Louis, MO
63101-1448.
18. SSPC-Guide 6 (latest revision), “Guide for Containing Debris Generated During Paint Removal Operations” (Pittsburgh, PA: SSPC).
Appendix A: Explanatory Notes(Nonmandatory)
This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this stan-dard is not required to follow, but may choose to follow, any or all of the the provisions herein.
A1 Function: Clean to Bare Substrate (WJ-1) provides a greater degree of surface cleanliness than Very Thorough Cleaning (WJ-2). The hierarchy of waterjet cleaning standards is as follows: WJ-1, WJ-2, WJ-3, and WJ-4. Clean to Bare Substrate (WJ-1) should be used when the highest degree of cleaning is required. The primary functions of waterjet cleaning before coating are:
(a) To remove material from the surface that can cause early failure of the coating system;
(b) To enhance the adhesion of the new coating system; (c) To expose the surface profile of the substrate that
is underneath the existing coating or rust and other corrosion products. (Paragraph A3 provides addi-tional information.); and
(d) To reduce or remove nonvisible contamination.
Clean to Bare Substrate (WJ-1) is used when the objective is to remove every trace of the coating, mill scale, and rust and other corrosion products, and when the extra effort required to remove all of these materials is determined to be warranted. Discoloration of the metal substrate surface may be present. Waterjet cleaning reduces and may completely remove water-soluble surface contaminants, notably those contaminants found at the bottom of pits on the surface of corroded metallic substrates.
A2 Maintenance Coating Work: When this standard is used in maintenance coating work, specific instructions should be provided on the extent of surface to be waterjet cleaned or spot-waterjet cleaned to this degree of surface cleanliness. In these cases, the surface cleanliness should be achieved across the entire area specified. For example, if all weld seams are to be cleaned in a maintenance operation, the degree of surface cleanliness applies to 100 percent of all weld seams. If the entire structure is to be cleaned, this degree of surface cleanliness applies to 100 percent of the entire structure. SSPC-PA Guide 48 provides a description of accepted practices for retaining old sound coating, removing unsound coating, feathering, and spot cleaning.
A3 Surface Profile: Waterjet cleaning reveals the surface profile (roughness) of the substrate that exists under the original coatings or rust and other corrosion products. When a coating is specified, another surface preparation method may
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be needed in addition to the waterjet cleaning to achieve the surface profile suitable for the specified coating system.
A4 Rust Scale: If rust scale is present, it must be removed. Rust scale is not a suitable substrate over which to apply coatings, and, if not removed, may also prevent removal of water-soluble salts that may accelerate corrosion. Methods other than waterjet cleaning may be used.
A5 Mill Scale: Mill scale is not allowed in this degree of surface cleanliness. Mill scale is that dark blue-black layer of iron oxide on the surface of hot-rolled steel. Over time, the adherence of the mill scale can change. Older mill scale might be removed easily in the field with waterjetting at 100 MPa (15,000 psi) and above. Waterjetting at pressures greater than 240 MPa (35,000 psig) is capable of removing tightly adherent mill scale, but production rates are not always cost effective. When the mill scale comes off, the steel surface under the mill scale has whatever surface profile is under the mill scale.
A6 Reference Photographs: Photographs may be speci-fied to supplement the written definition. SSPC VIS 4/NACE VIS 7 depicts various precleaning conditions and the appear-ance of a carbon steel surface that is consistent with the Clean to Bare Substrate (WJ-1) degree of surface cleanliness defined in this standard. In any dispute, the written standard shall take precedence over the visual guide. The visual appearance of carbon steel that has heavily flash rusted after initial waterjet cleaning and is then recleaned by LP WC has a different appearance from the original light flash-rusted steel depicted in SSPC VIS 4/NACE VIS 7.
A7 Quality of Water: SP water used by waterjet cleaning equipment should be clean and free of erosive silts or other contaminants that damage pump valves and/or prevent the surface from achieving the specified degree of surface cleanli-ness. A general rule is that the cleaner the water, the longer the service life of the waterjet cleaning equipment. The use of deionized water may be detrimental to some water pumps and care should be taken to ensure compatibility.
A8 Nonvisible Contamination (NV)
A8.1 Nonvisible contamination (NV): Nonvisible contamination is the presence of organic matter, such as thin films of oil and grease, and inorganic and/or soluble ionic materials such as chlorides, ferrous salts, nitrates, and sulfates that may be present on the substrate. (Paragraphs A6, A7, and A8 provide additional information.)
A8.2 Steel contaminated with water-soluble salts (e.g., sodium chloride and potassium sulfate) rapidly develops rust-back. Rust-back can be minimized by removing these salts from the steel surface and eliminating sources of recontami-nation during and after cleaning. These contaminants, along with their concentrations, may be identified using laboratory and field tests as described in SSPC Guide 15.9 Conductivity measurement is another method for testing for water-soluble salts.
A8.3 Other nonvisible contaminants (e.g., oil, acid, base, silicone, wax) may have an effect on coating performance. Coatings manufacturers should be consulted for recommenda-tions of maximum surface contamination allowed. The specifier should determine what level of nonvisible contaminants may remain.
A8.4 The test method or procedure to be used for determining the level of remaining nonvisible contaminants should be addressed in the procurement documents (project specification).
A8.5 The level of nonvisible contaminants found in an extraction from the surface that may remain on the surface is usually expressed as mass per unit area; for example, µg/cm2 or mg/m2 (1 µg/cm2 = 10 mg/m2).
A8.6 The following is an example specification for salt contamination based on concentration measurements:
“Immediately prior to the application of the coating, the surface extract shall not contain more than xx µg/cm2 of the specific contaminant (e.g., chloride) when tested with a speci-fied method.”
A8.7 The following is an example specification for salt contamination based on conductivity measurements:
“Immediately prior to the application of the coating, the conductivity of the surface extract shall not exceed xx µS/cm when tested with a specified method.”
A9 Use of Corrosion Inhibitors: It may be advantageous to add corrosion inhibitors to the SP water or apply them to the surface immediately after waterjet cleaning to temporarily prevent rust formation. Some corrosion inhibitor treatments may interfere with the performance of certain coatings systems. The coatings manufacturer should be consulted to ensure the compatibility of corrosion inhibitors with the coatings.
A10 Specification Statement:
A10.1 The specifier should use the degree of surface cleanliness and one of the degrees of flash rust to specify the required end condition. The following are examples of a speci-fication statement:
“All surfaces to be recoated shall be waterjet cleaned to SSPC-SP WJ-1 L/NACE WJ-1/L, Clean to Bare Substrate, Light Flash Rust.”
“At the time of the recoating, the degree of flash rust shall be no greater than moderate (M).”
A10.2 In addition, the specifier should consider whether a surface should be cleaned as required to achieve a particular, not to exceed maximum, level of nonvisible contamination (NV) prior to recoating. A suggested specification statement for nonvisible contamination (NV) is given in Paragraph A8.
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A11 Flash Rust: An oxidation product that forms as a wetted carbon steel substrate dries. With the exception of stainless steel surfaces, any steel surface may show flash rust within 30 minutes or longer while the substrate is drying (water evaporation) after waterjet cleaning, depending on environmental conditions. Flash rust has the appearance of rust bloom. Flash rust quickly changes the appearance of the waterjet cleaned surface and may be reduced or eliminated by physical or chemical methods. The color of the flash rust may vary depending on the age and composition of the steel and the time-of-wetness of the substrate prior to drying. With time, the flash rust changes from a yellow-brown, well adherent, light rust to a red-brown, loosely adherent, heavy rust. Appendix B contains additional information on methods of assessing the degree of flash rust.
A12 Surface Imperfections:
A12.1 Surface imperfections that can cause premature failure are often present. Coatings tend to pull away from sharp edges and projections, leaving little or no coating to protect the underlying steel. Other features that are difficult to prop-erly cover and protect include crevices, weld porosities, and laminations.
A12.2 Poorly adhering fabrication defects, such as weld slag residues, loose weld spatter, and surface laminations may be removed during the waterjet cleaning operation. Other surface defects, such as steel laminations, weld porosities, or deep corrosion pits may not be evident until the surface prepa-ration has been completed. Therefore, proper planning for such surface repair work should be given prior consideration because the timing of the repairs may occur before, during, or after the waterjet cleaning operation. The SSPC-SP COM10
and NACE SP017811 contain additional information on surface imperfections.
A12.3 The high cost of the methods to remedy surface imperfections (e.g., edge rounding and weld spatter removal) should be compared with the benefits of preventing premature coating failure. Therefore, those responsible for establishing the requirements and those responsible for performing the work should agree on the procedures to be used to repair surface imperfections to the extent required in the procurement documents (project specification).
A13 Removal of Coatings with Hazardous Compo-nents—Hygiene: Waterjet cleaning is often used to remove coatings with hazardous components. Because the particles are wetted, respiratory protection requirements for waterjet cleaning may be less stringent than for other methods of surface preparation. However, the wetted particles tend to stay on the skin. Applicable industrial hygiene tests should be performed to determine the destination of the wetted particles. Good industrial hygiene should be followed.
A14 Film Thickness: It is essential that ample coating be applied after waterjet cleaning to adequately cover the
peaks of the surface profile. The dry film thickness of the coating above the peaks of the surface profile should equal the thickness known to be needed for the desired protection. If the dry film thickness over the peaks is inadequate, prema-ture rust-through or coating failure will occur. To ensure that coating thicknesses are properly measured, the procedures in SSPC-PA 212 for verification of accuracy of Type 1 and Type 2 gauges should be used.
Appendix BMethods of Assessing the Degree of Flash Rust(Nonmandatory)
This appendix is considered nonmandatory, although it
may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this stan-dard is not required to follow, but may choose to follow, any or all of the the provisions herein.
The degree of flash rust is related to the quantity of loose, clean rust dust that is present on the surface. One of the following alternative methods may be used to assess the degree of flash rust, or other methods may be used if specified.
B1 Wipe Test
The following procedure is suggested to standardize the amount of pressure used to perform a wipe test on a flash-rusted surface:
(a) Neatly wrap a white, lint-free, woven cloth around a standard 100 mm (4 in) nylon paint brush, and hold it in place in a manner that prevents the cloth from slipping.
(b) Swipe the cloth-wrapped paint brush across the flash-rusted surface in one motion, using pressure equivalent to that used to apply house paint to a door. The length of the swipe should be consistent (e.g., one pass covering 1,500 mm [6 in] in length).
(c) Remove the white cloth from the paint brush and evaluate the color and amount of rust on the cloth. “Recommended Guidelines for Evaluating Flash Rust,”13 issued by the NSRP, provides guidance to perform this evaluation of flash rust.
If lint deposition is a concern, the project specification may require use of an alternate technique to determine the degree of flash rust.
B2 Tape Pull Test
The tape pull test is a modification of the pressure-sensi-tive tape method in ISO 8502-3.14 The procedure is as follows:
(a) Select a test area on the flash-rusted surface to perform the test.
(b) Place a 50 mm (2 in) long piece of tape (as specified in ASTM D 335915) on the selected test area and rub it thoroughly with a fingertip (not a fingernail) to ensure that the tape adheres firmly. Then peel the tape off
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the surface and place it on a piece of white paper for reference.
(c) Repeat the procedure in (b) nine times (for a total of 10 times) using a fresh piece of tape applied to the same spot on the surface (selected test area) each time.
(d) Assess the appearance of the 10th tape and the appearance of the test area on the flash-rusted surface after the 10th tape is pulled off in accordance with Table B1.
Appendix C: Waterjet Cleaning Equipment and Operating Parameters (Nonmandatory)
This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this stan-dard is not required to follow, but may choose to follow, any or all of the the provisions herein.
C1 Waterjet Cleaning Equipment
Multiple configurations of pumps, heads, and containment systems are suitable for waterjet cleaning operations. The equipment systems may include manual lances, fixed lances on platforms, or robot-driven systems. Additional descriptions relevant to waterjet cleaning systems are in the WaterJet Tech-nology Association’s “Recommended Practices for the Use of Manually Operated High-Pressure Waterjetting Equipment,”16 which also addresses concerns relevant to waterjet cleaning operations. The commercial waterjet cleaning unit can be mounted on a skid, trailer, or truck; can be equipped with various prime movers (diesel, electric motor, etc.); and usually consists of a pump, hoses, and various tools. The tools can be hand-held or mounted on a robot or controlled by a traversing mechanism. Water is propelled through a single jet, fan jet, pulse generator, or multiple rotating jets. Rotation of the nozzle head is provided by small electric, air, or hydraulic motors, or by slightly inclined orifices in a multiple-orifice nozzle.
C1.1 All waterjet cleaning units normally use a hydraulic hose with a minimum bursting strength of 2.5 times the capa-bility of its maximum-rated operating strength.
C1.2 Waterjet streams are produced by orifices, or tips, that can have different forms–the higher the pressure, the more limited is the choice of forms. Round jets are most commonly used, but orifices of other shapes are available. Tips can be designed to produce multiple jets of water that are normally rotated to achieve higher material-removal rates. Interchangeable nozzle tips should be used to produce the desired streams. The manufacturer should be consulted for specific recommendations.
C1.3 Effect of Corrosion Inhibitors and Detergents on Equipment: If corrosion inhibitors are to be used with the SP water, the manufacturer of the waterjet cleaning equipment should be consulted to ensure compatibility of corrosion inhibi-tors with the equipment. Compatibility of detergents with the special seals and high-alloy metals of the waterjet cleaning equipment should be carefully investigated to ensure that the cleaning equipment is not damaged.
C2 Operating Parameters
C2.1 Waterjet Cleaning Method Selection: The person performing the work should have sufficient experience to select the waterjet cleaning method and the specific combination of water pressure and flow (velocity and volume) to achieve the specified degree of surface cleanliness. A water flow rate of 4 to 53 L/min (1 to 14 gal/min) is typical.
(a) LP WC or HP WC (the flow rate of the water is the dominant energy characteristic);
(b HP WJ (pressure or water velocity and flow rate are equally important); or
(c) UHP WJ (pressure or water velocity is the dominant energy characteristic).
C2.2 Stand-off Distance: The distance from the nozzle to the work piece surface (stand-off distance) is critical for effec-tive cleaning with any of the waterjet cleaning methods. Typical stand-off distances for HP WJ and UHP WJ range from 25 to 150 mm (1.0 to 6.0 in) for coatings removal. Typical stand-off distances range up to 600 mm (24 in) to remove foreign matter that is not tightly adherent. Excessive stand-off distance does not produce the desired cleaning.
TABLE B1ASSESSMENT OF DEGREE OF FLASH RUST—TAPE PULL TEST
Degree of Flash Rust Appearance of 10th Tape(after final pull from test area)
Appearance of Test Area (after 10th tape pull)
Light No rust on tape No change, or only slight change in test area appearance
Moderate Slight, localized red-brown rust on tape Significant change of test area appearance, showing localized areas of black rust
Heavy Significant, uniform red-brown rust on tape, also showing grains of black rust
Significant change of test area appearance, showing localized areas of black rust
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SSPC-SP WJ-1/NACE WJ-1March 10, 2012
C2.3 Threshold Pressure: The threshold pressure of a coating can be determined. In general, the tougher, more resil-ient, or harder the coating (i.e., the more resistant to probing or cutting by a pocket knife), the higher the threshold pressure; the softer and more jelly-like the coating, the lower the threshold pressure. Threshold pressure is defined by Summers17 as the minimum required pressure to penetrate the material. Once the threshold pressure is achieved or exceeded, the produc-tion rate increases dramatically. Therefore, waterjet cleaning production rates can be classified according to two conditions:
(a) Relatively Slow—Erosion at pressures lower than the threshold pressure; and
(b) Relatively Fast—Waterjet cutting and erosion at pres-sures greater than the threshold pressure.
Pressure loss is a function of the flow rate of the water through the hose and the inside diameter of the hose. The manufacturer should be consulted for specific information on potential pressure loss for each type of equipment.
C2.4 Depending on the initial condition of the area and the materials to be removed, the choice of waterjet cleaning method to achieve Clean to Bare Substrate (WJ-1) is ulti-mately based on the capabilities of the equipment and its components. Dwell time, traverse rate, pressure, flow, stand-off distances, the number of nozzles, and rotation speed all
interact in determining materials that remain and those that are removed.
C2.5 Reuse of Effluent Water: If effluent water is captured for reuse by the waterjet cleaning equipment, caution should be used to avoid introducing any removed contami-nants back onto the cleaned substrate. The effluent water may be placed in a clean holding tank and tested to determine the contaminant content prior to reintroduction into the water supply stream to the waterjet cleaning equipment. The effluent water should be monitored for suspended particulates, hydro-carbons, salts, hazardous materials, or other by-products of the surface preparation procedures.
C2.6 Additives: Any detergents, degreasers, or other types of cleaners used in conjunction with the waterjet cleaning method should be removed prior to applying a coating. If corro-sion inhibitors are to be used with the SP water, the coating manufacturer should be consulted to ensure compatibility of corrosion inhibitors with the coating.
C2.7 Containment Systems: Containment systems may consist of water-impermeable membranes or vacuum collec-tion heads or the systems described in SSPC-Guide 6.18 The containment design should consider the pressures used and water volumes produced and if the process may be open or closed loop (with a single pass or multiple passes of the water through the system)..
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This SSPC: The Society for Protective Coatings/NACE International joint surface preparation standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard practice. Nothing contained in this SSPC/NACE standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by letters patent, or as indemnifying or protecting anyone against liability for infringement of letters patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. SSPC and NACE assume no responsibility for the interpretation or use of this standard by other parties, and accept responsibility for only those offi-cial SSPC or NACE interpretations issued by SSPC or NACE in accordance with their governing procedures and policies, which preclude the issuance of interpretations by individual volunteers.
Users of this SSPC/NACE standard are responsible for reviewing appropriate health, safety, and regulatory docu-ments and for determining their applicability in relation to this standard prior to its use. This SSPC/NACE standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of mate-rials, equipment, and/or operations detailed or referred to within this standard. Users of this SSPC/NACE standard also are responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory require-ments prior to the use of this standard.
CAUTIONARY NOTICE: SSPC/NACE joint surface prep-aration standards are subject to periodic review, and may be revised or withdrawn at any time in accordance with SSPC/NACE technical committee procedures. SSPC and NACE require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publi-cation and subsequently from the date of each reaffirmation or revision. The user is cautioned to obtain the latest edition. Purchasers of SSPC/NACE standards may receive current
information on all standards and other SSPC/NACE joint publications by contacting the organizations at the addresses below:
SSPC: The Society for Protective Coatings40 24th Street, 6th FloorPittsburgh PA 15222-4656+1 412-281-2331
NACE International1440 South Creek DriveHouston, TX 77084-4906+1 281-228-6200
Foreword
This SSPC/NACE joint standard defines the Light Cleaning degree of surface cleanliness of coated or uncoated metallic substrates achieved by the use of waterjet cleaning prior to the application of a protective coating or lining. Waterjet cleaning is the use of pressurized surface preparation water for removing coatings and other materials, including hazardous materials, from a substrate to achieve a defined degree of surface clean-liness. Waterjet cleaning includes various methods such as low-pressure water cleaning (LP WC), high-pressure water cleaning (HP WC), high-pressure waterjetting (HP WJ), and ultrahigh-pressure waterjetting (UHP WJ).
The four degrees of surface cleanliness achieved by waterjet cleaning, which are addressed in separate standards, are as follows:
Degree of Surface Cleanliness Designation Clean to Bare Substrate WJ-1Very Thorough Cleaning WJ-2
Thorough Cleaning WJ-3Light Cleaning WJ-4
Light Cleaning (WJ-4) provides a a lesser degree of cleaning than Thorough Cleaning (WJ-3).
Waterjet cleaning to achieve the Light Cleaning (WJ-4) degree of surface cleanliness is used when the objective is to allow as much of the tightly adherent rust and other corro-sion products, coating, and mill scale to remain as possible, but when the extra effort required to remove more of these
SSPC: The Society for Protective Coatings/NACE InternationalJoint Surface Preparation Standard
Waterjet Cleaning of Metals SSPC-SP WJ-4/NACE WJ-4 – Light Cleaning
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materials is determined to be unwarranted. Discoloration of the surface may be present.
Waterjet cleaning does not provide the primary anchor pattern on the metallic substrate known as “surface profile.” The coatings industry uses waterjet cleaning primarily for recoating or relining projects in which there is an adequate pre-existing surface profile. The degrees of surface cleanli-ness cited above to be achieved by waterjet cleaning methods are not intended to require that a surface profile be present or defined prior to coating application.
Waterjet cleaning reduces and may completely remove water-soluble surface contaminants, notably those contami-nants found at the bottom of pits on the surface of corroded metallic substrates. Waterjet cleaning also helps remove oil, grease, rust and other corrosion products, and other foreign matter (for example, shotcrete spatter) from the surface, and is used when it is a more feasible method of surface preparation than, for example, abrasive blast cleaning, power or hand tool cleaning, or chemical stripping. Waterjet cleaning may be used when the application of high-performance coatings requires extensive surface preparation, surface decontamination, or both.
This standard is intended for use by coating or lining specifiers, applicators, inspectors, or others who have respon-sibility to define a standard degree of surface cleanliness to be achieved by waterjet cleaning methods.
This standard was prepared by SSPC/NACE Joint Task Group (TG) 278, “Surface Preparation of Metals to WJ-4 (Light Cleaning) by High-Pressure Waterjetting.” TG 278 is adminis-tered by Specific Technology Group (STG) 04, “Coatings and Linings, Protective—Surface Preparation,” and is sponsored by STG 02, “Coatings and Linings, Protective—Atmospheric,” and STG 03, “Coatings and Linings, Protective—Immersion and Buried Service.” This standard is issued by SSPC Group Committee C.2 on Surface Preparation, and by NACE under the auspices of STG 04. This standard is one of a set of four standards on degrees of surface cleanliness to be achieved by waterjet cleaning that are intended to replace SSPC-SP 12/NACE No. 5,1 which includes all four degrees of surface cleanliness.
In SSPC/NACE standards, the terms shall, must, should, and may are used in accordance with Paragraph 2.2.1.8 of the Agreement between SSPC: The Society for Protective Coatings and NACE International. The terms shall and must are used to state mandatory requirements. The term should is used to state something considered good and is recom-mended, but is not mandatory. The term may is used to state something considered optional.
Section 1: General
1.1 This standard defines the Light Cleaning (WJ-4) degree of surface cleanliness of uncoated or coated metallic substrates by use of waterjet cleaning. The defined degree of cleanliness shall be achieved prior to the application of a specified protective coating or lining system. These require-ments include the end condition of the surface and materials
and procedures necessary to achieve and verify the end condi-tion, as determined by visual inspection. This standard also may be used in situations in which the degree of cleanliness is required, but protective coatings or linings are not immediately applied. (Paragraphs A1 and A2 of Appendix A provide addi-tional information.) Waterjet cleaning does not establish but may reveal an existing surface profile on a metallic substrate. If the existing surface profile is not acceptable for subsequent coating application, alternative surface preparation methods to create the required surface profile must be considered. (Para-graph A3 of Appendix A provides additional information.)
1.1.1 Light Cleaning (WJ-4) is essentially equivalent to the International Organization for Standardization (ISO)(1) 8501-42
degree of cleanliness Wa 4, light cleaning. . ISO 8502-4 notes the use of various common terms for methods of waterjet cleaning: water jetting, water blast cleaning, hydrojetting, aqua-jetting, hydroblasting, aquablasting, and “cleaning by directing a jet of pressurized water onto the surface to be cleaned.”
1.1.2 Within the hierarchy of degrees of surface cleanli-ness achieved by waterjet cleaning, Light Cleaning (WJ-4)is intended to be similar to the degree of surface cleanliness of SSPC-SP 7/NACE No. 4,3 except that tightly adherent material, rather than only stains, is permitted to remain on the surface.
1.2 Although carbon steel is the metallic substrate most frequently cleaned in the field using waterjetting technology, waterjet cleaning may be used on metallic substrates other than carbon steel, including other ferrous substrates such as alloy steels, stainless steels, ductile iron and cast irons, nonferrous substrates such as aluminum, and copper alloys such as bronze. For convenience, the written definitions of the degrees of surface cleanliness of the metallic substrate use the general term “rust and other corrosion products.” The term “rust” is intended to apply to carbon steel substrates and the term “other corrosion products” (such as surface oxides) is intended to apply to metallic substrates other than carbon steel that are being waterjet cleaned. “Flash rust” is an oxidation product that forms as a wetted carbon steel substrate dries. The visual guides and comparators referenced for cleanliness and flash rust only illustrate carbon steel substrates.
1.3 This standard does not address surface preparation of concrete. Information on surface preparation of concrete can be found in SSPC-SP 13/NACE No. 6.4
1.4 This standard is limited to requirements for visible surface contaminants. Information on nonvisible contamina-tion can be found in Paragraph A8 of Appendix A.
Section 2: Definitions
2.1 Light Cleaning (WJ-4): A metal surface after Light Cleaning, when viewed without magnification, shall be free of all visible oil, grease, dirt, dust, loose mill scale, loose rust and other corrosion products, and loose coating. Any residual
1 International Organization for Standardization (ISO), 1 ch. de la Voie-Creuse, Case postale 56, CH-1211 Geneva 20, Switzerland.
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material shall be tightly adhered to the metal substrate and may consist of randomly dispersed stains of rust and other corro-sion products or previously applied coating, tightly adherent thin coatings, and other tightly adherent foreign matter.
2.1.1 Coatings, mill scale, and foreign matter are consid-ered tightly adherent if they cannot be removed by lifting with a dull putty knife. (Paragraphs A4 and A5 of Appendix A provide additional information.)
2.1.2 The gray to brown-black discoloration remaining on corroded and pitted carbon steel that cannot be removed by further waterjet cleaning is allowed.
2.1.3 SSPC-VIS 4/NACE VIS 75 or other visual guide or comparator may be specified to supplement the written defini-tion. In any dispute, the written standard shall take precedence over the visual guide or comparator. (Paragraph A6 of Appendix A provides additional information.)
Section 3: Additional Technical Considerations
3.1 Flash Rust
Flash rust is an additional consideration when a carbon steel substrate is subjected to waterjet cleaning. Gray or brown-black discoloration remaining in the pits of waterjet cleaned carbon steel is not the same as flash rust. Metals other than carbon steel can manifest discoloration as well. Degrees of flash rust may be qualitatively described as follows:
3.1.1 No flash rust: A carbon steel surface that, when viewed without magnification, exhibits no visible flash rust.
3.1.2 Light (L) flash rusted surface: A carbon steel surface that, when viewed without magnification, exhibits small quantities of a rust layer through which the carbon steel substrate may be observed. The rust or discoloration may be evenly distributed or present in patches, but it is tightly adherent and not easily removed by lightly wiping with a cloth.
3.1.3 Moderate (M) flash rusted surface: A carbon steel surface that, when viewed without magnification, exhibits a layer of rust that obscures the original carbon steel surface. The rust layer may be evenly distributed or present in patches, but it is reasonably well adherent and leaves light marks on a cloth that is lightly wiped over the surface.
3.1.4 Heavy (H) flash rusted surface: A carbon steel surface that, when viewed without magnification, exhibits a layer of heavy rust that hides original carbon steel surface completely. The rust may be evenly distributed or present in patches, but it is loosely adherent, easily comes off, and leaves significant marks on a cloth that is lightly wiped over the surface.
(Paragraphs A6, A9, and A10 of Appendix A provide addi-tional information. Appendix B provides additional information on methods of assessing the degree of flash rust.)
3.2 Appearance Variations
3.2.1 Acceptable variations in appearance that do not affect the degree of surface cleanliness defined in Paragraph 2.1 include variations caused by composition of the metallic substrate, original surface condition, thickness of the metal, weld metal, mill or fabrication marks, heat treating, heat-affected zones, and differences resulting from the initial abrasive blast cleaning abrasives or the abrasive blast pattern if previously blast cleaned, or waterjet cleaning pattern.
3.2.1.1 Carbon steel surfaces cleaned by waterjet cleaning initially exhibit a matte finish with a color that can range from light gray to dark brown-black but immediately acquires a golden hue unless a corrosion inhibitor or environmental controls are used. The matte finish on older carbon steel surfaces that have areas from which coating was removed and areas that were coating-free at the time of cleaning varies even when all visible surface material has been removed.
3.2.2 Metallic substrates show variations in texture, shade, color, tone, pitting, flaking, and mill scale that should be considered during the waterjet cleaning process. (Paragraph A6 of Appendix A provides additional information.)
3.2.3 Direct correlation to existing dry abrasive blasting standards and visual comparators is inaccurate or inappropriate.
Section 4: Associated Documents
4.1 Documents associated with this standard and cited in its mandatory sections include:
Document Title
SSPC-SP 7/NACE No. 4 “Brush-Off Blast Cleaning”
SSPC-SP 13/NACE No. 6 “Surface Preparation of Concrete”
SSPC-VIS 4/NACE VIS 7“Guide and Visual Reference Photographs for Steel Cleaned by Waterjetting”
SSPC-SP 16 “Solvent Cleaning”
4.2 If there is a conflict between the requirements of any of the documents listed in Paragraph 4.1 and this standard, the requirements of this standard shall govern.
Section 5: Procedures Before Waterjet Cleaning
5.1 Precleaning: Visible deposits of oil, grease, foreign matter, and other contaminants shall be removed by waterjet cleaning, by methods in accordance with SSPC-SP 1, or as specified. (Paragraphs A4, A5, and A10 of Appendix A and Paragraph C2.6 of Appendix C provide additional information.)
5.2 Prior to beginning waterjet cleaning, surface imper-fections such as sharp fins, sharp edges, weld spatter, or
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burning slag shall be addressed to the extent required by the procurement documents (project specifications). (Paragraph A12 of Appendix A provides additional information.)
5.3 CAUTION: Waterjet cleaning can be destructive to nonmetallic surfaces. Wood, rubber, insulation, electric instal-lations, instrumentation, etc., must be protected from direct and indirect impingement of water streams.
5.4 If a visual guide or comparator is specified to supple-ment the written standard, the condition of the substrate prior to waterjet cleaning should be determined before the waterjet cleaning commences. (Paragraph A6 of Appendix A provides additional information.)
Section 6: Waterjet Cleaning Methods
6.1 Any of the following waterjet cleaning methods may be used to achieve the Light Cleaning (WJ-4) degree of surface cleanliness. These waterjet cleaning methods all require the use of surface preparation water (hereinafter referred to as “SP water”) in accordance with Paragraph 6.2. The presence of toxic metals in a coating being removed can place restrictions on the methods of cleaning permitted. The chosen method shall comply with applicable regulations. (Paragraph A13 of Appendix A and Paragraph C2.3 of Appendix C provide addi-tional information.)
6.1.1 Water cleaning (WC): Use of pressurized SP water discharged from a nozzle to remove unwanted matter from a surface.
6.1.1.1 Low-pressure water cleaning (LP WC): Water cleaning performed at pressures less than 34 MPa (5,000 psig). This is also called “power washing” or “pressure washing.”
6.1.1.2 High-pressure water cleaning (HP WC): Water cleaning performed at pressures from 34 to 70 MPa (5,000 to 10,000 psig).
6.1.2 Waterjetting (WJ): Use of SP water discharged from a nozzle at pressures of 70 MPa (10,000 psig) or greater to prepare a surface for coating or inspection. The velocity of the SP water exiting the orifice is greater than 340 m/s (1,100 ft/s).
6.1.2.1 High-pressure waterjetting (HP WJ): Waterjet-ting performed at pressures from 70 to 210 MPa (10,000 to 30,000 psig).
6.1.2.2 Ultrahigh-pressure waterjetting (UHP WJ): Waterjetting performed at pressures greater than 210 MPa (30,000 psig).
6.2 Surface preparation water (SP water): Water of sufficient purity and quality that it does not prevent the surface being cleaned from achieving the WJ-4 degree of surface cleanliness or nonvisible contamination criteria when contained in the procurement documents. SP water should not
contain sediments or other impurities that are destructive to the proper functioning of the cleaning equipment. (Paragraph A7 of Appendix A provides additional information.)
Section 7: Procedures Following Waterjet Cleaning and Immediately Prior to Coating
7.1 Visible deposits of oil, grease, foreign matter, and other contaminants shall be removed by waterjet cleaning, by methods in accordance with SSPC-SP 1, or as specified. (Paragraphs A4, A5, A10, and A11 of Appendix A and Para-graph C2.6 of Appendix C provide additional information.)
7.2 The existing surface profile shall be assessed to determine conformance with the requirements of the procure-ment documents. (Paragraphs A3 and A14 of Appendix A provide additional information.)
7.3 Immediately prior to coating application, the entire surface shall comply with the degree of surface cleanliness specified herein, and to the extent established, the procure-ment document (project specification) requirements, and degree of flash rust.
7.4 Flash rust shall be mitigated in accordance with the requirements of the procurement documents. An example of a specification statement is provided in Paragraph A10 of Appendix A. It is common practice to remove heavy flash rust by LP WC, HP WC, or dry abrasive sweep blasting.
7.5 Dust and loose residues shall be removed from cleaned surfaces by brushing; blowing off with clean, dry air; vacuum cleaning; or other specified methods. Moisture separators, oil separators, traps, or other equipment may be necessary to achieve clean, dry air. (Paragraph A13 of Appendix A provides additional information.)
References
1. SSPC-SP 12/NACE No. 5 (latest revision), “Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating” (Pittsburgh, PA: SSPC and Houston, TX: NACE).
2. ISO 8501-4 (latest revision), “Preparation of steel substrates before application of paints and related prod-ucts—Visual assessment of surface cleanliness—Part 4: “Initial surface conditions, preparation grades and flash rust grades in connection with high-pressure water jetting” (Geneva, Switzerland: ISO).
3. SSPC-SP 7/NACE No. 4 (latest revision), “Industrial Blast Blast Cleaning” (Pittsburgh, PA: SSPC and Houston, TX: NACE).
4. SSPC-SP 13/ NACE No. 6 (latest revision), “Surface Prep-aration of Concrete” (Pittsburgh, PA: SSPC and Houston, TX: NACE).
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5. SSPC-VIS 4/NACE VIS 7 (latest revision), “Guide and Visual Reference Photographs for Steel Cleaned by Waterjetting” (Pittsburgh, PA: SSPC and Houston, TX: NACE).
6. SSPC-SP 1 (latest revision), “Solvent Cleaning” (Pitts-burgh, PA: SSPC).
7. SSPC-PA Guide 4 (latest revision), “Guide to Maintenance Repainting with Oil Base or Alkyd Painting Systems” (Pittsburgh, PA: SSPC).
8. SSPC-Guide 15 (latest revision), “Field Methods for Retrieval and Analysis of Soluble Salts on Steel and Other Nonporous Substrates” (Pittsburgh, PA: SSPC).
9. SSPC-SP COM (latest revision), “Surface Preparation Commentary for Steel and Concrete Substrates” (Pitts-burgh, PA: SSPC).
10. NACE SP0178 (formerly RP0178) (latest revision), “Design, Fabrication, and Surface Finish Practices for Tanks and Vessels to Be Lined for Immersion Service” (Houston, TX: NACE).
11. SSPC-PA 2 (latest revision), “Measurement of Dry Coating Thickness with Magnetic Gages” (Pittsburgh, PA: SSPC).
12. “Recommended Guidelines for Evaluating Flash Rust” (Charleston, SC: National Shipbuilding Research Program [NSRP],(2) 2009). (Available from SSPC and NACE.)
13. ISO 8502-3 (latest revision), “Preparation of steel
substrates before application of paints and related prod-ucts—Tests for the assessment of surface cleanliness – Part 3: Assessment of dust on steel surfaces prepared for painting (pressure-sensitive tape method)” (Geneva, Switzerland: ISO).
14. ASTM(3) D 3359 (latest revision), “Standard Test Methods for Measuring Adhesion by Tape Test” (West Conshohocken, PA: ASTM).
15. “Recommended Practices for the Use of Manually Oper-ated High-Pressure Waterjetting Equipment” (latest revision) (St. Louis, MO: WaterJet Technology Associa-tion [WJTA]).(4)
16. D.A. Summers, WaterJetting Technology (London, UK: Chapman and Hall, 1995).
17. SSPC-Guide 6 (latest revision), “Guide for Containing Debris Generated During Paint Removal Operations” (Pittsburgh, PA: SSPC).
(2) National Shipbuilding Research Program (NSRP), Advanced Technology International (ATI), 5300 International Blvd., Charleston, SC 29418-6937.
(3) ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959. (4) WaterJet Technology Association (WJTA), 906 Olive St., Suite 1200, St. Louis, MO
63101-1448.
Appendix A: Explanatory Notes(Nonmandatory)
This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this stan-dard is not required to follow, but may choose to follow, any or all of the the provisions herein.
A1 Function: Light Cleaning (WJ-4) provides a lesser degree of cleaning than Thorough Cleaning (WJ-3). The hier-archy of waterjet cleaning standards is as follows: WJ-1, WJ 2, WJ-3, and WJ-4. Light Cleaning (WJ-4) should be used when the service environment is mild enough to permit tight mill scale, coating, rust, and other foreign matter to remain on the surface. WJ-4 is typically used when a compatible coating is to be applied over existing coatings. The primary functions of waterjet cleaning before coating are:
(a) To remove material from the surface that can cause early failure of the coating system;
(b) To enhance the adhesion of the new coating system; (c) To expose the surface profile of the substrate that
is underneath the existing coating or rust and other corrosion products. (Paragraph A3 provides addi-tional information.); and
(d) To reduce or remove nonvisible contamination.
Light Cleaning (WJ-4) is used when the objective is to allow as much of the tightly adherent rust and other corrosion products, coating, and mill scale to remain as possible. Discol-oration of the metal substrate may be present. Discoloration of the metal substrate surface may be present. Waterjet cleaning reduces and may completely remove water-soluble surface contaminants, notably those contaminants found at the bottom of pits on the surface of corroded metallic substrates.
Light Cleaning (WJ-4) allows as much of the tightly adherent matter to remain as possible. Thorough Cleaning (WJ-3) allows staining or tightly adherent matter to a maximum of 33 percent of each unit area of the surface. Very Thorough Cleaning (WJ-2) allows staining or tightly adherent matter to a maximum of 5 percent of each unit area of the surface, and a Clean to Bare Substrate (WJ-1) surface is free of all visible rust and other corrosion products, dirt, previous coatings, mill scale, and foreign matter.
A2 Maintenance Coating Work: When this standard is used in maintenance coating work, specific instructions should be provided on the extent of surface to be waterjet cleaned or spot-waterjet cleaned to this degree of surface cleanliness. In these cases, the surface cleanliness should be achieved across the entire area specified. For example, if all weld seams are to be cleaned in a maintenance operation, the degree of surface cleanliness applies to 100 percent of all weld seams. If the entire structure is to be cleaned, this
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degree of surface cleanliness applies to 100 percent of the entire structure. SSPC-PA Guide 47 provides a description of accepted practices for retaining old sound coating, removing unsound coating, feathering, and spot cleaning.
A3 Surface Profile: Waterjet cleaning reveals the surface profile (roughness) of the substrate that exists under the original coatings or rust and other corrosion products. When a coating is specified, another surface preparation method may be needed in addition to the waterjet cleaning to achieve the surface profile suitable for the specified coating system.
A4 Rust Scale: If rust scale is present, it must be removed. Rust scale is not a suitable substrate over which to apply coatings, and, if not removed, may also prevent removal of water-soluble salts that may accelerate corrosion. Methods other than waterjet cleaning may be used.
A5 Mill Scale: Mill scale is not allowed in this degree of surface cleanliness. Mill scale is that dark blue-black layer of iron oxide on the surface of hot-rolled steel. Over time, the adherence of the mill scale can change. Older mill scale might be removed easily in the field with waterjetting at 100 MPa (15,000 psi) and above. Waterjetting at pressures greater than 240 MPa (35,000 psig) is capable of removing tightly adherent mill scale, but production rates are not always cost effective. When the mill scale comes off, the steel surface under the mill scale has whatever surface profile is under the mill scale.
A6 Reference Photographs: Photographs may be specified to supplement the written definition. SSPC-VIS 4/ NACE VIS 7 depicts various precleaning conditions and the appearance of a carbon steel surface that is consistent with the Light Cleaning (WJ-4) degree of surface cleanliness defined in this standard. In any dispute, the written standard shall take precedence over the visual guide. The visual appearance of carbon steel that has heavily flash rusted after initial waterjet cleaning and is then recleaned by LP WC has a different appearance from the original light flash-rusted steel depicted in SSPC-VIS 4/ NACE VIS 7.
A7 Quality of Water: SP water used by waterjet cleaning equipment should be clean and free of erosive silts or other contaminants that damage pump valves and/or prevent the surface from achieving the specified degree of surface cleanli-ness. A general rule is that the cleaner the water, the longer the service life of the waterjet cleaning equipment. The use of deionized water may be detrimental to some water pumps and care should be taken to ensure compatibility.
A8 Nonvisible Contamination (NV)
A8.1 Nonvisible contamination (NV): Nonvisible contamination is the presence of organic matter, such as thin films of oil and grease, and inorganic and/or soluble ionic mate-rials such as chlorides, ferrous salts, nitrates, and sulfates that may be present on the substrate. (Paragraphs A6, A7, and A8 provide additional information.)
A8.2 Steel contaminated with water-soluble salts (e.g., sodium chloride and potassium sulfate) rapidly develops rust-back. Rust-back can be minimized by removing these salts from the steel surface and eliminating sources of recontami-nation during and after cleaning. These contaminants, along with their concentrations, may be identified using laboratory and field tests as described in SSPC Guide 15.8 Conductivity measurement is another method for testing for water-soluble salts.
A8.3 Other nonvisible contaminants (e.g., oil, acid, base, silicone, wax) may have an effect on coating performance. Coatings manufacturers should be consulted for recommenda-tions of maximum surface contamination allowed. The specifier should determine what level of nonvisible contaminants may remain.
A8.4 The test method or procedure to be used for determining the level of remaining nonvisible contaminants should be addressed in the procurement documents (project specification).
A8.5 The level of nonvisible contaminants found in an extraction from the surface that may remain on the surface is usually expressed as mass per unit area; for example, µg/cm2 or mg/m2 (1 µg/cm2 = 10 mg/m2).
A8.6 The following is an example specification for salt contamination based on concentration measurements:
“Immediately prior to the application of the coating, the surface extract shall not contain more than xx µg/cm2 of the specific contaminant (e.g., chloride) when tested with a speci-fied method.”
A8.7 The following is an example specification for salt contamination based on conductivity measurements:
“Immediately prior to the application of the coating, the conductivity of the surface extract shall not exceed xx µS/cm when tested with a specified method.”
A9 Use of Corrosion Inhibitors: It may be advantageous to add corrosion inhibitors to the SP water or apply them to the surface immediately after waterjet cleaning to temporarily prevent rust formation. Some corrosion inhibitor treatments may interfere with the performance of certain coatings systems. The coatings manufacturer should be consulted to ensure the compatibility of corrosion inhibitors with the coatings.
A10 Specification Statement:
A10.1 The specifier should use the degree of surface cleanliness and one of the degrees of flash rust to specify the required end condition. The following are examples of a speci-fication statement:
“All surfaces to be recoated shall be waterjet cleaned to SSPC-SP WJ-4 L/NACE WJ-4/L, Light Cleaning, Light Flash Rust.”
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“At the time of the recoating, the degree of flash rust shall be no greater than moderate (M).”
A10.2 In addition, the specifier should consider whether a surface should be cleaned as required to achieve a particular, not to exceed maximum, level of nonvisible contamination (NV) prior to recoating. A suggested specification statement for nonvisible contamination (NV) is given in Paragraph A8.
A11 Flash Rust: An oxidation product that forms as a wetted carbon steel substrate dries. With the exception of stainless steel surfaces, any steel surface may show flash rust within 30 minutes or longer while the substrate is drying (water evaporation) after waterjet cleaning, depending on environmental conditions. Flash rust has the appearance of rust bloom. Flash rust quickly changes the appearance of the waterjet cleaned surface and may be reduced or eliminated by physical or chemical methods. The color of the flash rust may vary depending on the age and composition of the steel and the time-of-wetness of the substrate prior to drying. With time, the flash rust changes from a yellow-brown, well adherent, light rust to a red-brown, loosely adherent, heavy rust. Appendix B contains additional information on methods of assessing the degree of flash rust.
A12 Surface Imperfections:
A12.1 Surface imperfections that can cause premature failure are often present. Coatings tend to pull away from sharp edges and projections, leaving little or no coating to protect the underlying steel. Other features that are difficult to prop-erly cover and protect include crevices, weld porosities, and laminations.
A12.2 Poorly adhering fabrication defects, such as weld slag residues, loose weld spatter, and surface laminations may be removed during the waterjet cleaning operation. Other surface defects, such as steel laminations, weld porosities, or deep corrosion pits may not be evident until the surface prepa-ration has been completed. Therefore, proper planning for such surface repair work should be given prior consideration because the timing of the repairs may occur before, during, or after the waterjet cleaning operation. The SSPC-SP COM9
and NACE SP017810 contain additional information on surface imperfections.
A12.3 The high cost of the methods to remedy surface imperfections (e.g., edge rounding and weld spatter removal) should be compared with the benefits of preventing premature coating failure. Therefore, those responsible for establishing the requirements and those responsible for performing the work should agree on the procedures to be used to repair surface imperfections to the extent required in the procure-ment documents (project specification).
A13 Removal of Coatings with Hazardous Compo-nents—Hygiene: Waterjet cleaning is often used to remove coatings with hazardous components. Because the particles are wetted, respiratory protection requirements for waterjet
cleaning may be less stringent than for other methods of surface preparation. However, the wetted particles tend to stay on the skin. Applicable industrial hygiene tests should be performed to determine the destination of the wetted particles. Good industrial hygiene should be followed.
A14 Film Thickness: It is essential that ample coating be applied after waterjet cleaning to adequately cover the peaks of the surface profile. The dry film thickness of the coating above the peaks of the surface profile should equal the thickness known to be needed for the desired protection. If the dry film thickness over the peaks is inadequate, prema-ture rust-through or coating failure will occur. To ensure that coating thicknesses are properly measured, the procedures in SSPC-PA 211 for verification of accuracy of Type 1 and Type 2 gauges should be used.
Appendix BMethods of Assessing the Degree of Flash Rust(Nonmandatory)
This appendix is considered nonmandatory, although it
may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this stan-dard is not required to follow, but may choose to follow, any or all of the the provisions herein.
The degree of flash rust is related to the quantity of loose, clean rust dust that is present on the surface. One of the following alternative methods may be used to assess the degree of flash rust, or other methods may be used if specified.
B1 Wipe Test
The following procedure is suggested to standardize the amount of pressure used to perform a wipe test on a flash-rusted surface:
(a) Neatly wrap a white, lint-free, woven cloth around a standard 100 mm (4 in) nylon paint brush, and hold it in place in a manner that prevents the cloth from slipping.
(b) Swipe the cloth-wrapped paint brush across the flash-rusted surface in one motion, using pressure equivalent to that used to apply house paint to a door. The length of the swipe should be consistent (e.g., one pass covering 1,500 mm [6 in] in length).
(c) Remove the white cloth from the paint brush and evaluate the color and amount of rust on the cloth. “Recommended Guidelines for Evaluating Flash Rust,”12 issued by the NSRP, provides guidance to perform this evaluation of flash rust.
If lint deposition is a concern, the project specification may require use of an alternate technique to determine the degree of flash rust.
B2 Tape Pull Test
The tape pull test is a modification of the pressure-sensi-tive tape method in ISO 8502-3.13 The procedure is as follows:
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(a) Select a test area on the flash-rusted surface to perform the test.
(b) Place a 50 mm (2 in) long piece of tape (as specified in ASTM D 335914) on the selected test area and rub it thoroughly with a fingertip (not a fingernail) to ensure that the tape adheres firmly. Then peel the tape off the surface and place it on a piece of white paper for reference.
(c) Repeat the procedure in (b) nine times (for a total of 10 times) using a fresh piece of tape applied to the same spot on the surface (selected test area) each time.
(d) Assess the appearance of the 10th tape and the appearance of the test area on the flash-rusted surface after the 10th tape is pulled off in accordance with Table B1.
Appendix C: Waterjet Cleaning Equipment and Operating Parameters (Nonmandatory)
This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this stan-dard is not required to follow, but may choose to follow, any or all of the the provisions herein.
C1 Waterjet Cleaning Equipment
Multiple configurations of pumps, heads, and containment systems are suitable for waterjet cleaning operations. The equipment systems may include manual lances, fixed lances on platforms, or robot-driven systems. Additional descriptions relevant to waterjet cleaning systems are in the WaterJet Tech-nology Association’s “Recommended Practices for the Use of Manually Operated High-Pressure Waterjetting Equipment,”15 which also addresses concerns relevant to waterjet cleaning operations. The commercial waterjet cleaning unit can be mounted on a skid, trailer, or truck; can be equipped with various prime movers (diesel, electric motor, etc.); and usually consists of a pump, hoses, and various tools. The tools can be hand-held or mounted on a robot or controlled by a traversing
mechanism. Water is propelled through a single jet, fan jet, pulse generator, or multiple rotating jets. Rotation of the nozzle head is provided by small electric, air, or hydraulic motors, or by slightly inclined orifices in a multiple-orifice nozzle.
C1.1 All waterjet cleaning units normally use a hydraulic hose with a minimum bursting strength of 2.5 times the capa-bility of its maximum-rated operating strength.
C1.2 Waterjet streams are produced by orifices, or tips, that can have different forms–the higher the pressure, the more limited is the choice of forms. Round jets are most commonly used, but orifices of other shapes are available. Tips can be designed to produce multiple jets of water that are normally rotated to achieve higher material-removal rates. Interchangeable nozzle tips should be used to produce the desired streams. The manufacturer should be consulted for specific recommendations.
C1.3 Effect of Corrosion Inhibitors and Detergents on Equipment: If corrosion inhibitors are to be used with the SP water, the manufacturer of the waterjet cleaning equipment should be consulted to ensure compatibility of corrosion inhibi-tors with the equipment. Compatibility of detergents with the special seals and high-alloy metals of the waterjet cleaning equipment should be carefully investigated to ensure that the cleaning equipment is not damaged.
C2 Operating Parameters
C2.1 Waterjet Cleaning Method Selection: The person performing the work should have sufficient experience to select the waterjet cleaning method and the specific combination of water pressure and flow (velocity and volume) to achieve the specified degree of surface cleanliness. A water flow rate of 4 to 53 L/min (1 to 14 gal/min) is typical.
(a) LP WC or HP WC (the flow rate of the water is the dominant energy characteristic);
(b HP WJ (pressure or water velocity and flow rate are equally important); or
(c) UHP WJ (pressure or water velocity is the dominant energy characteristic).
TABLE B1ASSESSMENT OF DEGREE OF FLASH RUST—TAPE PULL TEST
Degree of Flash Rust Appearance of 10th Tape(after final pull from test area)
Appearance of Test Area (after 10th tape pull)
Light No rust on tape No change, or only slight change in test area appearance
Moderate Slight, localized red-brown rust on tapeSignificant change of test area appearance, showing localized areas of black rust
Heavy Significant, uniform red-brown rust on tape, also showing grains of black rust
Significant change of test area appearance, showing localized areas of black rust
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C2.2 Stand-off Distance: The distance from the nozzle to the work piece surface (stand-off distance) is critical for effec-tive cleaning with any of the waterjet cleaning methods. Typical stand-off distances for HP WJ and UHP WJ range from 25 to 150 mm (1.0 to 6.0 in) for coatings removal. Typical stand-off distances range up to 600 mm (24 in) to remove foreign matter that is not tightly adherent. Excessive stand-off distance does not produce the desired cleaning.
C2.3 Threshold Pressure: The threshold pressure of a coating can be determined. In general, the tougher, more resil-ient, or harder the coating (i.e., the more resistant to probing or cutting by a pocket knife), the higher the threshold pressure; the softer and more jelly-like the coating, the lower the threshold pressure. Threshold pressure is defined by Summers16 as the minimum required pressure to penetrate the material. Once the threshold pressure is achieved or exceeded, the produc-tion rate increases dramatically. Therefore, waterjet cleaning production rates can be classified according to two conditions:
(a) Relatively Slow—Erosion at pressures lower than the threshold pressure; and
(b) Relatively Fast—Waterjet cutting and erosion at pres-sures greater than the threshold pressure.
Pressure loss is a function of the flow rate of the water through the hose and the inside diameter of the hose. The manufacturer should be consulted for specific information on potential pressure loss for each type of equipment.
C2.4 Depending on the initial condition of the area and the materials to be removed, the choice of waterjet cleaning
method to achieve Light Cleaning (WJ-4) is ultimately based on the capabilities of the equipment and its components. Dwell time, traverse rate, pressure, flow, stand-off distances, the number of nozzles, and rotation speed all interact in deter-mining materials that remain and those that are removed.
C2.5 Reuse of Effluent Water: If effluent water is captured for reuse by the waterjet cleaning equipment, caution should be used to avoid introducing any removed contami-nants back onto the cleaned substrate. The effluent water may be placed in a clean holding tank and tested to determine the contaminant content prior to reintroduction into the water supply stream to the waterjet cleaning equipment. The effluent water should be monitored for suspended particulates, hydro-carbons, salts, hazardous materials, or other by-products of the surface preparation procedures.
C2.6 Additives: Any detergents, degreasers, or other types of cleaners used in conjunction with the waterjet cleaning method should be removed prior to applying a coating. If corro-sion inhibitors are to be used with the SP water, the coating manufacturer should be consulted to ensure compatibility of corrosion inhibitors with the coating.
C2.7 Containment Systems: Containment systems may consist of water-impermeable membranes or vacuum collec-tion heads or the systems described in SSPC-Guide 6.17 The containment design should consider the pressures used and water volumes produced and if the process may be open or closed loop (with a single pass or multiple passes of the water through the system)..
Designation: E 337 – 84 (Reapproved 1996) e1
Standard Test Method forMeasuring Humidity with a Psychrometer (the Measurementof Wet- and Dry-Bulb Temperatures) 1
This standard is issued under the fixed designation E 337; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e1 NOTE—Section 20 was added editorially in April 1996.
1. Scope
1.1 General:1.1.1 This test method covers the determination of the
humidity of atmospheric air by means of wet- and dry-bulbtemperature readings.
1.1.2 This test method is applicable for meteorologicalmeasurements at the earth’s surface, for the purpose of thetesting of materials, and for the determination of the relativehumidity of most standard atmospheres and test atmospheres.
1.1.3 This test method is also applicable when the tempera-ture of the wet bulb only is required. In this case, theinstrument comprises a wet-bulb thermometer only.
1.1.4 Relative humidity (rh) does not denote a unit. Uncer-tainties in the relative humidity are expressed in the formU 6u % rh, which means that the relative humidity is expected tolie in the range (U − u) % to (U + u) %, whereU is theobserved relative humidity. All uncertainties are at the 95 %confidence level.
1.2 Method A—Psychrometer Ventilated by Aspiration:1.2.1 This method incorporates the psychrometer ventilated
by aspiration. The aspirated psychrometer is more accuratethan the sling (whirling) psychrometer (see Method B), and itoffers advantages in regard to the space which it requires, thepossibility of using alternative types of thermometers (forexample, electrical), easier shielding of thermometer bulbsfrom extraneous radiation, accidental breakage, and conve-nience.
1.2.2 This method is applicable within the ambient tempera-ture range 5 to 80°C, wet-bulb temperatures not lower than1°C, and restricted to ambient pressures not differing fromstandard atmospheric pressure by more than 30 %.
1.3 Method B—Psychrometer Ventilated by Whirling (SlingPsychrometer):
1.3.1 This method incorporates the psychrometer ventilatedby whirling (sling psychrometer).
1.3.2 This method is applicable within the ambient tempera-ture range 5 to 50°C, wet-bulb temperatures not lower than 1°Cand restricted to ambient pressures not differing from standardatmospheric pressure by more than 30 %.
1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.(For more specificsafety precautionary statements, see 8.1 and 15.1.)
2. Referenced Documents
2.1 ASTM Standards:D 861 Practice for Use of the Tex System to Designate
Linear Density of Fibers, Yarn Intermediates, and Yarns2
D 1193 Specification for Reagent Water3
D 1356 Terminology Relating to Sampling and Analysis ofAtmospheres4
D 1357 Practice for Planning the Sampling of the AmbientAtmosphere4
D 3631 Test Methods for Measuring Surface AtmosphericPressure4
D 4023 Terminology Relating to Humidity Measurements4
D 4230 Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer4
E 1 Specification for ASTM Thermometers5
E 380 Practice for Use of the International System of Units(SI) (the Modernized Metric System)6
3. Terminology
3.1 Definitions:3.1.1 For definitions of humidity terms used in this test
method, refer to Terminology D 4023.3.1.2 For definitions of other terms in this test method, refer
to Terminology D 1356.3.2 Definitions of Terms Specific to This Standard:
1 This test method is under the jurisdiction of ASTM Committee D-22 onSampling and Analysis of Atmospheres and is the direct responsibility of Subcom-mittee D22.11 on Meteorology.
Current edition approved Nov. 30, 1984. Published June 1985. Originallypublished as E 337 – 31 T. Last previous edition E 337 – 62.
2 Annual Book of ASTM Standards, Vol 07.01.3 Annual Book of ASTM Standards, Vol 11.01.4 Annual Book of ASTM Standards, Vol 11.03.5 Annual Book of ASTM Standards, Vol 14.03.6 Annual Book of ASTM Standards, Vol 14.02. (Excerpts in all other volumes.)
1
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
3.2.1 Method A—Aspirated Psychrometer:3.2.1.1 aspiration—The wet and dry bulbs (and the psy-
chrometer) are described as aspirated because there is provi-sion for the forced ventilation by drawing air over the bulbs bysuction. The flow may be either transverse or parallel to theaxes of the bulbs.
3.2.1.2 thermometer—for purposes of this standard, andexcept where a specific type is indicated, the term thermometermeans any temperature-measuring device.
3.2.1.3 wet-bulb covering and wick—the wet bulb is pro-vided with a water-retaining covering of a woven-cottonmaterial. A cotton wick which connects the covering to a waterreservoir may be provided so that water is fed to the coveringcontinuously by capillarity.
3.2.2 Method B—Sling Psychrometer:3.2.2.1 ventilation—the wet and dry bulbs (and the psy-
chrometer) are described as ventilated because there is provi-sion for a flow of the air over the bulbs. The flow is transverseto the axes of the bulbs.
3.2.2.2 wet-bulb covering—the wet bulb is provided with awater-retaining covering of a woven-cotton material.
4. Summary of Methods
4.1 General:4.1.1 The wet-bulb temperature depression, the dry-bulb
temperature, and the ambient pressure provide the basis forderiving the relative humidity.
4.2 Method A—Aspirated Psychrometer:4.2.1 Establish the airflow (see 7.4) and maintain it until a
minimum wet-bulb temperature is attained. (With mercury-in-glass thermometers, about 2-min ventilation time is usuallynecessary.)
4.2.2 Read the thermometers with the necessary precision,obtaining the dry-bulb temperature with an overall uncertaintyof 60.2°C or better, and the temperature depression with anoverall uncertainty of60.2°C or better for an uncertainty in therelative humidity of63 % rh. For an uncertainty in the relativehumidity of 62 % rh, obtain the dry-bulb temperature with anoverall uncertainty of60.2°C or better and the temperaturedepression with an overall uncertainty of60.1°C or better.(Also see Section 12.)
4.3 Method B—Sling Psychrometer:4.3.1 Holding the instrument well away from the body, and
for outdoor measurements to windward and in the shade, whirlit at such a rate as to achieve the specified airspeed at the wetand dry bulbs, see 14.4.
4.3.2 Read the thermometers with the necessary precision,obtaining the dry-bulb temperature with an overall uncertaintyof 60.6°C or better, and the temperature depression with anoverall uncertainty of60.3°C or better for an uncertainty in therelative humidity of65 % rh, also see Section 19.
5. Significance and Use
5.1 The object of this test method is to provide guidelinesfor the construction of a psychrometer and the techniquesrequired for accurately measuring the humidity in the atmo-sphere. Only the essential features of the psychrometer arespecified.
METHOD A—PSYCHROMETER VENTILATEDBY ASPIRATION
6. Interferences
6.1 When an aspirated psychrometer is used for measure-ments in a small enclosed space and steadily rising wet- anddry-bulb temperatures are observed, consider whether heat andmoisture liberated by the instrument itself are affecting theconditions.
6.2 While the thermometers are being read, keep all surfacesthat are at temperatures other than the environment (such as thehands, face, and other warmer or colder objects) as far aspossible from the thermometer bulbs.
6.3 This method should not be used where there is heavycontamination of the air with gases, vapors, or dust.
7. Apparatus
7.1 Thermometers for an Aspirated Psychrometer:7.1.1 The range of the thermometers shall not exceed the
range 0 to 80°C. This range may be achieved by providingmore than a single pair of matched thermometers. When theuncertainty in the derived relative humidity is required to benot more than63 % rh, the thermometers shall be such thattheir readings give the temperature depression with an uncer-tainty of not more than60.2°C. When the uncertainty in therelative humidity is required to be not more than62 % rh, theyshall be such that their readings give the temperature depres-sion with an uncertainty of not more than60.1°C. Theuncertainty in the reading of the dry-bulb temperature shall benot more than60.2°C.
7.1.2 Electrical thermometers may be so connected that thereadings give the temperature depression and the dry-bulbtemperature directly.
7.1.3 Each thermometer shall consist of a temperaturesensor of essentially cylindrical shape which is supported on asingle stem, the stem being coaxial with the sensor. The freeend of each sensor shall be smoothly rounded. If the diameterof the stems is small, compared with that of the sensors, thenboth ends of each sensor shall be smoothly rounded. The sensorof a mercury-in-glass thermometer shall be that part of thethermometer extending from the bottom of the bulb to the topof the entrance flare of the capillary.
7.1.4 With transverse ventilation, the diameters of the sen-sors (excluding wet covering) shall be not less than 1 mm andnot greater than 4 mm.
7.1.5 With axial ventilation, the diameters of the sensors(excluding wet covering) shall be not less than 2 mm and notgreater than 5 mm, and their length not less than 10 mm andnot greater than 30 mm.
7.1.6 The connecting wires of electrical thermometers shallbe contained within the supporting stems and shall be isolatedfrom the moisture of the wet covering.
7.1.7 Mercury-in-glass shall be graduated to 0.5°C or closerand be capable of being read to the nearest 0.1°C or better. (Aspecification for mercury-in-glass thermometers suitable whenthe uncertainty in the derived relative humidity is required tobe not more than63 % rh is given in Annex A1.)
7.2 Wet-Bulb Covering, Wick, and Water Reservoir:7.2.1 The covering shall be fabricated from white-cotton
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muslin of linear density from 1.0 to 1.2 g/m, refer to PracticeD 861. A seamless sleeve is preferred, but a seam is permis-sible, provided that it does not add appreciably to the generalroughness which the weave imparts to the surface.
7.2.2 The covering shall completely cover the sensor orbulb of the thermometer, fit snugly but not very tightly, andshall be in physical contact with the bulb over its entire surface.It shall extend onto the stem for such a distance that the errorin the observed wet-bulb temperature due to heat conductionalong the stem does not exceed 0.05°C. (A method of deter-mining the distance for which the covering must extend ontothe stem is outlined in Annex A2. For mercury-in-glassthermometers with solid stems, a distance of twice the stemdiameter is usually adequate.)
7.2.3 To maintain a snugly fit cover on the wet bulb, thecovering may be secured with a cotton thread at the end of thecovering on the stem of the thermometer, at the top of thethermometer bulb, and at the bottom of the bulb. However,whenever a wicking is used, the covering shall not be securedbetween the thermometer bulb and the cotton wicking whichconnects the covering to a water reservoir.
7.2.4 After fabrication, the covering and wick shall havebeen washed in a dilute solution of sodium carbonate andthoroughly rinsed with distilled water. They shall not subse-quently be touched with the fingers.
7.2.5 The stem of each thermometer shall, for a lengthmeasured from the sensor and not less than 1.53 the length ofthe extension of the covering required by 7.2.2, be clear ofobstructions and freely exposed to the airstream.
7.2.6 During the test, the covering shall be completelypermeated with water as evidenced by a glistening appearancein a beam of light.
7.2.7 The covering shall be washed in situ with distilledwater from time to time and be renewed when it shows anyevidence of permanent change.
7.2.8 When a wick is provided, the free length of a wickshall be at least twice the diameter of the wet bulb and at leastthree times the wick diameter, ensuring that water arriving atthe covering is already at practically the wet-bulb temperature.A wick shall be limp.
7.2.9 A water reservoir shall not obstruct the airflow, and itscontents shall not affect the humidity of the sample air.
7.2.10 The level of the water in a water reservoir shall bebetween 5 and 25 mm below the level of the lowest part of thewet bulb.
7.3 Water—Reagent water shall be produced by distillation,or by ion exchange or reverse osmosis followed by distillation,refer to Specification D 1193.
7.4 Airflow:7.4.1 The flow of air over both the wet and dry bulbs shall
be a forced draught of 3 to 10 m/s for thermometers withmaximum allowable diameter of the sensors.
7.4.2 The sample air shall not pass over any obstruction orthrough a fan before it passes over the wet and dry bulbs.
7.4.3 With axial flow, the direction of the flow shall be fromthe free end of each sensor towards the support end.
7.4.4 No air which has been cooled by the wet bulb or by thewick shall impinge on the dry bulb.
7.5 Radiation Shields:7.5.1 Any radiation shields shall be of metal with a thick-
ness of 0.4 to 0.8 mm. Surfaces required to have a polishedfinish shall be of a bare metal which will retain its brightness.
7.5.2 With transverse ventilation, radiation shields may beprovided to shield the wet and dry bulbs from extraneousradiations. The radiation shields, essentially in the form ofparallel plates, can be either polished on the outside andblackened on the inside, or polished on both the inside andoutside surfaces. The clearance between the wet and dry bulbsand the shields shall be not less than half the overall diameterof the wet bulb. The shields shall be liberally flared outwardsat the inlet to prevent the flow separating from the shields onthe inside (vena-contracta effect). The shields may form part ofa duct for the airflow. A second shield, outside, is not necessary.
7.5.3 With axial ventilation, concentric radiation shieldsshall be provided for the wet and dry bulbs, and shall bepolished inside and out. (The shield around the wet bulb playsa vital role in reducing the radiative heat transfer between thatbulb and its surroundings by a factor of about three.) Thediameter of the shield shall be not less than 1.8d and notgreater than 2.5d, whered is the overall diameter of the wetbulb. Its length and position shall be such that its projectionbeyond each end of the wet covering is not less thand and notgreater than 3d. The entrance to the shield shall be liberallyflared to form a bell-mouth to prevent the flow separating fromthe shield on the inside. The shield may serve also as the ductfor the airflow. A second shield, outside, is not necessary.
8. Precautions
8.1 Safety Precautions—Mercury vapor is poisonous, evenin small quantities, and prolonged exposure can produceserious physical impairment(1).7 If a mercury thermometer isaccidentally broken, carefully collect, place, and seal all of themercury in a strongly made nonmetallic container. Avoid skincontact with mercury.
8.2 Technical Precautions—For reliable measurement andcontrol, strict adherence to the exacting technique is necessary.Aside from the obvious mistake of not using a psychrometricchart or table prepared for the existing barometric pressure,most errors of psychrometry tend to restrict lowering of thewet-bulb temperature and thus indicate a higher relativehumidity than actually exists.
8.2.1 Conditions which Contribute to High Wet-Bulb Tem-perature:
8.2.1.1 Improper installation of wet-bulb covering (loosefitting, too short, or too long).
8.2.1.2 Dirty or contaminated covering.8.2.1.3 Contamination of wetting water.8.2.1.4 Insufficient air flow.8.2.1.5 Failure to reach or read the minimum point of the
wet-bath depression.8.2.1.6 Moisture or heat generation, or both, from the
operator taking readings and from the wet-bulb water reservoir.8.2.1.7 Radiant heating effects.
7 The boldface numbers in parentheses refer to the list of references at the endof this test method.
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8.2.2 Heat from the fan or motor shall not affect thethermometer readings.
8.2.3 Instrument shall be used in the shade and not exposedto direct sunlight.
8.2.4 Prior to a measurement, the instrument shall have beenexposed long enough to the test atmosphere to have attainedthe ambient temperature.
8.2.5 The shield shall not be allowed to become wetted.
9. Calibration
9.1 The thermometers used in a psychrometer should becompared once a year at four or more temperatures with thecovering removed from the wet-bulb thermometer. Once everythree months, the thermometers should be compared, with thecovering removed from the wet-bulb thermometer, at theambient dry-bulb temperature. The readings shall conform tothe requirements (see 7.1.1 and Section 12) when the instru-ments are totally immersed. For highest accuracy, the ther-mometers should be calibrated over their range of use whiletotally immersed. The corrections thus determined should beapplied to the readings when making a measurement.
10. Procedure
10.1 Location—Avoid locations where proximity to ma-chinery, direct heat from the sun, or other sources of radiationwould have undue influence. Stand preferably facing the aircurrent so that the instrument receives the air before the air haspassed near you. The site or location is selected so that the airis a representative sample. (Also see Practice D 1357.)
10.2 Preparing Psychrometer—Moisten the covering of thewet bulb thoroughly with distilled water. (Before the start of aseries of measurements, deliver an excess of clean waterdirectly to the wet-bulb covering from the reduced tip of aclean glass or plastic tube which is a part of a small washbottle, for example, squeeze bottle, so that drops of water fallfrom the covering. This flooding procedure will help to removeorganic contamination which may be on the surface of thewet-bulb covering.) Wetting should be repeated before eachseparate measurement. A small bottle or porous porcelain cupwill serve as a convenient water container. If new or drythrough disuse, several minutes may be required for completesaturation of the fabric. Avoid touching the fabric with thefingers, which may deposit oil or dirt. Replace soiled coveringand wick. Maintain the dry bulb absolutely dry.
10.3 Aspirating the Psychrometer—Operate the fan motor,thus exposing the thermometers to the action of the air until theminimum wet-bulb temperature is indicated. Continue operat-ing the fan until the readings of the thermometers becomeconstant.
10.3.1 Reading Psychrometer—While operating the fan,read the thermometers quickly but carefully. Read the wet bulbfirst. Under ordinary conditions, an approximate 0.15°C errorin wet-bulb depression results in a 1 % error in relativehumidity. While the thermometers are being read, keep allsurfaces that are at temperatures other than the environment(such as the hands, face, and either warmer or colder objects)as far as possible from the thermometer bulbs.
10.3.2 For measurements in nominally constant conditions,for example, where fluctuation period is long compared with
the measurement time, repeat steps 10.3 and 10.3.1, rewettingthe covering if necessary, until in three successive readings thegreatest temperature depression differs from the least by notmore than 0.2°C for an uncertainty of63 % rh or not morethan 0.1°C for an uncertainty of62 % rh.
10.3.3 Where measurements are being made under condi-tions fluctuating rapidly, take a number of readings over at leasttwo complete cycles.
10.3.4 Where measurements are being made while condi-tions are changing or are being changed under control, thereadings might not be meaningful.
10.4 Check Readings—For purposes of checking, make asmany readings as necessary until three successive readingsagree. If atmospheric conditions are fluctuating, it may bedesirable to obtain several readings in order to secure anaverage (that is, if there is a definite cycling in conditions, thenreadings should be continued for at least two cycles). It will benecessary to rewet the covering of the wet bulb when the fabricstarts to dry, as indicated by a rising wet-bulb temperature.
11. Calculation
11.1 Subtract the wet-bulb reading from the dry-bulb read-ing. The difference is thewet-bulb depression. Knowing thedry-bulb temperature and the wet-bulb depression, the relativehumidity could be calculated by using the basic psychrometricequation. In practice, calculations directly involving the basicequation are seldom needed. Instead, tables, charts, curves, andother calculating devices developed from the basic equation areused, such as the table in Appendix X3.
11.2 When calculating relative humidity from the psychro-metric equation, use the following equation or one that for theprevailing conditions is equivalent:
e5 ew ~tw! 2 Ap~t 2 tw! (1)
where:e = the partial pressure of water vapor in the atmo-
sphere, Pa,ew (tw) = the saturation pressure of water vapor at the
wet-bulb temperaturetw, Pa, see Appendix X2,t = the dry-bulb temperature in °C,tw = the wet-bulb temperature in °C,p = the total (atmospheric) pressure, Pa, see Test
Methods D 3631,A = the psychrometer coefficient in K−1, and
wheree, ew(tw) and p are expressed in the same units, seePractice E 380.
11.2.1 The value ofA shall be chosen in the range6.23 10−4 to 6.93 10−4 k−1. The psychrometer coefficientdeveloped by Ferrel,A = 6.63 10−4(1 + 0.00115 tw), fallswithin this range. If a value ofA has been determined for theparticular design of psychrometer and lies in this range, then itshall be used. If a value has been determined but lies outsidethis range, then the closer extreme value of the range shall beused. If no value ofA has been determined, then use the valuedeveloped by Ferrel. (It may be noted that if, for example, at20°C and standard atmospheric pressure use of the value6.53 10−4 K−1 led to a derived relative humidity of 50.0 %,then use of the value 6.93 10−4 K−1 would lead to a derived
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relative humidity of 48.9 %.)11.3 Relative Humidity—The psychrometric equation gives
the partial pressure of the water vapor. In the meterologicalrange of pressure and temperature, the saturation vapor pres-sure of the pure water phase and of the moist air will beassumed to be equal. (Water vapor and air mixture is assumedto behave as ideal gas.) This assumption will introduce an errorof approximately 0.5 % or less in the calculated partial pressureof water vapor and an error of less than 0.5 % in the calculatedrelative humidity. (See Test Method D 4230.) If water vaporand air are assumed to behave as ideal gases, then
U 5 ees 3 100 % (2)
where:e = the partial pressure of the water vapor andes = the saturation vapor pressure of water at the dry-bulb
temperature, see Appendix X2.11.4 Use of Psychrometric Table or Chart:11.4.1 Take a psychrometric table or chart, the values in
which are consistent with the equations and appropriate valueof the psychrometer coefficientA as given in 11.2, and from thedry-bulb temperature and the temperature depression obtain therelative humidity or the humidity in whatever desired measure.(To facilitate the identification of suitable tables or charts,values of relative humidity for various dry-bulb temperaturesand temperature depressions are given in Appendix X1 forstandard atmospheric pressure and three relevant values ofA,namely 6.53 10−4, 6.73 10−4, and 6.93 10−4 K−1.)
11.4.2 In Appendix X3, values of relative humidity fordry-bulb temperatures 2 to 50°C and various temperaturedepressions are given for standard atmospheric pressure(101325 Pa) and using Ferral’s value forA[6.603 10−4(1 + 0.00115tw)].
11.4.3 In cases where the barometric pressure differs fromstandard atmospheric pressure, the corrections that are to beapplied to the values of relative humidity listed in Appendix X3are given in Appendix X4.
12. Precision and Bias
12.1 The uncertainty in the derived relative humidity isestimated not to exceed the values shown in Table 1 if thetemperature depression and the dry-bulb temperature measure-ment do not exceed the uncertainty values shown in Table 1.
METHOD B—PSYCHROMETER VENTILATED BYWHIRLING (SLING PSYCHROMETER)
13. Interferences
13.1 (See 6.2 and 6.3.)
14. Apparatus
14.1 Thermometers for Sling Psychrometers:14.1.1 The thermometers shall be mercury-in-glass ther-
mometers.14.1.2 The range of the thermometers shall not exceed the
range 0 to 50°C; however, this range may be achieved byproviding more than a single pair of matched thermometers.When the uncertainty in the derived relative humidity isrequired to be not more than65 % rh, the thermometers shallbe such that their readings give the temperature depressionwith an uncertainty of not more than60.3°C and the uncer-tainty in the reading of the dry-bulb temperature shall be notmore than6 0.6°C. When the uncertainty in the derivedrelative humidity is required to be not more than63 % rh, thethermometers shall be such that their readings given thetemperature depression and the dry-bulb temperature with anuncertainty of not more than60.2°C.
14.1.3 The diameters of the thermometer bulbs (excludingwet covering) shall be not greater than 4 mm.
14.1.4 (See 7.1.7.)14.2 Wet-Bulb Covering:14.2.1 (See 7.2.1.)14.2.2 The covering shall completely cover the sensor or
bulb of the thermometer, fit snugly but not very tightly, andshall be in physical contact with the bulb over its entire surface.It shall extend onto the stem for such a distance that the errorin the observed wet-bulb temperature due to heat conductionalong the stem does not exceed 0.05°C. For mercury-in-glassthermometers with solid stems, a distance of twice the stemdiameter is usually adequate.
14.2.3 To maintain a snugly fit cover on the wet bulb, thecovering may be secured with a cotton thread at the end of thecovering on the stem of the thermometer, at the top of thethermometer bulb, and at the bottom of the bulb.
14.2.4 (See 7.2.4.)14.2.5 The stem of each thermometer shall, for a length
measured from the sensor and not less than 1.53 the length ofthe extension of the covering required by 14.2.2, be clear ofobstructions and freely exposed to the airstream.
14.2.6 (See 7.2.6 and 7.2.7.)14.3 Water—(See 7.3.)14.4 Airflow:14.4.1 The psychrometer shall be whirled so that the flow of
air over both the wet and dry bulbs is equivalent to 3 to 10 m/sfor thermometers with maximum allowable diameter of thesensors.
14.4.2 The sample air shall not pass over any obstructionbefore it passes over the wet and dry bulbs.
14.4.3 (See 7.4.4.)14.5 Radiation Shields—Radiation shields are not neces-
sary.
15. Precautions
15.1 Safety Precautions:15.1.1 Mercury vapor is poisonous, even in small quantities,
and prolonged exposure can produce serious physical impair-ment (1), see 8.1.
TABLE 1
Uncertainty inDerived RelativeHumidity, %, rh
Uncertainty inTemperature
Depression, °C
Uncertainty inDry-bulb
Temperature,° C
64 60.3 60.263 60.2 60.262 60.1 60.265 60.3 60.664 60.2 60.663 60.1 60.6
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15.1.2 Before using a sling psychrometer, check for ad-equate clearance to freely sling or whirl the thermometerswithout hitting any solid surfaces; for example, the knee.
15.1.3 If a mercury thermometer is accidentally broken,follow the handling procedure in 8.1.
15.2 Technical Precautions—(See 8.2.)15.2.1 Conditions which Contribute to High Wet-Bulb
Temperature—(See 8.2.1.1-8.2.1.7.)15.2.2 (See 8.2.3 and 8.2.4.)
16. Calibration
16.1 The thermometers used in a psychrometer should becompared once a year at four or more temperatures with thecovering removed from the wet-bulb thermometer. Once everythree months, the thermometers should be compared, with thecovering removed from the wet-bulb thermometer, at theambient dry-bulb temperature. The readings shall conform tothe requirements, (see 14.1.2 and Section 19) when theinstruments are totally immersed. For highest accuracy, thethermometers should be calibrated over their range of usewhile totally immersed. The corrections thus determinedshould be applied to the readings when making a measurement.
17. Procedure
17.1 Location—(See 10.1.)17.2 Preparing Psychrometer—(See 10.2.)17.3 Ventilating the Psychrometer—Holding the instrument
well away from the body, and for outdoor measurements towindward and in the shade, whirl it at such a rate as to achievethe specified airspeed at the wet and dry bulbs (see 14.4) andthen stop the motion after 30 s to read the thermometers.Resume whirling for an additional 10 s before stopping themotion to read the thermometers. Continue this procedure ofwhirling for 10 s, rewetting the covering if necessary (see10.4), until a minimum wet-bulb temperature has been at-tained. (About 2-min ventilation time is usually necessary.)
17.3.1 Reading Psychrometer—After whirling the psy-chrometer, read the thermometers quickly but carefully. Readthe wet bulb first. Under ordinary conditions, an approximate0.3°C error in wet-bulb depression results in a 2 % error inrelative humidity. While the thermometers are being read, keepall surfaces that are at temperatures other than the environment(such as the hands, face, and either warmer or colder objects)as far as possible from the thermometer bulbs.
17.3.2 For measurements in nominally constant conditions,for example, where a fluctuation period is long compared withthe measurement time, repeat Steps 17.3 and 17.3.1, rewettingthe covering if necessary, until in three successive readings thegreatest temperature depression differs from the least by notmore than 0.3°C for an uncertainty of65 % rh.
17.3.3 (See 10.3.3 and 10.3.4.)17.4 Check Readings—(See 10.4.)
18. Calculation—(See Section 11.)
19. Precision and Bias
19.1 The uncertainty in the derived relative humidity isestimated not to exceed the values shown in Table 2 if thetemperature depression and the reading of the dry-bulb tem-perature do not exceed the uncertainty values shown in Table 2.
20. Keywords
20.1 aspiration; humidity; psychrometer; psychrometrictable; temperature; vapor pressure; ventilation; wet-bulb tem-perature
ANNEXES
(Mandatory Information)
A1. MERCURY-IN-GLASS THERMOMETERS SUITABLE WHEN THE UNCERTAINTY IN THEMEASURED RELATIVE HUMIDITY IS REQUIRED NOT TO EXCEED 63 % RH
A1.1 Mercury-in-glass thermometers conforming to thefollowing specification are suitable when the uncertainty in themeasured relative humidity is required not to exceed63 % rh.
A1.1.1 Type—The thermometers shall be of the solid-stemtype, and the stem may have a slight neck near the bulb toallow the wet-bulb covering to be secured more easily by acotton thread.
A1.1.2 Temperature Scale—The thermometers shall begraduated for total immersion and in accordance with theCelsius scale which corresponds with the International Practi-cal Temperature Scale of 1968.
A1.1.3 Range—The nominal temperature range of the ther-mometers shall be 0 to 80°C for an aspirated psychrometer and
0 to 50°C for a sling psychrometer.A1.1.4 Materials—The stem shall be made of suitable
thermometer glass with an enamel back. The bulb shall bemade of glass meeting the Specification E 1.
A1.1.5 Annealing and Stabilization—The glass shall besuitably annealed, and the thermometers shall be stabilized bya suitable heat treatment before they are filled with mercury.
A1.1.6 Expansion Chamber—Each thermometer shall in-clude an expansion chamber above the highest scale line so thata temperature of at least 100°C can be sustained without thelikelihood of damage.
A1.1.7 Dimensions:
TABLE 2
Uncertainty inDerived RelativeHumidity, %, rh
Uncertainty inTemperature
Depression, °C
Uncertainty inDry-bulb
Temperature,° C
64 60.3 60.263 60.2 60.265 60.3 60.664 60.2 60.6
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mmLength from bottom of bulb to underside of button or ring
top (maximum)240
Scale length corresponding to the nominal range(minimum)
130
Bulb lengthA 10 to 30Bulb diameter 3 to 4Stem diameter 4 to 5Distance of neck (if any) from top of bulbA 8 to 12Distance of lowest scale line from top of bulbA (min) 30Distance of expansion chamber from highest scale line
(min)10
________________AThe top of the entrance flare of the capillary is taken to be the top of the bulb.
A1.1.8 Graduation and Figuring—The thermometers shallbe graduated at each 0.5°C, with a spacing of approximately 2
mm and with a longer line at each 1°C. The graduations shallbe numbered at each 5°C.
A1.1.9 Accuracy—Readings of each thermometer made bya knowledgeable and experienced observer with the thermom-eters totally immersed shall not be in error by more than 0.2°Cfor any temperature in the nominal range. For any twotemperatures in the nominal range, readings of the two ther-mometers, so made, shall give the difference of the tempera-tures with an error not exceeding 0.2°C.
A1.1.10 Spare Thermometer—If a third thermometer isassociated with the psychrometer, then A1.1.9 shall apply toeach of the three possible combinations of two thermometers.
A2. DETERMINATION OF THE DISTANCE FOR WHICH THE WET-BULB COVERING MUST EXTEND ONTO THETHERMOMETER STEM TO LIMIT THE HEAT-CONDUCTION ERROR TO 0.05°C
A2.1 Temporarily fit the bulbs (sensors) of both thermom-eters with coverings similar to that to be used on the wet bulb,but allow the coverings to extend onto the stems considerablyfurther than usual, say 1.53, the usual distance.
A2.2 Operate the instrument in the usual manner but withboth coverings wet, choosing a location where the conditionsare steady. Observe the difference of the thermometer readingsas accurately as possible. (This difference is due mainly to theerrors of the thermometers themselves.)
A2.3 Progressively reduce the extension of one of thecoverings onto the stem until the difference of the readings ofthe thermometers is estimated to have changed by 0.05°C. Theextension existing at that stage is the minimum permissible.
A2.4 A more accurate determination can be made if thedifference of the readings is plotted against the extension for anumber of extensions both greater than and less than thatcorresponding to a change of 0.05°C. The minimum extension
which corresponds to a change of this amount may then easilybe read from the plot.
A2.5 During the procedure, as in normal operation of thepsychrometer, care must be taken to preserve the cleanliness ofthe coverings, and in particular to avoid touching them with thefingers.
A2.6 The procedure determines the extension necessary forthe conditions which prevail at the time. If it is carried outunder conditions which differ substantially from those underwhich the psychrometer is normally used, then allowanceshould be made for the fact that for a given extension of thecovering the temperature error due to the heat conduction isroughly proportional to the temperature depression. For ex-ample, if the present procedure is carried out under atmo-spheric conditions such that the temperature depression istwice the value which occurs in the normal use of theinstrument, then the extension which results in a change of0.1°C in the temperature difference is the required minimum.
APPENDIXES
(Nonmandatory Information)
X1. SKELETON TABLE OF RELATIVE HUMIDITIES
X1.1 Relative humidities rounded to the nearest 0.5 % rhare tabulated for various temperatures and temperature depres-sions and for standard atmospheric pressure and three values ofthe psychrometer coefficient. Table X1.1 is given so that othermore detailed tables may be compared with it. The dry-bulbtemperature interval of 10°C and the temperature depressioninterval of 2°C are too wide to allow the table to be used forroutine humidity measurement. The saturation vapor pressure
of water has been taken from A. Wexler, Appendix X2.Standard atmospheric pressure is 1.013253 105 Pa.
ValuesUpper A = 6.5 3 10−4 K−1
Intermediate A = 6.7 3 10−4
Lower A = 6.9 3 10−4
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Designation: D 4414 – 95 (Reapproved 2001)
Standard Practice forMeasurement of Wet Film Thickness by Notch Gages 1
This standard is issued under the fixed designation D 4414; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice describes the use of thin rigid metalnotched gages, also called step or comb gages, in the measure-ment of wet film thickness of organic coatings, such as paint,varnish, and lacquer.
1.2 Notched gage measurements are neither accurate norsensitive, but they are useful in determining approximate wetfilm thickness of coatings on articles where size(s) and shape(s)prohibit the use of the more precise methods given in MethodsD 1212.
1.3 This practice is divided into the following two proce-dures:
1.3.1 Procedure A—A square or rectangular rigid metalgage with notched sides is used to measure wet film thick-nesses ranging from 3 to 2000 µm (0.5 to 80 mils 1). Such agage is applicable to coatings on flat substrates and to coatingson articles of various sizes and complex shapes where it ispossible to get the end tabs of the gage to rest in the same planeon the substrate.
1.3.2 Procedure B—A circular thin rigid metal notched gageis used to measure wet film thicknesses ranging from 25 to2500 µm (1 to 100 mils ). Such a gage is applicable to coatingson flat substrates and to coatings on objects of various sizes andcomplex shapes.
1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.
1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:D 1212 Test Methods for Measurement of Wet Film Thick-
ness of Organic Coatings2
3. Summary of Practice
3.1 The material is applied to the articles to be coated andthe wet film thickness measured with a notched gage.
3.2 Procedure A—A square or rectangular thin rigid metalgage with notched sides, having tabs of varying lengths, ispushed perpendicularly into the film. After removal from thefilm, the gage is examined and the film thickness is determinedto lie between the clearance of the shortest tab wet by the filmand the clearance of the next shorter tab not wetted by the film.
3.3 Procedure B—A circular thin rigid metal gage havingspaced notches of varying depths around its periphery is rolledperpendicularly across the film. After removal from the film,the gage is examined and the film thickness is determined asbeing between the clearance of the deepest face wetted and theclearance of the next deepest notch face not wetted by the film.
4. Significance and Use
4.1 Wet film thickness measurements of coatings applied onarticles can be very helpful in controlling the thickness of thefinal dry coating, although in some specifications the wet filmthickness is specified. Most protective and high performancecoatings are applied to meet a requirement or specification fordry film thickness for each coat or for the completed coatingsystem, or for both.
4.2 There is a direct relationship between dry film thicknessand wet film thickness. The wet film/dry film ratio is deter-mined by the volume of volatiles in the coating as applied,including permitted thinning. With some flat coatings the dryfilm thickness is higher than that calculated from the wet filmthickness. Consequently, the results from the notch gage arenot to be used to verify the nonvolatile content of a coating.
4.3 Measurement of wet film thickness at the time ofapplication is most appropriate as it permits correction andadjustment of the film by the applicator at the time ofapplication. Correction of the film after it has dried orchemically cured requires costly extra labor time, may lead tocontamination of the film, and may introduce problems ofadhesion and integrity of the coating system.
4.4 The procedures using notched gages do not provide asaccurate or sensitive measurements of wet film thickness as dothe Interchemical and Pfund gages described in MethodsD 1212. Notch gages may, however, be used on nonuniformsurfaces, like concrete block, that are too rough to use the
1 This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.
Current edition approved Nov. 10, 1995. Published January 1996. Originallypublished as D 4414 – 84. Last previous edition D 4414 – 84 (1990)e1.
2 Annual Book of ASTM Standards, Vol 06.01.
1
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
Interchemical and Pfund gages. Also notched gages can bevery useful in the shop and field for determining the approxi-mate thickness of wet films over commercial articles wheresize(s) and shape(s) are not suitable for measurements by othertypes of gages. Examples of such items are ellipses, thin edges,and corners.
4.5 An operator experienced in the use of a notched gagecan monitor the coating application well enough to ensure theminimum required film thickness will be obtained.
4.6 Application losses, such as overspray, loss on transfer,and coating residue in application equipment, are a significantunmeasurable part of the coating used on a job and are notaccounted for by measurement of wet film thickness.
5. Report
5.1 Report the following information:5.1.1 The mean and range of the readings taken and the
number of readings.5.1.2 The smallest graduation of the gage used.
6. Precision and Bias
6.1 The precision and bias of Procedure A or B for measur-ing wet film thickness with notch gages are very dependent onmethods of film application, time that the measurement is takenafter film application, mechanical condition of the notch gages,and the step range of the gages.
6.2 Generally, the agreement between notch gages is goodbecause they are insensitive to small differences in filmthickness, that is the step intervals of the gages are relativelylarge.
PROCEDURE A
7. Apparatus
7.1 Notched Gage, square or rectangular, thin rigid metalplate, with notched sides (see Fig. 1), made from steel oraluminum3 (Note 1). Nonmetallic gages shall not be used.
NOTE 1—Aluminum or aluminum alloy gages are more easily distortedand may exhibit greater wear than steel gages. Gages made of plastic ordeformable metal are not suitable.
7.1.1 Each notched side shall consist of a series of tabs(between notches) varying in length and located in a linebetween two end tabs equal in length and longest in the row.
7.1.2 As an example, the tabs on one row of a gage maydiffer in length as follows:
By 13 µm ( 0.5 mil) between 0 to 150 µm (0 and 6 mils),By 25 µm (1 mil) between 150 to 250 µm (6 and 10 mils),By 50 µm (2 mils) between 250 to 750 µm (10 and 30 mils),andBy 125 µm(5 mils) over 750 µm (30 mils).
8. Procedure
8.1 Apply the coating material to a rigid substrate and testwith the gage immediately. The gage must be used immediatelyfollowing application of the coating. Some coatings losesolvents quickly and spray application increases the speed. Theresulting rapid reduction in wet film thickness can causemisleading readings.
8.2 Locate an area sufficiently large to permit both end tabsof the gage to rest on the substrate in the same plane.
8.3 Push the gage perpendicularly into the wet film so thatthe two end tabs rest firmly on the substrate at the same time.
8.4 Or, set one end tab firmly on the substrate and lower thegage until the other end tab is firmly in contact with thesubstrate.
8.5 Remove the gage from the film and examine the tabs.The film thickness is determined as being between the clear-ance of the shortest tab wettedd and the clearance of the nextshorter tab not wetted by the film.
8.6 Clean the gage immediately after each reading bywiping it on a dry or solvent-dampened cloth so that subse-quent readings are not affected. Do not clean with metalscrapers.
8.7 Repeat the procedure in 8.2-8.5 for at least threelocations on the film. The number of readings required toobtain a good estimate of the film thickness varies with theshape and size of the article being coated, with the operator’sexperience, and whether one or more of the following prob-lems are encountered:
8.7.1 Some coatings may not wet (leave residue on) somemetal gages. However, the film itself may show where contactwas made. When reading the gage, look at both the gage andthe film itself for verification of the reading.
8.7.2 The gage may slip on the surface. Ignore such read-ings.
8.7.3 The surface may be coarse and false readings pro-duced. The spot where the gage is used must be as uniform aspossible and questionable readings ignored.
8.8 Determine the mean and range of the readings.
9. Report
9.1 Report the mean and range of the readings.
PROCEDURE B
10. Apparatus
10.1 Circular Notched Gage,4 thin metal disk, with cali-brated notches of various depths spaced around its periphery
3 These gages are commercially available from various coating equipment andinstrument suppliers.
4 The “Hotcake” Wet Film Thickness Gage is covered by a patent held by PaulN. Gardner, Sr., 316 N.E. First Street, Pompano Beach, FL 33060. Interested partiesare invited to submit information regarding the identification of acceptable alterna-tives to this patented item to the Committee on Standards, ASTM Headquarters, 100Barr Harbor Drive., West Conshohocken, PA 19428. Your comments will receivecareful consideration at a meeting of the responsible technical committee, whichyou may attend.
FIG. 1 Rectangular Notched Gage
D 4414
2
(see Fig. 2). Each notch has a recessed flat face. A hole is in thecenter of the disk.
10.2 Examples of the scale increments and ranges providedby the notches are:
10.2.1 25–µm increments between 25 µm to 100 µm (1 to 4mils),
10.2.2 50–µm increments between 150 µm to 1500 µm (6and 60 mils), and
10.2.3 100–µm increments between 1500 µm to 2000 µm(60and 80 mils ).
11. Procedure
11.1 Select a gage that has a segment with a thickness scaleappropriate for the expected range of wet-film thickness.
11.2 Locate areas on the rigid substrate sufficiently large topermit the gage to roll for at least 11⁄2 in. (40 mm).
11.3 Apply the liquid coating to the substrate and immedi-ately place the selected segment perpendicularly on the wetfilm and in firm contact with the substrate. Roll the gage acrossthe film, holding the disk with a thumb and index finger in thecenter hole.
11.4 Remove the gage from the film and inspect the notchfaces. The wet-film thickness is determined as being betweenthe clearance of the deepest notch face wetted and theclearance of the next deeper notch face not wetted by the film.
11.5 Clean the gage immediately after each reading bywiping on a dry or solvent-dampened cloth so that subsequentreadings are not affected. Do not clean with metal scrapers.
11.6 Repeat the procedure from 11.1-11.5 as described in8.7.
11.7 Determine the mean and range of the readings.
12. Report
12.1 Report the mean and range of the readings.
13. Keywords
13.1 circular notched gage; rectangular notched gage
The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connectionwith any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any suchpatent rights, and the risk of infringement of such rights, are entirely their own responsibility.
This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make yourviews known to the ASTM Committee on Standards, at the address shown below.
This standard is copyrighted by ASTM, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above address or at610-832-9585 (phone), 610-832-9555 (fax), or [email protected] (e-mail); or through the ASTM website (www.astm.org).
FIG. 2 Circular Notched Gage
D 4414
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Designation: D 4417 – 93 (Reapproved 1999)
Standard Test Methods forField Measurement of Surface Profile of Blast CleanedSteel1
This standard is issued under the fixed designation D 4417; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 These test methods cover the description of techniquesfor measuring the profile of abrasive blast cleaned surfaces inthe laboratory, field, or in the fabricating shop. There areadditional techniques suitable for laboratory use not covered bythese test methods.
1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.
1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of whoever uses this standard to consult andestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.
2. Summary of Test Method
2.1 The methods are:2.1.1 Method A—The blasted surface is visually compared
to standards prepared with various surface profile depths andthe range determined.
2.1.2 Method B—The depth of profile is measured using afine pointed probe at a number of locations and the arithmeticmean determined.
2.1.3 Method C—A composite plastic tape is impressed intothe blast cleaned surface forming a reverse image of the profile,and the maximum peak to valley distance measured with amicrometer.
3. Significance and Use
3.1 The height of surface profile has been shown to be afactor in the performance of various coatings applied to steel.For this reason, surface profile should be measured prior tocoating application to ensure that it meets that specified. Theinstruments described are readily portable and sufficientlysturdy for use in the field.
NOTE 1—Optical microscope methods serve as a referee method forsurface profile measurement. Profile depth designations are based on the
concept of mean maximum profile (h̄ max); this value is determined byaveraging a given number (usually 20) of the highest peak to lowest valleymeasurements made in the field of view of a standard measuringmicroscope. This is done because of evidence that coatings performancein any one small area is primarily influenced by the highest surfacefeatures in that area and not by the average roughness.2
4. Apparatus
4.1 Method A—A profile comparator consisting of a numberof areas (each approximately one square inch in size), usuallyside by side, with a different profile or anchor pattern depth.Each area is marked giving the nominal profile depth in mils ormicrometres. Typical comparator surfaces are prepared withsteel shot, steel grit, or sand or other nonmetallic abrasive,since the appearance of the profile created by these abrasivesmay differ. The comparator areas are used with or withoutmagnification of 5 to 10 power.
4.2 Method B—A dial gage3 depth micrometer fitted with apointed probe. The probe is machined at a 60° angle with anominal radius of 50 µm. The base of the instrument rests onthe tops of the peaks of the surface profile while the springloaded tip projects into the valleys.
4.3 Method C—A special tape4 containing a compressiblefoam attached to a noncompressible uniform plastic film. Aburnishing tool is used to impress the foam face of the tape intothe surface to create a reverse replica of the profile that ismeasured using a spring-loaded micrometer.
5. Test Specimens
5.1 Use any metal surface that, after blast cleaning, is free of
1 These test methods are under the jurisdiction of ASTM Committee D-1 on Paintand Related Coatings, Materials, and Applications and are the direct responsibilityof Subcommittee D01.46 on Industrial Protective Painting.
Current edition approved May 15, 1993. Published July 1993. Originallypublished as D 4417 – 84. Last previous edition D 4417 – 84.
2 John D. Keane, Joseph A. Bruno, Jr., Raymond E. F. Weaver, “Surface Profilefor Anti-Corrosion Paints,” Oct. 25, 1976, Steel Structures Painting Council, 4400Fifth Ave., Pittsburgh, PA 15213.
3 The sole source of supply of suitable depth micrometers known to thecommittee at this time is the surface profile gage, Model 123, Elcometer Instru-ments, Ltd., Edge Lane, Droylston, Manchester M35 6UB, United Kingdom,England. If you are aware of alternative suppliers, please proved this information toASTM Headquarters. Your comments will receive careful consideration at a meetingof the responsible technical committtee,1which you may attend.
4 The sole source of supply of suitable replica tape, Press-O-Film, known to thecommittee at this time is Testex. 8 Fox Lane, Newark, DE 19711. If you are awareof alternative suppliers, please proved this information to ASTM Headquarters. Yourcomments will receive careful consideration at a meeting of the responsibletechnical committtee,1which you may attend
1
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
loose surface interference material, dirt, dust, and abrasiveresidue.
6. Procedure
6.1 Method A:6.1.1 Select the comparator standard appropriate for the
abrasive used for blast cleaning.6.1.2 Place the comparator standard directly on the surface
to be measured and compare the roughness of the preparedsurface with the roughness on the comparator segments. Thiscan be done with the unaided eye, under 5 to 10 powermagnification, or by touch. When using magnification, themagnifier should be brought into intimate contact with thestandard, and the depth of focus must be sufficient for thestandard and surface to be in focus simultaneously.
6.1.3 Select the comparator segment that most closelyapproximates the roughness of the surface being evaluated or,if necessary, the two segments to which it is intermediate.
6.1.4 Evaluate the roughness at a sufficient number oflocations to characterize the surface as specified or agreed uponbetween the interested parties. Report the range of results fromall locations as the surface profile.
6.2 Method B:6.2.1 Prior to use set the gage to zero by placing it on a piece
of plate float glass. Hold the gage by its base and press firmlyagainst the glass. Adjust the instrument to zero.
6.2.2 To take readings, hold the gage firmly against theprepared substrate. Do not drag the instrument across thesurface between readings, or the spring-loaded tip may becomerounded leading to false readings.
6.2.3 Measure the profile at a sufficient number of locationsto characterize the surface, as specified or agreed upon betweenthe interested parties. At each location make ten readings anddetermine the mean. Then determine the mean for all thelocations and report it as the profile of the surface.
6.3 Method C:6.3.1 Select the correct tape range for the profile to be
measured: coarse, 0 to 50 µm (0 to 2 mils) and extra coarse, 40to 115 µm (1.5 to 4.5 mils).
6.3.2 Remove the wax paper backing and place the tape onthe prepared surface with the foam side down, that is, put thedull side down.
6.3.3 Hold the tape firmly on the surface and rub the circularcut-out portion (approximately 6.5 mm (3⁄8 in.) diameter) withthe burnishing tool until a uniform gray color appears.
6.3.4 Remove the tape and place it between the anvils of aspring-loaded micrometer. Measure the thickness of the tape(compressed foam and non-compressible plastic film com-bined). Subtract the thickness of the noncompressible plasticfilm to obtain the surface profile.
6.3.5 Measure the profile at a sufficient number of locationsto characterize the surface, as specified or agreed upon betweenthe interested parties. At each location make three readings anddetermine the mean. Then determine the mean for all thelocations and report it as the profile of the surface.
7. Report
7.1 Report the range and the appropriate average (mean ormode) of the determinations, the number of locations mea-
sured, and the approximate total area covered.
8. Precision and Bias
8.1 Test Method A:8.1.1 Applicability—Based on measurements of profiles on
surfaces of 8 steel panels, each blast cleaned with 1 of 8different abrasives to a white metal degree of cleaning, havingknown ratings of profile height ranging from 37 µm (1.5 mils)to 135 µm (5.4 mils), the correlation coefficient for TestMethod A was found to be 0.75 and the coefficient ofdetermination was found to be 0.54.
8.1.2 Precision—In an interlaboratory study of Test MethodA in which 2 operators each running 2 tests on separate days ineach of 6 laboratories tested 8 surfaces with a broad range ofprofile characteristics and levels, the intralaboratory coefficientof variation was found to be 20 % with 141 df and theinterlaboratory coefficient was found to be 19 % with 40 df,after rejecting 3 results for one time because the range betweenrepeats differed significantly from all other ranges. Based onthese coefficients, the following criteria should be used forjudging, at the 95 % confidence level, the acceptability ofresults:
8.1.2.1 Repeatability—Two results, each the mean of fourreplicates, obtained by the same operator should be consideredsuspect if they differ by more than 56 %.
8.1.2.2 Reproducibility—Two results, each the mean of fourreplicates, obtained by operators in different laboratoriesshould be considered suspect if they differ by more than 54 %.
8.2 Test Method B:8.2.1 Applicability—Based on measurements of profiles on
surfaces of 8 steel panels, each blast cleaned with 1 of 8different abrasives to a white metal degree of cleaning, havingknown ratings of profile height ranging from 1.5 mils (37 µm)to 5.4 mils (135 µm), the correlation coefficient for TestMethod B was found to be 0.99 and the coefficient ofdetermination was found to be 0.93.
8.2.2 Precision—In an interlaboratory study of Test MethodB in which 2 operators, each running 2 tests on separate days,in each of 5 laboratories tested 8 surfaces with a broad range ofprofile characteristics and levels, the intralaboratory coefficientof variation was found to be 19 % with 113 df and theinterlaboratory coefficient was found to be 28 % with 32 df,after rejecting 3 results for one time because the range betweenrepeats differed significantly from all other ranges. Based onthese coefficients, the following criteria should be used forjudging, at the 95 % confidence level, the acceptability ofresults:
8.2.2.1 Repeatability—Two results, each the mean of fourreplicates, obtained by the same operator should be consideredsuspect if they differ by more than 54 %.
8.2.2.2 Reproducibility—Two results, each the mean of fourreplicates, obtained by operators in different laboratoriesshould be considered suspect if they differ by more than 79 %.
8.3 Method C (X-Coarse Tape):8.3.1 Applicability—Based on measurements of profiles on
surfaces of 8 steel panels, each blast cleaned with 1 of 8different abrasives to a white metal degree of cleaning, havingknown ratings of profile height ranging from 37 µm (1.5 mils)to 135 µm (5.4 mils), the correlation coefficient for Test
D 4417
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Method C (X-Coarse Tape) was found to be 0.96 and thecoefficient of determination was found to be 0.93.
8.3.2 Precision—In an interlaboratory study of Test MethodC (X-Coarse Tape) in which 2 operators each running 2 tests onseparate days in each of 6 laboratories tested 8 surfaces with abroad range of profile characteristics and levels, the intralabo-ratory coefficient of variation was found to be 9 % with 120 dfand the interlaboratory coefficient 13 % with 32 df. Based onthese coefficients, the following criteria should be used forjudging, at the 95 % confidence level, the acceptability ofresults:
8.3.2.1 Repeatability—Two results, each the mean of fourreplicates, obtained by the same operator should be consideredsuspect if they differ by more than 25 %.
8.3.2.2 Reproducibility—Two results, each the mean of fourreplicates, obtained by operators in different laboratoriesshould be considered suspect if they differ by more than 37 %.
8.4 Test Method C (Coarse Tape):8.4.1 Applicability—Based on measurements of profiles on
surfaces of 6 steel panels, each blast cleaned with 1 of 6different abrasives to a white metal degree of cleaning, havingknown ratings of profile height ranging from 37 µm (1.5 mils) to 57 µm (2.3 mils), the correlation coefficient for TestMethod C (Coarse Tape) was found to be 0.48 and thecoefficient of determination was found to be 0.23.
8.4.2 Precision—In an interlaboratory study of Test MethodC (Coarse Tape) in which 2 operators each running 2 tests onseparate days in each of 5 laboratories tested 6 surfaces with abroad range of profile characteristics and levels, the intralabo-ratory coefficient of variation was found to be 11 % with 90 df
and the interlaboratory coefficient 11 % with 24 df. Based onthese coefficients, the following criteria should be used forjudging, at the 95 % confidence level, the acceptability ofresults:
8.4.2.1 Repeatability—Two results, each the mean of fourreplicates, obtained by the same operator should be consideredsuspect if they differ by more than 30 %.
8.4.2.2 Reproducibility—Two results, each the mean of fourreplicates, obtained by operators in different laboratoriesshould be considered suspect if they differ by more than 28 %.
8.5 Bias—Since there is no accepted reference materialsuitable for determining the bias for the procedure in these testmethods for measuring surface profile, bias cannot be deter-mined.
NOTE 2—The test methods measure different values and the qualitativerating on which the applicability was determined also measures a differentvalue. The mode is determined with the comparator of Test Method A. Theheight of a single valley below a plane at the level of the highestsurrounding peaks is measured with the fine pointed probe of Test MethodB. The distance from the bottoms of many of the deepest valleys to thetops of the highest peaks (maximum profiles) are measured with thecomposite plastic of Test Method C. The height of a single peak above anadjacent valley below is measured with a microscope for the qualitativerating that is compared with each of the methods in correlation calcula-tions. Because the results for the microscope and for the fine pointed probeare measurements to an individual valley, the readings range over muchbroader limits than the results of the tape or the comparator.
9. Keywords
9.1 abrasive; abrasive blast cleaning; anchor pattern; surfaceprofile; surface roughness
The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connectionwith any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any suchpatent rights, and the risk of infringement of such rights, are entirely their own responsibility.
This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make yourviews known to the ASTM Committee on Standards, at the address shown below.
This standard is copyrighted by ASTM, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above address or at610-832-9585 (phone), 610-832-9555 (fax), or [email protected] (e-mail); or through the ASTM website (www.astm.org).
D 4417
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1. Scope
1.1 This Guide describes the most commonly used fi eld methods for the retrieval and analysis of soluble salts on steel and other nonporous substrates. Laboratory methods are only included for situations where laboratory control is desired. Much of this information was contained in SSPC-TU 4, Field Methods for the Retrieval and Analysis of Soluble Salts on Substrates, which will be withdrawn after publication of this Guide.1
2. Description and Use
2.1 Coatings applied on surfaces contaminated with soluble salts exceeding a certain concentration exhibit dimin-ished performance. This Guide is intended to assist the user in selecting specifi c procedures for retrieving and analyzing soluble salts. Section 4 of the Guide discusses the various methods for retrieving salts from a surface. Section 5 discusses the analytical methods used to determine the concentration of the soluble salts in the extracted solution. See Appendix E for links to information on sources for testing equipment and materials.
3. Referenced Standards
3.1 SSPC STANDARDS AND JOINT STANDARDS:1
SP 5/NACE No. 1 White Metal Blast Cleaning 3.2 INTERNATIONAL ORGANIZATION FOR STAN-
DARDIZATION (ISO) STANDARDS:2
ISO 8502 Preparation of steel substrates before application of paints and related products - Tests for the as-sessment of surface cleanliness
Part 2 Laboratory determination of chlo-ride on cleaned surfaces (ISO 8502-2:1992)
Part 5 Measurement of chloride on steel surfaces prepared for painting– Ion
detection tube method (ISO 8502-5:1998)
Part 6 Extraction of soluble contaminants for analysis–The Bresle method (ISO 8502-6:1995)
Part 9 Field method for conductimetric determination of water-soluble salts (ISO 8502-9:1998)
Part 10: Field method for the titrimetric determination of water-soluble chloride (ISO 8502-10:1999)
Part 12: Field method for the titrimetric determination of water-soluble ferrous ions (ISO 8502-12:2003)
4. Retrieval Methods
4.1 CLASSES OF RETRIEVAL METHODS: Salt retrieval methods employed to help determine surface concentrations of salt on substrates fall into three general classes, which can be further subdivided. (See Appendix E for links to information on testing equipment and materials.)
4.1.1 Class A: Class A retrieval involves a methodology for containing a liquid that is held in contact with a surface of predetermined area. Turbulence within the contacting liquid enhances the dissolution of the salt contamination into the solution.
Method A1: Patch Cell Retrieval Method: This method utilizes a small adhesive patch covered with a latex fi lm, which attaches to the structure forming a cell cavity. Self-contained adhesive edges allow the cell to adhere to the surface. Distilled or deionized water or a proprietary extraction liquid is then injected into its center with a hypodermic needle. The patch fi lls up like a large paint blister. The liquid is massaged against the surface being tested, retrieved from the patch using the hypodermic needle, and tested for concentration of ions.
Method A2:Sleeve Retrieval Method: This method uses a small fl exible chloride-free latex sleeve (sock) with a self-contained adhesive edge that is attached to the structure being
SSPC: The Society for Protective Coatings
TECHNOLOGY GUIDE 15
Field Methods for Retrieval and Analysis of Soluble Salts on Steel and Other Nonporous Substrates
1 Single copies of withdrawn standards may be obtained from SSPC upon request.2 International Organization for Standardization (ISO), Case Postale 56, Geneva CH-1211, Switzerland. ISO standards may be obtained
through the American National Standards Institute, 1819 L Street, NW, Suite 600, Washington, DC 20036 (www.ansi.org).
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SSPC-Guide 15June 1, 2005
tested, forming a cavity. A salt retrieval solution is dosed into the sleeve prior to attachment. The solution is massaged against the surface being tested for a specifi ed period of time and is then removed. The sleeve then is removed and the solution tested for levels of chloride and/or nitrate. A kit is available for this method, with operating instructions and a pre-measured (fi xed volume) proprietary solution.
4.1.2 Class B: Class B retrieval involves a methodology for containing a known volume of liquid within a measured area that is in contact with the surface. There may or may not be mechanical rubbing of the surface.
Method B1: Swabbing or Washing Methods: A low conductivity liquid such as deionized water and cotton swabs are used to extract salts from a surface. The method requires that the operator wear non-chlorinated latex rubber gloves to prevent cross contamination of the surface or the retrieved sample by salts naturally present on the surface of the skin. After swabbing the surface, the liquid is tested for concentra-tion of ions.
Method B2: Filter Paper Extraction Method: A pre-wet-ted absorbent fi lter paper is placed on the surface from which the salt is to be extracted. The paper wets the surface and extracts soluble salts. After a pre-determined time, the paper is removed from the surface and placed over the electrodes of a resistivity meter. The meter indicates the conductivity of the wetted paper. The conductivity is proportional to the total dissolved salts.
4.1.3 Class C: Class C retrieval is used only in a labora-tory setting and involves immersing the entire surface in boiling water. This method uses a predetermined volume of extraction liquid and a predetermined surface area.
Method C: Boiling Extraction Method: This method involves the use of boiling deionized water to extract salts from a sample coupon. This method is intended to be used for the extraction of salts from sample substrates in a laboratory setting. It may be used as a reference method to derive retrieval rates for the patch cell, sleeve, swabbing, and fi lter paper extraction methods described above. It may also be used for fi eld samples cut from a structure or test panels exposed in a fi eld or lot or cabinet. This method is described in Appendix A.
4.1.4 The fi rst four methods can be used to help character-ize surfaces encountered in either laboratory or fi eld settings. In general, boiling extraction methods are only useful under laboratory conditions. No fi eld or laboratory method is believed capable of retrieving all the soluble salt from a surface. The proportion of salt retrieved by fi eld methods depends on the method used, the roughness of the examined surface, the degree of rusting, and the ambient conditions. The presence of pits or deep craters on the surface can lead to grossly inac-
curate measurement of salt contamination, because salts in the bottoms of deep pits may escape detection.
4.2 EXTRACT SOLUTION: All the retrieval procedures described in this document use deionized or distilled water (designated as reagent water) or a proprietary solution.
4.2.1 Reagent Water: Reagent water used for salt retrieval should have a maximum conductivity of 5 microsiemens per centimeter (µS/cm). Distilled water may be purchased at gro-cery stores but verifi cation of the conductivity is recommended. Alternatively, a portable demineralizer may be used to make deionized water on site. Pour tap water into the plastic bottle, attach the demineralizer cartridge in the direction indicated, invert, and squeeze out the desired amount of water (for many of the tests described below, at least 25 mL will be required). The cartridge can be used until the blue color turns brown, as indicated on the side of the cartridge. Once this occurs, replace the cartridge. Each cartridge should deionize approximately 3000 mL of water.
4.2.2 Proprietary Solutions: Proprietary solutions may be included with commercial extraction kits. These solutions should only be used for the soluble salts described in the kit instructions. Proprietary solutions are not normally suitable for measuring conductivity of extracted solutions.
4.3 PATCH CELL RETRIEVAL METHOD: The patch cell sampling procedure is described in detail in ISO 8502-6.
4.3.1 Sample Acquisition Procedure1. Remove the backing and the foam insert from the test
cell and apply the cell fi rmly and tightly to a dry test surface. All orientations, including vertical, horizontal, or overhead are acceptable.
2. Insert the needle attached to the 5 mL syringe into the cell through its spongy foam perimeter, taking care not to inject beneath the foam or into the latex fi lm. Evacuate the air from the test area by pulling back on the plunger. Expel the air from the syringe. Fill the syringe with 3 mL of the extraction liquid.
3. Inject 3 mL or other designated quantity of extraction liquid into the above cell taking care to keep air bubbles out of the syringe. Hold the cell perimeter fi rmly during this operation to prevent water leakage.
4. Remove the needle from the cell center (but not the spongy foam perimeter) and gently rub the top of the cell for 10 to 15 seconds to encourage dissolution of soluble salts. Increasing the massage time may increase the effi ciency of the extraction liquid.
5. Withdraw and re-inject the extraction liquid a minimum of three times, each time gently rubbing the top of the cell for 10 to 15 seconds. Then, remove as much of the extraction liquid as possible and place it in a clean vial or other container. A new clean container should be
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SSPC-Guide 15June 1, 2005
used for each test, or if reused, the container should be rinsed two or more times with reagent water.
6. If additional testing requires a higher volume of extraction liquid than that afforded by the extraction procedure, add extraction liquid to raise the sample volume to the required level and note the new sample volume and dilution percentage.
7. Use the extraction liquid from step 6 to determine chloride ion concentration, ferrous ion concentration, or other ion concentrations using one of the methods described in Section 5 (see Section 4.2.2).
8. If additional samples are to be taken, always use a fresh cell and clean syringe and needle; this will avoid cross contamination between samples.
4.3.2 Advantages of the Patch Cell Method: 1. The adhesively attached cells can conform to curved
and irregular surfaces. 2. Cells such as these are commercially available in
a variety of sizes; the most commonly used size retrieves salt from a surface of 12.5 cm2. Smaller cell sizes permit assays of salt levels to be made at local corrosion sites such as craters or pits.
3. If reagent water has been used as the extraction liquid, conductivity can be determined using commercially available conductivity meters.
4. Acidic extraction liquids (such as the one furnished in the proprietary kit for this procedure) normally provide better extraction effi ciency than deionized water.
4.3.3 Limitations of the Patch Cell Method:1. The adhesively attached cells only accommodate a
small amount of retrieval liquid. With the most com-monly used cell size (12.5 cm2 surface area), the actual quantity of cell liquid contacting the surface is 3 mL. This can limit the range of analyses that can be performed.
2. No in-line determination of conductivity can be per-formed with these cells.
3. The cell may not adhere well to rusted surfaces, but it may adhere so well to abrasive blast cleaned surfaces that it is diffi cult to remove.
4. The cell may leak through the hole introduced by the syringe.
5. The cells are consumable and can be used only once.
4.3.4 Retrieval Effi ciency: see Appendix D.
4.4 SLEEVE RETRIEVAL METHOD
4.4.1 Sample Acquisition Procedure1. Remove the cap from the bottle of premeasured extract
and pour the entire contents into the sleeve.
2. Remove the pressure sensitive backing from the sleeve adhesive ring.
3. Remove most of the air from within the sleeve by squeezing the sleeve between fi ngers and thumb. Do not spill any extraction solution from the sleeve when evacuating air.
4. Firmly apply the sleeve to the test surface. Lift and hold the free end of sleeve upright to allow the extraction liquid to come into contact with the surface
5. Use the other hand to massage the solution through the sleeve against the surface for 2 minutes. It should be noted that increasing the massage time (e.g., up to 6 minutes) will increase the extent of salt removal. When the massage is complete, remove the sleeve and solution from the surface. For vertical or overhead surfaces, the extract solution will return to the lowered area in test sleeve. For horizontal surfaces press and slide a fi nger across the sleeve to move the solution to the closed end of the sleeve prior to removal.
4.4.2 Advantages of the Sleeve Retrieval Method: 1. This method is very simple to perform, as all compo-
nents are pre-measured.2. The adhesive sleeve can conform to curved and ir-
regular surfaces. Tests can be performed on vertical, horizontal, and overhead surfaces.
3. For extremely rough or pitted surfaces, the seal ring may be doubled, thereby allowing testing to be per-formed.
4. The kit form of this method provides a pre-measured volume of extraction solution and a fi xed area of the sleeve opening. These features are designed to pro-vide a direct fi nal reading in micrograms per square centimeter (µg/cm2).
5. All components are one-time usage, eliminating cross contamination from test to test.
6. In hot weather or on hot surfaces, the encapsulated extract solution will not evaporate.
7. The extractions also provide suffi cient sample size for analyses to be performed for different ions.
8. Acidic extraction liquids (such as the one furnished in the proprietary kit for this procedure) normally provide better extraction effi ciency than deionized water.
4.4.3 Limitations of the Sleeve Retrieval Method:1. The adhesive sleeve may not adhere well to rusted
surfaces, but it may adhere so well to abrasive blast cleaned surfaces that it is diffi cult to remove.
3. No in-line conductivity testing can be performed with the sleeves.
4. The sleeves are consumable and can be used only once.
4.4.4 Retrieval Effi ciency: see Appendix D.
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SSPC-Guide 15June 1, 2005
4.5 SWABBING OR WASHING METHOD
The materials, procedures, and advantages and limi-tations are described below. A similar procedure is described in ISO 8502-2, Sections 5 and 6.
4.5.1 Procedure for Swabbing Method:1. Use a ruler and chloride free marker to outline a
representative surface area of specifi c size (e.g., 15 by 15 cm [6 by 6 inch]).
2. From a graduated cylinder, pour a measured volume (e.g., 22.5 mL) of reagent water into one of two plastic beakers (beaker A.) (Note: The suggested sample volume and area computes to 1 mL per 10 cm2. This can simplify later calculations of salt contamination levels.)
3. Repeat step 2 with the second beaker (beaker B).4. Using a pair of tweezers or chloride free latex or rubber
gloves, dampen a sterile cotton ball or chloride free small sponge in the water in beaker A. Thoroughly swab the area measured in step 1, taking care to avoid dripping the liquid on the surface. After swab-bing, swirl the applicator (cotton ball or sponge) in the water and then squeeze it against the inside of beaker A to extract as much water as possible from the applicator.
5. Repeat this swabbing, swirling, and squeezing opera-tion four times with fresh applicators and then leave the applicators in the water in beaker A.
6. Use an applicator to dry the measured test area and place it in beaker A.
7. Stir the water and applicators for two minutes to achieve thorough mixing and to extract salts from the cotton swabs or sponge.
8. Record the fi nal volume. 9. Take the same number of fresh applicators, identical to
those used in steps 4 through 7 above, and immerse them in beaker B. Then stir as in Steps 4 and 5, and let sit, covered, for at least three minutes. This will provide the control sample.
4.5.2 Retrieval Effi ciency: see Appendix D:
4.5.3 Advantages of Swabbing Method: 1. The swabbing retrieval method provides a means
for acquiring samples of salt from steel or other non-porous surfaces using readily available materials.
2. Retrievals can be conducted on a range of surfaces without regard to surface irregularities or condition.
3. The swabbing method can be used on large areas to indicate general surface contamination by salts.
4. The extractions also provide suffi cient sample size for several analyses to be performed for different ions.
4.5.4 Limitations of Swabbing Method: 1. Swabbing methods are diffi cult to perform in an
overhead or vertical position. Extracted liquid may be lost dripping from the swabs.
2. Swabbing is not well suited for measuring salt levels of small, localized contamination such as craters or pits.
3. There is a risk of contamination of a sample by the operator if gloves or any other equipment used for these procedures become damaged.
4. In hot weather or on hot surfaces the extraction liquid may evaporate on the surface prior to its removal.
4.6 FILTER PAPER EXTRACTION METHOD
4.6.1 Sample Acquisition Procedure:
1. Put on a pair of clean chloride free latex or rubber gloves.
2. Fill a syringe with the specifi ed level (about 2 mL) of reagent water (see Section 4.2.1).
3. Eject the water from the syringe onto the paper surface taking care to retain as much water as possible on the paper. Note: Use only sample paper recommended by the manufacturer as soluble salt free. Commercial fi lter papers are not suitable as they can contain excessive salt levels.
4. Place the wetted paper on the area to be sampled, pressing it fi rmly into its contours and surface irregu-larities.
5. Press out as much entrapped air as possible from beneath the paper.
6. When 2 minutes have elapsed, remove the sample paper from the surface for analysis.
Refer to Section 5.3 for analysis procedure.
4.6.2 Advantage of Filter Paper Extraction Method:The fi lter paper procedure is relatively simple and is less subject to operator error.
4.6.3 Limitations of Filter Paper Extraction Method:
1. The instrument measures total soluble salts, rather than a specifi c ion such as chloride or nitrate.
2. There is no independent data on the accuracy or precision of this method.
3. The water is subject to evaporation loss under condi-tions of high temperature and/or low humidity.
5. Analytical Methods
5.1 QUANTITATIVE ANALYSIS: This section discusses the most common analytical methods used to determine the amount of soluble salt contamination in the extracted solution.
5
SSPC-Guide 15June 1, 2005
The following substances and quantities are described:• Conductivity• Soluble Chloride Ion• Soluble Ferrous Ion • Soluble Sulfate Ion• Soluble Nitrate Ion
5.1.1 Precision and Accuracy of Quantitative Measure-ments: In response to requests from SSPC, some suppliers of proprietary equipment have provided data on precision and accuracy of analytical methods. If this information was provided, it is given in the section describing the method. Information provided by suppliers has not been verifi ed by third-party test-ing. Users are advised to contact the manufacturers directly to obtain additional information that is not provided in the guide. See Appendix E for links to equipment suppliers and manufacturers.
5.2 FIELD MEASUREMENT OF CONDUCTIVITY (TOTAL SOLUBLE SALTS)
5.2.1 This method provides a measurement of solution conductivity. Conductivity is a measure of the total dissolved salts.
5.2.2 Types of conductivity meters: Commercially avail-able portable conductivity meters available include “pocket” type, “cup” type, and meters with specifi c features. The “pocket” types are operated by placing the probe into the liquid to be analyzed. For the “cup” type, the liquid is placed in a cup that forms part of the meter. One special meter is that described in Section 5.3 for analyzing the fi lter paper. Each meter has its own degree of accuracy.
5.2.3 Test Procedure
5.2.3.1 Procedure for pocket-type conductivity meters: This procedure entails two measurements: the fi rst of the control solution (typically reagent water), which is Reading One, and the second of the extraction liquid, which is Reading Two. Wash the probe end of conductivity meter with reagent water prior to each reading to prevent cross contamination. Place the probe end of a calibrated conductivity meter into the reagent water and record the reading on the meter (Reading One). Then repeat the procedure for the extracted liquid (Reading Two). Subtract Reading One from Reading Two. The resulting number is the corrected conductivity of the extracted liquid.
5.2.3.2 Procedure for cup-type conductivity meters: If an external cup conductivity meter is used, transfer about 10 milliliters of the reagent water into the cup of the calibrated conductivity meter. Select the appropriate range and record the conductivity reading in µS/cm (Reading One). Transfer some of the extracted liquid into the cup and record conductivity (Reading Two).
Subtract Reading One from ReadingTwo. The resulting number is the corrected conductivity of the extracted liquid. A similar method is also described in ISO 8502-9.
See Appendix C for a procedure to estimate equivalent chlo-ride ion surface concentrations from conductivity of extract.
5.3 FIELD PROCEDURE FOR ANALYZING FILTER PAPER FOR SOLUBLE SALTS: Place the sample paper over the concentric copper electrodes of the resistivity meter, ensuring that the outer ring is completely covered. All air must be excluded from beneath the paper. The lid is closed, and after seconds, the reading is displayed in µg/cm2, based on sodium chloride. The manufacturer of one device has prepared charts showing the variation in the salt level readings due to simulated marine and simulated urban salt concentrations and due to temperature.
5.4 FIELD DETECTION OF CHLORIDE ION BY ION DETECTION TUBE: This method uses sealed vacuum tubes with crystals impregnated with silver dichromate (pink). The ends of the tubes are snapped off, opening the tube much like a straw. When one end of the tube is immersed in the extract solution, capillary action wicks the solution to the top of the tube. On contact with the chloride ion the silver dichromate converts to silver chloride (white). When the solution reaches the top of the tube, the white cotton at the top changes color to amber. This indicates the titration is complete. Graduations on the side of the tube provide the level of chloride ions pres-ent in the solution. This method, described in ISO 8502-5, can detect chloride levels from 1 to 2000 ppm, using tubes with varying ranges of detection. The tube most commonly used for surface testing of chlorides has a detection range of +0 to 60 ppm. One supplier provided the following data on standard deviation (sd) at different concentrations (C): C of 1.0 ppm, sd of 0.38 ppm; C of 3.0 ppm, sd of 0.17 ppm; C of 5.0 ppm, sd of 0.30 ppm; C of 10 ppm, sd of 0.48 ppm; C of 30 ppm, sd of 0.50 ppm. See Appendix B for information on converting from a solution concentration in ppm to a surface concentration in µg/cm2.
5.5 FIELD DETECTION OF CHLORIDE ION BY PAPER STRIP METHOD: To determine the chloride level, place the lower end of a test strip into the extracted solution. Allow the solution to wick up and saturate the test strip, as indicated by the yellow band across the top of the strip turning blue (about 5 minutes). Then, record the scale number at the top edge of the white column (chloride ion causes the existing tan color on the strip to turn white) and compare it with the conversion chart enclosed with the test strip bottle. The range of concentration over which this method is useful is from 30 to 600+ ppm chlo-ride ion. The precision reported by one manufacturer is ± 10% chloride. Note: The reading from the strip must be converted to ppm using the supplied conversion chart corresponding to the batch of test strips used for the analysis. See Appendix B for information on converting from a solution concentration in ppm to a surface concentration in µg/cm2.
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SSPC-Guide 15June 1, 2005
5.6 FIELD DETECTION OF CHLORIDE ION BY FIELD TITRATION METHOD
5.6.1 Test Procedure: A commercially available test kit is used to analyze the solution collected from the surface. The titration (sometimes referred to as “drop titration”) is performed on a small sample (2 to 3 mL) from the extracted solution. The kit includes four solutions contained in separate reagent bottles. The procedure is as follows:
1. Using Reagent Bottle 1, press (squeeze) out 2 drops of red indicator liquid into a plastic vial containing the sample solution. Carefully agitate the liquid until it is homogeneous in color (purple).
2. Using Reagent Bottle 2, squeeze out 2 drops into the vial. The sample liquid should be yellow in color. If not, add drop-by-drop additional Reagent 2 until sample turns yellow, agitating between each drop addition.
3. At this point, a judgment should be made as to how much chloride is anticipated. If low surface con-centrations (0 to 10 µg/cm2) are expected, proceed using Reagent Bottle 4. If higher concentrations are expected, proceed using Reagent Bottle 3.
4. For low concentrations, add, drop by drop, the con-tents of Reagent Bottle 4. For high concentrations, add, drop by drop, the contents of Reagent Bottle 3. In either case, thoroughly agitate the solution after the addition of each drop. Count the number of drops required to turn the solution from yellow to blue, thor-oughly agitating the solution after the addition of each drop. The procedure is described in ISO 8502-10.
5.6.2 Determining surface concentration: Each drop from Reagent Bottle 4 is equivalent to approximately 25 µg of chloride recovered from the surface. Each drop from Reagent Bottle 3 is equivalent to approximately 125 µg of chloride recov-ered from the surface. Use the following formulas to determine the maximum surface concentration in µg/cm2 (see note below) knowing the surface area (cm2) and the number of drops.
For Reagent Bottle 4:
actual concentration may range from that computed from the preceding drop to the concentration computed from formulas 1 and 2 (e.g., for 4 drops from Reagent Bottle 4 for a solution extracted from a surface area of 12.5 cm2, the concentration range would be 6 to 8 µg/cm2). (Commonly used patch cells have a surface area of 12.5 cm2.) This method does not deter-mine a specifi c surface concentration of chloride ion, but rather the results are reported as a range, e.g., greater than 6 and less than 8 µg/cm2 chloride ion. One manufacturer reports a sampling accuracy of 1 to 2 µg/cm2 or 5 to 10 µg/cm2 depend-ing on the specifi c titration chemicals used. No information on precision was provided.
5.7 LABORATORY REFERENCE METHOD FOR DE-TECTION OF CHLORIDE ION BY TITRATION: ISO 8502-2, “Laboratory determination of chloride on cleaned surfaces,” describes a titration method based on the reaction of chloride ion with mercuric nitrate to form insoluble mercuric chloride. The indicator is a solution of diphenylcarbazole/bromophenol blue, which turns to an intense violet color to indicate the completion of the titration.
5.8 QUALITATIVE FIELD DETECTION OF FERROUS ION: In this method (described in ISO 8502-12) blotting paper is treated with potassium ferricyanide solution. The blotting paper is moistened and placed in contact with the steel surface to be tested. On contact with ferrous ions, the paper shows blue spots. The sensitivity of the method is less than 1 ppm ferrous ion. No information on precision is available, as this is a qualitative test.
Potassium ferricyanide test paper may be used as an economical screening test for active corrosion sites. It is spe-cifi c to soluble ferrous ion. When used properly, it will not give false negatives, but may produce false positives. If soluble salt concentration is suspected due to a positive indication using potassium ferricyanide paper, then confi rming tests utilizing another ion-specifi c test method may be required.
5.9 QUANTITATIVE FIELD DETECTION OF FERROUS ION: To determine the ferrous ion concentration in parts per million, moisten a ferrous ion test strip with the solution being tested and compare the resulting color to the color chart on the container label. A complex is formed between 1,10-phenanth-roline and ferrous ion that has a vivid red color. Color changes are seen even at ferrous ion concentrations below 1 ppm. Typical concentration ranges for test strips are between 0.5 and 10 ppm ferrous ion. Iron test strips from one manufacturer are graduated in unequal steps: 0-3-10-15-50-100-250-500 ppm. No data is available on the precision of this technique. See Appendix B for information on converting from a solution concentration in ppm of solution to a surface concentration in µg/cm2. Note that a proprietary kit provides the readings directly in µg/cm2.
For Reagent Bottle 3:
Note: Because it is impossible to determine whether the entire drop or a fraction of the drop was needed to turn the solution from yellow to blue, the concentrations derived from the above formulas represent the maximum concentrations. The
maximum surface concentration (µg/cm2) =
25 • (# drops)
surface area (cm2)
maximum surface concentration (µg/cm2)
= 125 • (# drops)
surface area (cm2)
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SSPC-Guide 15June 1, 2005
5.10 FIELD DETECTION OF SULFATE ION: This method works on the principle that if sulfate is present in the solution, it becomes turbid (cloudy) when barium chloride is added. The simplest instrument for measuring the degree of turbidity in the fi eld is the optical comparator. Barium chloride is avail-able as powder or pre-measured tablets. The tablets are more convenient to use but take a little longer to dissolve. Panes of plastic with a known degree of cloudiness are compared side by side with the sample prepared using the kit. The pane closest in cloudiness to that of the sample is taken as the sample sulfate level. The interval between each pane value has to be quite large, because the eye is not as discriminat-ing as a well-calibrated spectrophotometer in the laboratory. Also, because the eye is not sensitive to very low levels of turbidity, the minimum level of sulfate that can be detected by this method is around 20 ppm. No data is available on the precision of this technique. See Appendix B for information on converting from a solution concentration in ppm of solution to a surface concentration in µg/cm2.
5.11 FIELD DETECTION OF SULFATE ION BY PHOTO-ELECTRIC COLORIMETER: This proprietary method uses an electronic microprocessor, factory programmed, that measures the turbidity of a solution after barium chloride powder has been mixed with the test solution. This method is more sensi-tive than the visual method (Section 5.10). The colorimeter readings are in parts per million (ppm), and the range is from 1 to 100 ppm. The supplier reports that the accuracy of this unit over the full photometric range is ± 2%. See Appendix B for information on converting from ppm of the test solution to µg/cm2 of the surface concentration. Note: the proprietary kit provides the readings directly in µg/cm2.
5.12 FIELD DETECTION OF NITRATE ION BY PAPER STRIP: To determine the nitrate concentration, place the lower end of a test strip into the extract for two seconds. Allow the strip to stand for one minute. Observe the color and compare to the color shown on the strip. The technique measures the solution concentration in ppm. The detection range is up to 50 ppm nitrate. No data is available on the precision of this technique. See Appendix B1 for information on converting a solution concentration in ppm of solution to a surface concen-tration in µg/cm2. Note: a proprietary kit provides the readings directly in ppm.
6. Disclaimer
6.1 This guide is designed to describe, review, or analyze new or improved technology and does not meet the defi ni-tion of a standard as defi ned by SSPC. A guide differs from a standard in that it is (a) a set of instructions or organized information based on a consensus of best industry practice, and (b) a set of directions provided to aid in preparing one’s own modifi ed specifi cations.
6.2 While every precaution is taken to ensure that all in-formation furnished in SSPC guides is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials or methods described herein, or of the guide itself.
6.3 This guide does not attempt to address problems concerning safety associated with its use. The user of this guide, as well as the user of all products or practices described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all govern-mental regulations.
APPENDIX A: Boiling Extraction Method
A.1 Materials Required: This laboratory reference pro-cedure requires the following items (all apparatus and sample containers should be previously cleaned with deionized or distilled water):
1. Hot plate with thermostatic control2. Reagent water, conductivity no greater than 5 µS/cm3. Inert glass granules to prevent bumping of boiling
water. (Note: the use of boiling stones or chips is not suggested, as these contribute ions to the water and buffer the pH of the extraction liquid on the alkaline side.)
4. Steel panels of known dimensions (e.g., 10 x 15 x 0.64 cm [4 x 6 x 1/4 inch]), previously cleaned to refl ect the specifi cation level of cleanliness used in the fi eld, using the same abrasive as used in the fi eld. If a level of cleanliness is not specifi ed, then panels are cleaned to SSPC-SP 5/NACE No. 1.
5. Stainless steel or Pyrex pans of dimension no less than 15 x 20 x 5 cm (6 x 8 x 2 inch)
6. Test panels of dimensions no greater than 13 x 18 x 2.5 cm (5 x 7 x 1 inch)
7. 500 mL graduated cylinder8. Stainless steel tongs9. Conical funnel10. 750 mL laboratory storage bottle
A.2 Sample Acquisition Procedure1. Place the following items in the pan: • Approximately 350 mL of reagent water • Between 5 and 10 anti-bumping granules • A test panel (see item 4 of Section A.1).2. Place the pan on the hot plate and raise water tem-
perature to boiling over a period from 10 to 20 minutes. Maintain the temperature at boiling for 1 hour. The test panel must be kept completely submerged. If liquid is lost by boiling evaporation, it must be replenished during the test. If the panel is placed horizontally in the pan, turn the panel over after 30 minutes.
3. At the end of the test, turn off the hot plate, and remove the pan from the hot plate. Allow the liquid in the pan to cool for at least 30 minutes.
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SSPC-Guide 15June 1, 2005
4. The steel test panel may be removed from the pan with stainless steel tongs either hot or after cooling. It should be rinsed with a small quantity of reagent water to remove any soluble salt ions from the sur-face, and drained over the pan. When the panel has drained dry, remove it from the work area.
5. Using the conical funnel, transfer the liquid in the pan to the graduated cylinder. Add suffi cient reagent water to the graduated cylinder to bring the volume of material up to 500 ml.
6. Mix the total liquid thoroughly by transferring it between the storage bottle and the graduated cylinder.
A.3 Advantage of Boiling Extraction Method: This method provides a benchmark for determining the maximum retrieval effi ciency of fi eld retrieval methods.
A.4 Limitation of Boiling Extraction Method: This method is unsuited for use in the fi eld. The use of laboratory-contaminated samples may provide some indication of relative extraction effi ciencies, but because fi eld conditions responsible for salt contamination are highly variable, it is best to use actual fi eld samples where possible.
APPENDIX B: Conversions
B.1 Determining Surface Concentration from Solution Concentration: One can convert the solution concentration to an equivalent surface concentration as follows:
where:
Example:E = 10 µg/cm2
A= 12.5 cm2
V= 2 mL
C = solution concentration in ppm (µg/cm3)E = surface concentration in µg/cm2
V = volume of extract solution in mL (1 mL = 1 cm3) A= area in cm2
Example:C = 42 ppmA= 12.5 cm2
V= 2 mL
B.2 Determining Solution Concentration from Surface Concentration: One can convert the surface concentration to an equivalent solution concentration as follows:
where:C = solution concentration in ppm (µg/cm3)E = surface concentration in µg/cm2
V = volume of extract solution in mL A= area in cm2
E = surface concentration of equivalent chloride in µg/cm2
S = conductivity in µS/cmV = volume of extract solution in mLA = area in cm2
Example:S = 70 µS/cmV = 2 mLA = 12.5 cm2
* This formula is valid only where sodium chloride is the only soluble salt and at low concentrations. In actual fi eld samples, there are almost always other salts present.
B3. Unit Conversions:
1 ppm = 1 µg/cc of water1 mL = 1 cc = 1 cm3
1 µg/cm2 = 10 mg/m2
APPENDIX C: Determining Equivalent Surface Concentration From Conductivity
Note: The ability to remove all of the soluble salt ions from the surface of a structure that has been in service for extended periods of time and is severely corroded and or pitted has not yet been demonstrated. Therefore, all extraction tests remove less than 100% of the soluble salt ions from the structures, and the amount in the samples represents an unknown per-centage of the amount actually existing on the structure. The test methods that are indicated in this document are therefore semi-quantitative and do not represent the actual amount of soluble salt ions existing on the structure.
C.1 Equivalent Surface Concentration of Chloride from Conductivity of Chloride Solution:This procedure may be used when one suspects that the only (or major) soluble salt present on a surface is chloride. Assuming that all salt is pres-ent as chloride can provide a worst-case scenario, as chloride is generally agreed to be the most aggressive in accelerating corrosion and inducing osmotic blistering.
One can estimate the solution concentration from the con-ductivity if one knows or assumes the identity of the soluble salt. For example, if one assumes that the salt is sodium chloride only, the solution concentration is estimated as follows:
where:
E = 42 212.5
= 6.7 µg/cm2•
C = E • (Formula 2)VA
E = (0.3) • S • VA
(Formula 3*)
E = C • VA
(Formula 1)
C = 10 • 12.52
= 62.5 ppm
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SSPC-Guide 15June 1, 2005
C.2 Equivalent Surface Concentration of Total Salt from Conductivity: Based on measurement of the average conductivity from 12 representative samples of soluble salts, an ISO committee developed the following formula for converting conductivity to surface concentration of salts (ISO 8502-9).
Where:E1 = surface concentration of total chloride in µg/ cm2
S = conductivity in µS/cmV = volume of extract solution in mLA = area in cm2
Example:S = 70 µS/cmV = 2 mLA = 12.5 cm2
C.3 Comparison of Methods C.1 and C.2
The methods C.1 and C.2 give very similar results. Method C.1 computes the concentration (E) of the chloride ion, whereas Method C.2 computes the concentration (E1) of the chloride compound. Assuming that the salt is sodium chloride, and knowing the formula weight of sodium chloride to be 58.5 and the atomic weight of the chloride ion to be 35.5, these two concentrations are related by:
originally on that surface. The extraction effi ciency varies sig-nifi cantly among different situations. Some of the signifi cant variables are:
The method of extractionThe profi ciency of the operatorThe degree of roughness of the surfaceThe size of the area from which salt is extractedThe type and concentration of the saltThe degree of corrosion and pitting of the substrateThe extraction timeThe method of contamination (i.e., by artifi cial or natural
methods)
Several studies have been conducted to evaluate the effi ciency of extraction. For several laboratory studies, the researchers applied specifi c quantities of salts over defi ned areas to provide an average concentration as a control. In a few studies, the steel substrates were exposed to the salts (e.g., in an accelerated laboratory chamber or in atmospheric exposures). For these tests, the control concentration was determined using the total extraction method (boiling). The researchers assumed that this technique would extract 100% of the soluble salts. Some studies have questioned the validity of using artifi cially doped test panels to establish extraction effi ciency.
From a review of the published literature one concludes that there is not enough data to develop specifi c extraction effi ciencies for the various extraction procedures. A list of sources for extraction effi ciencies is given below.
Bibliography for Appendix D
Alblas, B.P. and van Londen, A.M. “The Effect of Chloride Contamination on the Corrosion of Steel Surfaces: A Literature Review,” Protective Coatings Europe (PCE), February 1997.
Appleman, B.R., Boocock, S.K., Weaver, R.E.F., and Soltz, G.C. “Effect of Surface Contaminants on Coating Life,” SSPC #91-07, Pittsburgh, PA: SSPC 1991.
Appleman, B. R. “Advances in Technology and Standards for Mitigating the Effects of Soluble Salts,” Journal of Protective Coatings and Linings (JPCL), Vol. 19, No. 5, May 2002, pp. 42-47.
Boocock, S. K. “SSPC Research on Performance Testing of Abrasives and Salt Retrieval Techniques,” JPCL, Vol.-11, No. 3, March 1994, pp. 28-44.
Chong, S-L., Yao,Y. and Rozario, M, “Intra-laboratory Assessment of Commercial Test Kits for Quantifying Chloride on Steel Surfaces,” JPCL, Vol. 20, No. 8, August 2003, pp. 43-60.
Flores, S., Simancas, J., Morcillo, M. “Methods for Sampling and Analyzing Soluble Salts on Steel Surfaces: A Com-prehensive Study,” JPCL, March 1994, pp. 76-83.
Forsgren, A., Applegren, C. “Comparison of Chloride Levels Remaining on the Steel Surface After Various Pretreatments,” in Assessing the Future of Coating
••••••••
Using the values from the numerical examples above, the similarity between methods C1 and C2 can be demon-strated.
APPENDIX D: Discussion and Sources on Extraction Effi ciency
Extraction effi ciency is defi ned as the quantity of salt re-trieved from the surface as a percentage of the total amount
E1 = (0.5) • S • VA
(Formula 4)
E1 = 0.5 • 70 • 2
12.5= 5.6 µg/cm2 of soluble salt
= 5.6E1 = (3.4) • 58.535.5
concentration ofsodium chloride = concentration
of chloride ion • formula wt. of NaClatomic wt. of CI- ion
E = 0.3 •70 • = 3.4 µg/cm2 of equivalent chloride2
12.5
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SSPC-Guide 15June 1, 2005
Work: Proceedings from PCE 2000, Genoa, Italy, March 8-10, 2000. Pittsburgh, PA: Technology Pub-lishing Company, 2000.
Mitschke, Howard “Effects of Chloride Contamination on Performance of Tank and Vessel Linings,” in SSPC: Proceedings of the SSPC 2000 Seminars, SSPC #00-15. SSPC: Pittsburgh PA, 2000.
Richards, Dennis M. “Effects of Chloride Contamination of Abrasives on the Performance of Long Life Coat-ings for Steel,” in The Proceedings of the Seminars: Application & Inspection of Protective and Marine Coatings, Coatings for Asia 99, Singapore, August 30 through September 1, 1999, SSPC: Pittsburgh, PA, 1991.
Soltz, G.C. “The Effects of Substrate Contaminants on the Life of Epoxy Coatings Submerged in Seawater.” San Diego, CA: National Shipbuilding Research Program Report, Task 3-84-2. March 1991.
Steinsmo, Unni, Axelsen, Sten B. “Assessment of Salt Contamination and Determination of Its Effect on Coating Performance,” in Achieving Cost Effective-ness in Coatings Work. The Proceedings of the PCE 98 Conference and Exhibition,The Hague, The Neth-erlands, April 1-3, 1998. Pittsburgh, PA: Technology Publishing Company, 1998
APPENDIX E: Sources of Testing Equipment and Supplies
Information on suppliers of testing and analytical equip-ment may be found in the Journal of Protective Coatings and Linings Buyer’s Guide. The following web sites also provide contact information and links to manufacturers of coating testing equipment and supplies. http://www.sspc.org/links/equip.html; http://www.paintsquare.com/bg/buying_guide_equip.cfm.
Readers may also search the World Wide Web using keywords such as analytical testing equipment, Bresle, chlo-ride ion, coating test kit, conductivity, ferrous ion, ion detection tube, inspection, laboratory testing supplies, nitrate ion, paint testing equipment, and sulfate ion.
Designation: D 4541 – 02
Standard Test Method forPull-Off Strength of Coatings Using Portable AdhesionTesters 1
This standard is issued under the fixed designation D 4541; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers a procedure for evaluating thepull-off strength (commonly referred to as adhesion) of acoating on rigid substrates such as metal, concrete or wood.The test determines either the greatest perpendicular force (intension) that a surface area can bear before a plug of materialis detached, or whether the surface remains intact at a pre-scribed force (pass/fail). Failure will occur along the weakestplane within the system comprised of the test fixture, adhesive,coating system, and substrate, and will be exposed by thefracture surface. This test method maximizes tensile stress ascompared to the shear stress applied by other methods, such asscratch or knife adhesion, and results may not be comparable.
1.2 Pull-off strength measurements depend upon both ma-terial and instrumental parameters. Results obtained by eachtest method may give different results. Results should only beassessed for each test method and not be compared with otherinstruments. There are five instrument types, identified as TestMethods A-E. It is imperative to identify the test method usedwhen reporting results.
1.3 This test method uses a class of apparatus known asportable pull-off adhesion testers.2 They are capable of apply-ing a concentric load and counter load to a single surface sothat coatings can be tested even though only one side isaccessible. Measurements are limited by the strength of adhe-sion bonds between the loading fixture and the specimensurface or the cohesive strengths of the adhesive, coatinglayers, and substrate.
1.4 This test can be destructive and spot repairs may benecessary.
1.5 The values stated in MPa (inch-pound) units are to beregarded as the standard. The values given in parentheses arefor information only.
1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:D 2651 Guide for Preparation of Metal Surfaces for Adhe-
sive Bonding3
D 3933 Guide for Preparation of Aluminum Surfaces forStructural Adhesives Bonding (Phosphoric Acid Anodiz-ing)3
D 3980 Practice for Interlaboratory Testing of Paint andRelated Materials4
2.2 ANSI Standard:N512 Protective Coatings (Paints) for the Nuclear Industry5
2.3 ISO Standard:4624 Paints and Varnish—Pull-Off Test for Adhesion5
3. Summary of Test Method
3.1 The general pull-off test is performed by securing aloading fixture (dolly, stud) normal (perpendicular) to thesurface of the coating with an adhesive. After the adhesive iscured, a testing apparatus is attached to the loading fixture andaligned to apply tension normal to the test surface. The forceapplied to the loading fixture is then gradually increased andmonitored until either a plug of material is detached, or aspecified value is reached. When a plug of material is detached,the exposed surface represents the plane of limiting strengthwithin the system. The nature of the failure is qualified inaccordance with the percent of adhesive and cohesive failures,and the actual interfaces and layers involved. The pull-offstrength is computed based on the maximum indicated load,the instrument calibration data, and the original surface areastressed. Pull-off strength results obtained using different1 This test method is under the jurisdiction of ASTM Committee D01 on Paint
and Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.
Current edition approved Feb. 10, 2002. Published April 2002. Originallypublished as D 4541 – 93. Last previous edition D 4541 – 95{1.
2 The term adhesion tester may be somewhat of a misnomer, but its adoption bytwo manufacturers and at least two patents indicates continued usage.
3 Annual Book of ASTM Standards, Vol 15.06.4 Annual Book of ASTM Standards, Vol 06.01.5 Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
1
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
devices may be different because the results depend oninstrumental parameters (see Appendix X1).
4. Significance and Use
4.1 The pull-off strength of a coating is an importantperformance property that has been used in specifications. Thistest method serves as a means for uniformly preparing andtesting coated surfaces, and evaluating and reporting theresults. This test method is applicable to any portable apparatusmeeting the basic requirements for determining the pull-offstrength of a coating.
4.2 Variations in results obtained using different devices ordifferent substrates with the same coating are possible (seeAppendix X1). Therefore, it is recommended that the type ofapparatus and the substrate be mutually agreed upon betweenthe interested parties.
4.3 The purchaser or specifier shall designate a specific testmethod, that is, A, B, C, D or E, when calling out this standard.
5. Apparatus
5.1 Adhesion Tester, commercially available, or comparableapparatus specific examples of which are listed in AnnexA1-Annex A5.
5.1.1 Loading Fixtures, having a flat surface on one end thatcan be adhered to the coating and a means of attachment to thetester on the other end.
5.1.2 Detaching Assembly(adhesion tester), having a cen-tral grip for engaging the fixture.
5.1.3 Base, on the detaching assembly, or an annular bearingring if needed for uniformly pressing against the coatingsurface around the fixture either directly, or by way of anintermediate bearing ring. A means of aligning the base isneeded so that the resultant force is normal to the surface.
5.1.4 Means of moving the grip away from the base in assmooth and continuous a manner as possible so that a torsionfree, co-axial (opposing pull of the grip and push of the basealong the same axis) force results between them.
5.1.5 Timer, or means of limiting the rate of stress to lessthan 1 MPa/s (150 psi/s) so that the maximum stress is obtainedin less than about 100 s. A timer is the minimum equipmentwhen used by the operator along with the force indicator in5.1.6.
NOTE 1—Obtaining the maximum stress in 100 s or less by keeping themaximum rate of shear to less than 1 MPa/s (150 psi/s) is valid for thelevels of pull-off strength measured with these types of apparatuses.
5.1.6 Force Indicator and Calibration Information, fordetermining the actual force delivered to the loading fixture.
5.2 Solvent, or other means for cleaning the loading fixturesurface. Finger prints, moisture, and oxides tend to be theprimary contaminants.
5.3 Fine Sandpaper, or other means of cleaning the coatingthat will not alter its integrity by chemical or solvent attack. Ifany light sanding is anticipated, choose only a very fine gradeabrasive (400 grit or finer) that will not introduce flaws or leavea residue.
5.4 Adhesive, for securing the fixture to the coating that doesnot affect the coating properties. Two component epoxies6 andacrylics7 have been found to be the most versatile.
5.5 Magnetic or Mechanical Clamps, if needed, for holdingthe fixture in place while the adhesive cures.
5.6 Cotton Swabs, or other means for removing excessadhesive and defining the adhered area. Any method forremoving excess adhesive that damages the surface, such asscoring (see 6.7), must generally be avoided since inducedsurface flaws may cause premature failure of the coating.
5.7 Circular Hole Cutter (optional), to score through to thesubstrate around the loading fixture.
6. Test Preparation
6.1 The method for selecting the coating sites to be preparedfor testing depends upon the objectives of the test andagreements between the contracting parties. There are, how-ever, a few physical restrictions imposed by the general methodand apparatus. The following requirements apply to all sites:
6.1.1 The selected test area must be a flat surface largeenough to accommodate the specified number of replicate tests.The surface may have any orientation with reference togravitational pull. Each test site must be separated by at leastthe distance needed to accommodate the detaching apparatus.The size of a test site is essentially that of the secured loadingfixture. At least three replications are usually required in orderto statistically characterize the test area.
6.1.2 The selected test areas must also have enough perpen-dicular and radial clearance to accommodate the apparatus, beflat enough to permit alignment, and be rigid enough to supportthe counter force. It should be noted that measurements closeto an edge may not be representative of the coating as a whole.
6.2 Since the rigidity of the substrate affects pull-offstrength results and is not a controllable test variable in fieldmeasurements, some knowledge of the substrate thickness andcomposition should be reported for subsequent analysis orlaboratory comparisons. For example, steel substrate of lessthan 3.2 mm (1⁄8-in.) thickness usually reduce pull-off strengthresults compared to 6.4 mm (1⁄4-in.) thick steel substrates.
6.3 Subject to the requirements of 6.1, select representativetest areas and clean the surfaces in a manner that will not affectintegrity of the coating or leave a residue. Surface abrasionmay introduce flaws and should generally be avoided. A fineabrasive (see 5.3) should only be used if needed to removeloose or weakly adhered surface contaminants.
6.4 Clean the loading fixture surface as indicated by theapparatus manufacturer. Failures at the fixture-adhesive inter-face can often be avoided by treating the fixture surfaces inaccordance with an appropriate ASTM standard practice forpreparing metal surfaces for adhesive bonding.
6 Araldite Adhesive, available from Ciba-Geigy Plastics, Duxford, Cambridge,CB2 4QA, England, Hysol Epoxy Patch Kit 907, available from Hysol Div., TheDexter Corp., Willow Pass Rd., Pittsburg, CA 94565, and Scotch Weld Adhesive1838B/A, available from 3M, Adhesives, Coatings and Sealers Div., 3M Center, St.Paul, MN 55144, have been found satisfactory for this purpose.
7 Versiloc 201 and 204 with accelerator, available from Lord Corp., IndustrialAdhesive Div., 2000 W. Grandview Blvd., P.O. Box 10038, Erie, PA 16514, havebeen found satisfactory for this purpose.
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NOTE 2—Guides D 2651 and D 3933 are typical of well-proven meth-ods for improving adhesive bond strengths to metal surfaces.
6.5 Prepare the adhesive in accordance with the adhesivemanufacturer’s recommendations. Apply the adhesive to thefixture or the surface to be tested, or both, using a methodrecommended by the adhesive manufacturer. Be certain toapply the adhesive across the entire surface. Position fixture onthe surface to be tested. Carefully remove the excess adhesivefrom around the fixture. (Warning—Movement, especiallytwisting, can cause tiny bubbles to coalesce into large holidaysthat constitute stress discontinuities during testing.)
NOTE 3—Adding about 1 percent of #5 glass beads to the adhesiveassists in even alignment of the test fixture to the surface.
6.6 Based on the adhesive manufacturer’s recommendationsand the anticipated environmental conditions, allow enoughtime for the adhesive to set up and reach the recommendedcure. During the adhesive set and early cure stage, a constantcontact pressure should be maintained on the fixture. Magneticor mechanical clamping systems work well, but systemsrelying on tack, such as masking tape, should be used with careto ensure that they do not relax with time and allow air tointrude between the fixture and the test area.
6.7 Scoring around the fixture violates the fundamentalin-situ test criterion that an unaltered coating be tested. Ifscoring around the test surface is employed, extreme care isrequired to prevent micro-cracking in the coating, since suchcracks may cause reduced adhesion values. Scored samplesconstitute a different test, and this procedure should be clearlyreported with the results.
NOTE 4—It is common to score around the test fixture when performingtests on cementitious substrates where the tensile strength of the substrateis significantly lower than either the pull-off or cohesive strength of thecoating system.
6.8 Note the approximate temperature and relative humidityduring the time of test.
7. Test Procedure
7.1 Test Methods:7.1.1 Test Method A — Fixed Alignment Adhesion Tester
Type I:7.1.1.1 Operate the instrument in accordance with Annex
A1.7.1.2 Test Method B — Fixed Alignment Adhesion Tester
Type II:7.1.2.1 Operate the instrument in accordance with Annex
A2.7.1.3 Test Method C — Self-Alignment Adhesion Tester Type
III :7.1.3.1 Operate the instrument in accordance with Annex
A3.7.1.4 Test Method D — Self-Alignment Adhesion Tester Type
IV:7.1.4.1 Operate the instrument in accordance with Annex
A4.7.1.5 Test Method E — Self-Alignment Adhesion Tester Type
V:7.1.5.1 Operate the instrument in accordance with Annex
A5.
7.2 Select an adhesion-tester with a detaching assemblyhaving a force calibration spanning the range of expectedvalues along with its compatible loading fixture. Mid-rangemeasurements are usually the best, but read the manufacturer’soperating instructions before proceeding.
7.3 If a bearing ring or comparable device (5.1.3) is to beused, place it concentrically around the loading fixture on thecoating surface. If shims are required when a bearing ring isemployed, place them between the tester base and bearing ringrather than on the coating surface.
7.4 Carefully connect the central grip of the detachingassembly to the loading fixture without bumping, bending, orotherwise prestressing the sample and connect the detachingassembly to its control mechanism, if necessary. For nonhori-zontal surfaces, support the detaching assembly so that itsweight does not contribute to the force exerted in the test.
7.5 Align the device according to the manufacturer’s in-structions and set the force indicator to zero.
NOTE 5—Proper alignment is critical, see Appendix X2. If alignment isrequired, use the procedure recommended by the manufacturer of theadhesion tester and report the procedure used.
7.6 Increase the load to the fixture in as smooth andcontinuous a manner as possible, at a rate of less than 1 MPa/s(150 psi/s) so that failure occurs or the maximum stress isreached in about 100 s or less (see Note 1).
7.7 Record the force attained at failure or the maximumforce applied.
7.8 If a plug of material is detached, label and store thefixture for qualification of the failed surface in accordance with8.3.
7.9 Report any departures from the procedure such aspossible misalignment, hesitations in the force application, etc.
8. Calculation and Interpretation of Results
8.1 If instructed by the manufacturer, use the instrumentcalibration factors to convert the indicated force for each testinto the actual force applied.
8.2 Either use the calibration chart supplied by the manu-facturer or compute the relative stress applied to each coatingsample as follows:
X 5 4F/pd 2 (1)
where:X = greatest mean pull-off stress applied during a pass/fail
test, or the pull-off strength achieved at failure. Bothhave units of MPa (psi).
F = actual force applied to the test surface as determinedin 8.1, and
d = equivalent diameter of the original surface areastressed having units of inches (or millimetres). Thisis usually equal to the diameter of the loading fixture.
8.3 For all tests to failure, estimate the percent of adhesiveand cohesive failures in accordance to their respective areasand location within the test system comprised of coating andadhesive layers. A convenient scheme that describes the totaltest system is outlined in 8.3.1 through 8.3.3. (See ISO 4624.)
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NOTE 6—A laboratory tensile testing machine is used in ISO 4624.
8.3.1 Describe the specimen as substrateA, upon whichsuccessive coating layersB, C, D, etc., have been applied,including the adhesive,Y, that secures the fixture,Z, to the topcoat.
8.3.2 Designate cohesive failures by the layers within whichthey occur asA, B, C, etc., and the percent of each.
8.3.3 Designate adhesive failures by the interfaces at whichthey occur asA/B, B/C, C/D, etc., and the percent of each.
8.4 A result that is very different from most of the resultsmay be caused by a mistake in recording or calculating. Ifeither of these is not the cause, then examine the experimentalcircumstances surrounding this run. If an irregular result can beattributed to an experimental cause, drop this result from theanalysis. However, do not discard a result unless there are validnonstatistical reasons for doing so or unless the result is astatistical outlier. Valid nonstatistical reasons for droppingresults include alignment of the apparatus that is not normal tothe surface, poor definition of the area stressed due to improperapplication of the adhesive, poorly defined glue lines andboundaries, holidays in the adhesive caused by voids orinclusions, improperly prepared surfaces, and sliding or twist-ing the fixture during the initial cure. Scratched or scoredsamples may contain stress concentrations leading to prema-ture fractures. Dixon’s test, as described in Practice D 3980,may be used to detect outliers.
8.5 Disregard any test where glue failure represents morethan 50 % of the area. If a pass/fail criterium is being used anda glue failure occurs at a pull-off strength greater than thecriterium, report the result as “pass with a pull-off strength>{value obtained}...”
8.6 Further information relative to the interpretation of thetest results is given in Appendix X2.
9. Report
9.1 Report the following information:9.1.1 Brief description of the general nature of the test, such
as, field or laboratory testing, generic type of coating, etc.9.1.2 Temperature and relative humidity and any other
pertinent environmental conditions during the test period.9.1.3 Description of the apparatus used, including: appara-
tus manufacturer and model number, loading fixture type anddimensions, and bearing ring type and dimensions.
9.1.4 Description of the test system, if possible, by theindexing scheme outlined in 8.3 including: product identity andgeneric type for each coat and any other information supplied,the substrate identity (thickness, type, orientation, etc.), and theadhesive used.
9.1.5 Test results.9.1.5.1 Date, test location, testing agent.9.1.5.2 For pass/fail tests, stress applied along with the
result, for example, pass or fail and note the plane of anyfailure (see 8.3 and ANSI N512).
9.1.5.3 For tests to failure, report all values computed in 8.2along with the nature and location of the failures as specified in8.3, or, if only the average strength is required, report theaverage strength along with the statistics.
9.1.5.4 If corrections of the results have been made, or ifcertain values have been omitted such as the lowest or highestvalues or others, reasons for the adjustments and criteria used.
9.1.5.5 For any test where scoring was employed, indicate itby placing a footnote superscript beside each data pointaffected and a footnote to that effect at the bottom of each pageon which such data appears. Note any other deviations from theprocedure.
10. Precision and Bias8
10.1 Precision—In an interlaboratory study of Test MethodsA-D, operators made measurements, generally in triplicate butin a few cases in duplicate, on coated panels covering amoderate range at the intermediate adhesion level using fourdifferent types of instruments (see Annex A1-Annex A5 andAppendix X1). The number of participating laboratories variedwith each instrument and in the case of one instrument with thematerial. Only two laboratories had access to Type I instru-ments but two operators in each made the triplicate tests.During the statistical analysis of the results three individualresults and one set of triplicates obtained with Type IIinstruments were rejected as outliers; one single test with TypeIII instruments and three single results with Type I instrumentswere rejected. The pooled intra- and inter-laboratory coeffi-cients of variation were found to be those shown in Table 1.
Based on these coefficients the following criteria should beused for judging, at the 95 % confidence level, the acceptabilityof results:
10.1.1 Replicate Repeatability—Triplicate results obtainedby the same operator using instruments from the same categoryshould be considered suspect if they differ in percent relativeby more than the values given in Table 1.
NOTE 7—Difference in percent relative to two results,x1 andx2, is theabsolute value of
~x1 2 x 2!
~x1 1 x2!/23 100. (2)
8 Supporting data are available from ASTM International Headquarters. RequestRR: D01-1094.
TABLE 1 Precision of Adhesion Pull-Off Measurements
InstrumentCoefficient ofVariation, v, %
Degrees ofFreedom
MaximumAcceptable
Difference, %
Intralaboratory Instrument:Type IV 8.5 48 29.0Type I JType II 12.2 129 41.0Type III
Total 177Interlaboratory Instrument:
Type IV 8.7 20 25.5Type I JType II 20.6 58 58.7Type III
Total 78
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10.1.2 Reproducibility—Two results, each the mean of trip-licates, obtained by operators in different laboratories usinginstruments of the same category should be considered suspectif they differ in percent relative by more than the values givenin Table 1.
10.2 Bias—This test method has no bias statement sincethere is no acceptable reference material suitable for determin-ing the bias of this test method.
11. Keywords
11.1 adhesion; coatings; field; paint; portable; pull-offstrength; tensile test
ANNEXES
(Mandatory Information)
A1. FIXED-ALIGNMENT ADHESION TESTER, TYPE I
A1.1 Apparatus:
A1.1.1 A fixed-alignment portable tester as shown in Fig.A1.19
NOTE A1.1—Precision data for Type I instruments described in Table 1were obtained using the devices illustrated in Fig. A1.1.
A1.1.2 The tester is comprised of detachable aluminumloading fixtures, 50 mm (1.97 in.) in diameter, screws withspherical heads that are screwed into the center of a fixture, asocket in the testing assembly that holds the head of the screw,pressure gage, dynamometer, wheel and crank.
A1.1.3 The testers are available in four models, with maxi-mum tensile forces of 5, 15, 25, and 50 kN (1125, 3375, 5625,and 11 250 lb ) respectively. For a fixture having a 50 mm (1.97in.) diameter, a 5 kNdevice corresponds to a range of 2.5 MPa(0 to 360 psi).
A1.2 Procedure:
A1.2.1 Follow the general procedures described in Sections6 and 7. Procedures specific to this instrument are described inthis section.
A1.2.2 Set the pointer on the zero mark by first pressing thepush-button located on the left of the indicator. While holdingthe push-button, turn the little knob located on the upper part ofthe indicator to set the pointer at zero. Set the zero after testingby pressing the push-button.
A1.2.3 After fixing a loading fixture to a substrate, insert ascrew with a spherical head into the center of the fixture.Position the testing equipment on the metal disc. Then bymeans of the notched wheel, fix the head of the spherical screwinto the socket at the base of the equipment. For the firstmechanical approach, stop screwing down the wheel when thepointer on the indicator shifts from the ZERO mark. Tests aredone by turning the crank. After each test, turn the crank in theopposite direction until it stops.
9 The Dyna Z5 tester is available from PROCEQ SA, Riesbachstrasse 57,CH-8034, Zurich, Switzerland.
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A2. FIXED-ALIGNMENT ADHESION TESTER TYPE II
A2.1 Apparatus:
A2.1.1 This is a fixed-alignment portable tester, as shown inFig. A2.1.10
NOTE A2.1—Precision data for Table 1 were obtained using the devicesillustrated in Fig. A2.1.
A2.1.2 The tester is comprised of detachable aluminumloading fixtures having a flat conic base that is 20 mm (0.8 in.)in diameter on one end for securing to the coating, and acircular T-bolt head on the other end, a central grip forengaging the loading fixture that is forced away from a tripodbase by the interaction of a handwheel (or nut), and a coaxialbolt connected through a series of belleville washers, or springsin later models, that acts as both a torsion relief and a springthat displaces a dragging indicator with respect to a scale.
10 The Elcometer, Model 106, adhesion tester is available from ElcometerInstruments, Ltd., Edge Lane, Droylston, Manchester M35 6UB, United Kingdom,England.
(a)
(b)
FIG. A1.1 Photograph (a) and sketch (b) of Type I instruments
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A2.1.3 The force is indicated by measuring the maximumspring displacement when loaded. Care should be taken to seethat substrate bending does not influence its final position orthe actual force delivered by the spring arrangement.
A2.1.4 The devices are available in four ranges: From 3.5,7.0, 14, and 28 MPa (0 to 500, 0 to 1000, 0 to 2000, and 0 to4000 psi).
A2.2 Procedure:
A2.2.1 Center the bearing ring on the coating surfaceconcentric with the loading fixture. Turn the hand wheel or nutof the tester counter-clockwise, lowering the grip so that it slipsunder the head of the loading fixture.
A2.2.2 Align or shim the three instrument swivel pads of thetripod base so that the instrument will pull perpendicularly tothe surface at the bearing ring. The annular ring can be used onflexible substrates.
A2.2.3 Take up the slack between the various members andslide the dragging (force) indicator located on the tester to zero.
A2.2.4 Firmly hold the instrument with one hand. Do notallow the base to move or slide during the test. With the otherhand, turn the handwheel clockwise using as smooth andconstant motion as possible. Do not jerk or exceed a stress rateof 150 psi/s (1 MPa/s) that is attained by allowing in excess of7 s/7 MPa (7 s/1000 psi), stress. If the 14 or 28 MPa (2000 or4000 psi ) models are used, the handwheel is replaced with anut requiring a wrench for tightening. The wrench must be usedin a plane parallel to the substrate so that the loading fixturewill not be removed by a shearing force or misalignment, thusnegating the results. The maximum stress must be reachedwithin about 100 s.
A2.2.5 The pulling force applied to the loading fixture isincreased to a maximum or until the system fails at its weakestlocus. Upon failure, the scale will rise slightly, while thedragging indicator retains the apparent load. The apparatusscale indicates an approximate stress directly in pounds persquare inch, but may be compared to a calibration curve.
A2.2.6 Record the highest value attained by reading alongthe bottom of the dragging indicator.
(a)
(b)
FIG. A2.1 Photograph (a) and schematic (b) of Type II, FixedAlignment Pull-Off Tester
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A3. SELF-ALIGNING ADHESION TESTER TYPE III
A3.1 Apparatus:
A3.1.1 This is a self-aligning tester, as shown in Fig. A3.1.11
NOTE A3.1—Precision data for Type II instruments shown in Table 1were obtained using the devices described in Fig. A3.1.
A3.1.2 Load is applied through the center of the dolly by ahydraulic piston and pin. The diameter of the piston bore issized so that the area of the bore is equal to the net area of thedolly. Therefore, the pressure reacted by the dolly is the sameas the pressure in the bore and is transmitted directly to apressure gage.
A3.1.3 The apparatus is comprised of: a dolly, 19 mm (0.75in.) outside diameter, 3 mm (0.125 in.) inside diameter,hydraulic piston and pin by which load is applied to the dolly,hose, pressure gage, threaded plunger and handle.
A3.1.4 The force is indicated by the maximum hydraulicpressure as displayed on the gage, since the effective areas ofthe piston bore and the dolly are the same.
A3.1.5 The testers are available in three standard workingranges: 0 to 10 MPa (0 to 1500 psi), 0 to 15 MPa (0 to 2250psi), 0 to 20 MPa (0 to 3000 psi). Special dollies shaped to testtubular sections are available.
A3.2 Procedure:
A3.2.1 Follow the general procedures described in Sections6 and 7. Procedures specific to this instrument are described inthis section.
A3.2.2 Insert a decreased TFE-fluorocarbon plug into thedolly until the tip protrudes from the surface of the dolly. Whenapplying adhesive to the dolly, avoid getting adhesive on theplug. Remove plug after holding the dolly in place for 10 s.
A3.2.3 Ensure that the black needle of the tester is readingzero. Connect a test dolly to the head and increase the pressureby turning the handle clockwise until the pin protrudes fromthe dolly. Decrease pressure to zero and remove the test dolly.
A3.2.4 Connect the head to the dolly to be tested, by pullingback the snap-on ring, pushing the head and releasing thesnap-on ring. Ensure the tester is held normal to the surface tobe tested and that the hose is straight.
A3.2.5 Increase the pressure slowly by turning the handleclockwise until either the maximum stress or failure is reached.
11 The Hate Mark VII adhesion tester is available from Hydraulic Adhesion TestEquipment, Ltd., 629 Inlet Rd., North Palm Beach, FL 33408.
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(a)
(b)
FIG. A3.1 Photograph (a) and schematic (b) of Type III, Self-Alignment Tester
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A4. SELF-ALIGNMENT ADHESION TESTER TYPE IV
A4.1 Apparatus:
A4.1.1 This is a self-aligning tester, which may have aself-contained pressure source and has a measuring system thatcontrols a choice of different load range detaching assemblies.It is shown in Fig. A4.1.12
NOTE A4.1—Precision data for Type IV instruments shown in Table 1were obtained using the devices illustrated in Fig. A4.1.
A4.1.2 The apparatus is comprised of: (1) a loading fixturehaving a flat cylindrical base that is 12.5 mm (0.5 in.) indiameter on one end for attachment to the test coating and acut-off ring used with the fixture to reproducibly define the areaof adhesive. The other end of the fixture has 3/8-16 UNCthreads; (2) a central threaded grip for engaging the loadingfixture through the center of the detaching assembly that isforced away by the interaction of a self-aligning seal; and (3)a pressurized gas that enters the detaching assembly through aflexible hose connected to a pressurization rate controller anda pressure gage (or electronic sensor).
A4.1.3 The force is indicated by the maximum gas pressuretimes the active area of the detaching assembly and can bedirectly calibrated.
A4.1.4 The detaching assemblies are available in six stan-dard ranges in multiples of two from 3.5 MPa (0 to 500 psi) to70 MPa (10 000 psi). Special ranges are available.
A4.1.5 Three models of control modules that control allranges of detaching assemblies are available.
A4.2 Procedure:
A4.2.1 Follow the general procedures described in Sections6 and 7. Procedures specific to Type IV testers are described inthe following section.
A4.2.2 Position the annular detaching assembly over thefixture attached to the coating to be tested, and loosely engagethe fixture via the central threaded grip. Leave at least 1.6-mm(1.16-in.) clearance between the detaching assembly and thebottom of the threaded grip so that the seal can protrudeenough to align itself when pressurized.
A4.2.3 Make the appropriate pneumatic connections andopen the rate valve 1/4 turn.
A4.2.4 Zero the pressure measuring system.
A4.2.5 Press the run button to control the gas flow to thedetaching assembly and make final adjustment of rate valve sothat rate of stress does not exceed 1 MPa/s (150 psi/s) yetreaches its maximum within 100 s.
A4.2.6 Record both the maximum pressure attained and thespecific detaching assembly. Conversion to coating stress for1⁄2-in. (12-mm) stud is found in a table supplied for eachdetaching assembly.
A5. SELF-ALIGNING ADHESION TESTER TYPE V
A5.1 Apparatus:
A5.1.1 This is a self-aligning tester, as shown in Fig. A5.113.
A5.1.2 Self-aligning spherical dolly head. Load evenlydistributes pulling force over the surface being tested, ensuringa perpendicular, balanced pull-off. The diameter of the standarddolly 20 mm (0.78 in.) is equal to the area of the position borein the actuator. Therefore, the pressure reacted by the dolly is
12 The PATTI self-alignment adhesion tester is available from SEMicro Corp.,15817 Crabbs Branch Way, Rockville, MD 20855.
13 The PosiTest Pull-Off Tester is available from DeFelsko Corporation, 802Proctor Avenue, Ogdensburg, NY 13669 USA.
(a)
FIG. A4.1 Photograph (a) and schematic of piston (b) of Type IVSelf-Alignment Adhesion Tester
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the same as the pressure in the actuator and is transmitteddirectly to the pressure gauge. Conversion charts and calcula-tions are provided for the 50 mm (1.97 in.) dollies and commoncustom sizes 10 and 14 mm (0.39 in. and 0.55 in. respectively).
A5.1.3 The apparatus is comprised of: a dolly, 20 to 50 mm(0.78 in. and 1.97 in. respectively) diameter, hydraulic actuatorby which the load is applied to the dolly, pressure gauge, andhydraulic pump.
A5.1.4 The drag pointer on the pressure gauge indicates themaximum force.
A5.1.5 The testers are available in two standard ranges 0 to7 MPa (0 to 1000 psi) with 20 mm (0.78 in.) dollies andaccessories for finishes on plastics, metals, and wood: 0 to 21MPa (0 to 3 100 psi) with 20 or 50 mm, or both, (0.78 in. or1.97 in., or both) dollies and accessories for coatings on metalsor concrete, or both. Special dollies, typically 10 mm (0.39 in.)and 14 mm (0.55 in.), are available for use on curved surfacesand when higher pull-off pressures are required.
A5.2 Procedure:
(a)
(b)
FIG. A5.1 Drawing (a) and schematic (b) of Type V, Self-Aligning Tester
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A5.2.1 Follow the general procedures described in Sections6 and 7. Procedures specific to Type V Testers are described inthis section.
A5.2.2 Ensure the pressure relief valve on the pump iscompletely open. Turn the “drag” indicator on the pressuregauge to zero. Push the actuator handle completely down intothe actuator assembly.
A5.2.3 Place the actuator assembly over the dolly head andattach the quick coupling to the dolly. Close the pressure reliefvalve on the pump.
A5.2.4 Ensure the pump is on a well-supported horizontalsurface. If it is necessary to place the pump on a vertical
surface, position the unit so the pump hose outlet is in the downposition to prevent air from being pumped into the actuator.Begin pumping the pump handle until the indicator on thepressure gauge starts to move. Continue pumping at a uniformrate of no more than 1 MPa/s (150 psi/s) until the actuator pullsthe dolly from the coating.
A5.2.5 Immediately following the pull, open the pressurerelief valve on the pump to release the pressure. The “drag”indicator on the pressure gauge will maintain the maximumpressure reading. Record the pull off pressure and mark thedolly for future qualitative analysis.
APPENDIXES
(Nonmandatory Information)
X1. INTERLABORATORY PULL-OFF DATA
X1.1 Table X1.1 is a summary of the interlaboratoryround-robin data. It is included in this appendix to illustrate thedependence of a pull-off result upon the type of testing device.
X2. STRESS CALCULATION
X2.1 The stress computed in 8.2 is equal to the uniformpull-off strength of the analogous rigid coating system if theapplied force is distributed uniformly over the critical locus atthe instant of failure. For any given continuous stress distribu-tion where the peak-to-mean stress ratio is known, the uniformpull-off strength may be approximated as:
U 5 XRo (X2.1)
where:U = uniform pull-off strength, representing the greatest
force that could be applied to the given surface area,psi (MPa),
X = measured in-situ pull-off strength calculated in 8.2,psi (MPa) and
Ro = peak-to-mean stress ratio for an aligned system.It is important to note that a difference between these pull-off
strengths does not necessarily constitute an error; rather thein-situ measurement simply reflects the actual character of theapplied coating system with respect to the analogous ideal rigidsystem.
X2.2 An error is introduced if the alignment of theapparatus is not normal to the surface. An approximatecorrection by the peak-to-mean stress ratio is:
R5 Ro ~1 1 0.14az/d!, (X2.2)
where:z = distance from the surface to the first gimbal or the
point at which the force and counter force are gener-ated by the action of the driving mechanism, in. (mm),
d = diameter of the loading fixture, in. (mm),a = angle of misalignment, degrees (less than 5), andR = maximum peak-to-mean stress ratio for the misaligned
rigid system.
TABLE X1.1 Summary of Round-robin Data
Instrument Type I Type II Type III Type IV
Paint Sample Mean of Three Results, psi (outliers discarded)
A 201 586 1185 1160B 185 674 1157 1099C 190 827 1245 1333D 297 888 1686 1678
Range of Mean Results, psi112 302 529 579
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ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.
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7-7
SSPC-PA 1April 1, 2000
Editorial Revisions November 1, 2004
SSPC: The Society for Protective Coatings
PAINT APPLICATION SPECIFICATION NO. 1Shop, Field, and Maintenance Painting of Steel
1. Scope
1.1 This specification covers procedures for the painting of steel surfaces. The scope of this specification is rather broad, covering both specific as well as general requirements for the application of paint. This specification does not provide detailed descriptions of surface preparation, pretreatments, or selection of primers and finish coats. This specification does provide detailed coverage of the procedures and methods for application after the selection of the coating materials has been made.
2. Description
2.1 This specification for shop, field, and maintenance painting is intended to be used for steel which, because of its exposure condition, will be subjected to corrosive attack, either from the weather or from the service environment, and where a high quality of cleaning and painting is essential. It is not contemplated that the requirements of this specification are necessary for the cleaning and painting of steel which will not be subjected to corrosive attack. The following is a summary of the major sections of this specification.
1. Scope 2. Description 3. Reference Standards 4. Definitions 5. Pre-Application Procedures 5.1 Materials Handling and Use 5.2 Surface Preparation 5.3 Pretreatments 5.4 Coating Materials Preparation6. Factors Affecting the Application of Coatings 6.1 Temperature 6.2 Moisture 6.3 Humidity 6.4 Cover 6.5 Defects 6.6 Striping 6.7 Continuity 6.8 Thickness 6.9 Recoating 6.10 Tinting 6.11 Intercoat Adhesion 6.12 Contact Surfaces 6.13 Induction Time and Pot Life7. Application Methods 7.1 General 7.2 Brush Application 7.3 Roller Application
7.4 Spray Application (General) 7.5 Air Atomizing Spray Application 7.6 Airless Spray Application 7.7 Air-Assisted Airless Application 7.8 Hot Air Spray Application 7.9 Hot Airless Spray Application 7.10 Plural Component Spray Application 7.11 High Volume Low-Pressure Spray8. Shop Coating 8.1 Applicability 8.2 Number of Coats and Type of Coating 8.3 Damage to Shop Coating 8.4 Contact Surfaces 8.5 Requirements for Welding 8.6 Rust Preventive Compounds 8.7 Erection Marks9. Field Coating 9.1 Applicability 9.2 Surface Preparation 9.3 Touch-up of Shop Coated Surfaces 9.4 Field Coating Procedures10. Repair of Damaged Intact Coatings 10.1 Applicability 10.2 Surface Preparation for Recoating 10.3 Incompatibility 10.4 Work to be Performed11. Application Procedures for Generic Groups of Coatings 11.1 General 11.2 Drying Oil Curing Coatings 11.3 Vinyls and Chlorinated Rubber Coatings 11.4 Bituminous Coatings 11.5 Epoxy and Coal Tar Epoxy Coatings 11.6 Zinc-Rich Coatings 11.7 Urethane Coatings 11.8 Waterborne Thermoplastic Coatings12. Curing and Handling of Coatings 12.1 Drying of Coatings 12.2 Handling of Coated Steel13. Inspection 14. Safety and Environmental Concerns 15. Disclaimer 16. Notes Appendix A - Additional Reference Materials
3. Referenced Standards
3.1 The latest issue, revision, or amendment of the refer-enced standards in effect on the date of invitation to bid shall govern unless otherwise specified.
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3.2 If there is a conflict between the requirements of any of the cited reference standards and this specification, the requirements of this specification shall prevail.
3.3 SSPC: THE SOCIETY FOR PROTECTIVE COAT-INGS STANDARDS:
PA 2 Measurement of Dry Coating Thick-ness With Magnetic Gages
PA Guide 3 A Guide to Safety in Paint Applica-tion
SP 1 Solvent Cleaning (not referenced in body of spec)
3.4 AMERICAN SOCIETY FOR TESTING AND MATE-RIALS (ASTM) STANDARDS:
D 16 Standard Terminology for Paint, Related Coatings, Materials, and Applications
D 4285 Method for Indicating Oil or Water in Com-pressed Air
3.7 NACE INTERNATIONAL STANDARD:* RP0178 Fabrication Details, Surface
Finishing Re-quirements, and Proper Design Considerations for Tanks and Vessels to be Lined for Immersion Service
4. Definitions
4.1 SHOP, FIELD AND MAINTENANCE COATING: The application of coatings to steel surfaces whether in the shop or in the field.
4.2 PAINT: In the general sense, paint includes primers, enamels, varnishes, emulsions, catalyzed coatings, bituminous coatings, and other organic coatings. Inorganic coatings which are also applied as liquid films are included in this definition. This definition is compatible with most commonly used industry glossaries.
4.3 SHOP COATING: The surface preparation and coat-ing of steel surfaces inside a shop or plant before shipment to the site of erection.
4.4 FIELD COATING: The on-site coating of new or previ-ously coated steel structures before or after erection.
4.5 MAINTENANCE COATING: The coating of steel structures in service that have been previously coated and require touch-up or recoating.
4.6 MANUFACTURERʼS INSTRUCTIONS AND REC-OMMENDATIONS: These (or similar terms) are used to refer to an equipment supplierʼs or coating manufacturerʼs latest published or written instructions and recommendations. Verbal recommendations or instructions from an equipment or coating manufacturer are not acceptable unless backed up in writing by the manufacturerʼs technical staff.
5. Pre-Application Procedures
See Section 11 for procedures unique to specific generic coatings.
5.1 MATERIALS HANDLING AND USE
5.1.1 All coating shall be delivered to the shop or jobsite in original, unopened containers with labels intact. Minor dam-age to containers is acceptable provided the container has not been punctured or the lid seal broken.
5.1.2 Each container of coating shall be clearly marked or labelled to show coating identification, date of manufacture, batch number, and other information as needed to meet regula-tory requirements. Each type of coating shall be accompanied by the manufacturerʼs Material Safety Data Sheet (MSDS) and product data sheet containing information such as basic chemical composition, weather conditions acceptable for ap-plication, and proper storing and mixing.
5.1.3 All containers of coating shall remain unopened until required for use. No more containers of coating shall be opened than will be applied that day. The label information shall be legible and shall be checked at the time of use.
5.1.4 Coating which has livered, gelled, or otherwise dete-riorated during storage shall not be used; however, thixotropic materials which can be stirred to attain normal consistency may be used.
5.1.5 The oldest coating of each kind that is in acceptable condition shall be used first. In every case, coating is to be used before its shelf life has expired. Before using a coating which has exceeded its shelf life, the manufacturer shall verify its quality and then certify its use for a given period of time.
5.1.6 Coatings shall be stored in original unopened containers in weathertight spaces where the temperature is maintained between 40 °F and 100 °F (4 °C and 38 °C) unless otherwise recommended in writing by the manufacturer. The coating temperature shall be brought to the manufacturerʼs written recommended application temperature before use. (See Note 16.1 for more information on coating storage.)
5.2 SURFACE PREPARATION
5.2.1 The surface shall be cleaned as specified in the procurement documents. In no event shall the surface prepara-tion be less than the paint manufacturerʼs recommendations for the intended service environment.
5.2.2 The surface to be coated shall have the specified surface preparation at the time of application of the coating. If the surface is degraded or contaminated subsequent to
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surface preparation and prior to coating, the surface shall be restored to the specified condition before coating application (see Note 16.2).
5.2.3 In order to control the degradation or contamination of cleaned surfaces, the pretreatments, or, in the absence of a pretreatment, the prime coat shall be applied as soon as possible after the surface has been cleaned and before degradation or contamination has occurred. Succeeding coats shall be applied before contamination of any existing coating occurs.
5.2.4 Previously applied coating shall be roughened prior to coating whenever necessary for the development of proper intercoat adhesion (see Section 6.11).
5.2.5 Cleaning and coating shall be scheduled to minimize the amount of dust and other contaminants that may fall on newly applied wet coating films. Surfaces not intended to be coated shall be suitably protected from the effects of cleaning and coating operations.
5.3 PRETREATMENTS
5.3.1 When specified, the surface shall be pretreated prior to application of the prime coat of coating
.5.3.2. The provisions of Sections 5.1 and 5.2 shall also
apply to pretreated surfaces and the materials used for this purpose.
5.3.3 When chemical pretreatments are used, sufficient time shall elapse between pretreatment and application of the prime coat to permit any chemical action to be completed and the surface to dry. Two-component pretreatments shall be ap-plied within the specified interval after mixing. When proprietary pretreatments are used, the instructions of the manufacturer shall be followed.
5.3.4 Inhibitive water washes used to prevent rusting of cleaned surfaces prior to coating shall not be considered pre-treatments. These may be used only if they do not adversely affect the long term performance of the coating and are specifi-cally authorized. Test patches may be used to check adhesion of the coating prior to coating the entire surface.
5.4 COATING MATERIALS PREPARATION
5.4.1 Single component coatings shall be thoroughly mixed to obtain a uniform composition. For multiple component coatings, each component shall be thoroughly mixed before combining and further mixing. In all cases, the manufacturerʼs written instructions for mixing shall be followed, and the products shall be checked for complete uniformity.
5.4.2 The following are acceptable methods for mixing most coatings:
5.4.2.1 Manual (Hand) Mixing: Most of the vehicle shall be poured off into a clean container. The pigment in the coating shall be lifted from the bottom of the container with a broad, flat paddle, lumps shall be broken up, and the pigment thoroughly mixed with the remaining vehicle. The poured off vehicle shall be returned to the coating with simultaneous stirring, or boxed until the composition is uniform. “Boxing” is the process of mixing coating by pouring from one container to another. The maximum container size for “boxing” shall be five gallons.
5.4.2.2 Power Mixing: This will usually give better mixing in a much shorter time than mixing by hand.
5.4.3 All pigmented coating shall be strained after mixing except where application equipment is provided with strainers. Strainers shall be of a size to remove only skins and undesir-able matter but not to remove the pigment.
5.4.4 Where a skin has formed in the container, the skin shall be cut loose from the sides of the container, removed and discarded. If the volume of such skins is visually estimated to be more than 2% of the remaining coating, the coating shall not be used.
5.4.5 Mixing of solvent-containing coatings in open containers shall be done in a well ventilated area away from sparks or flames.
5.4.6 Coating shall not be mixed or kept in suspension by means of an air stream bubbling under the coating surface.
5.4.7 Dry pigments which are separately packaged shall be mixed into coatings in such a manner that they are uniformly blended and all particles of the dry powder are wetted by the vehicle.
5.4.8 Pastes shall be made into coatings in such a manner that the paste shall be uniformly blended and all lumps and particles broken up to form a homogenous coating.
5.4.9 Coating which does not have a limited pot life or does not deteriorate on standing may be mixed at any time before using, but if settling or phase separation has occurred it must be remixed immediately before using.
5.4.10 Coating shall not remain in spray pots, paintersʼ buckets, etc., overnight, but shall be stored in a covered con-tainer and remixed before use.
5.4.11 Catalysts, curing agents, or hardeners which are separately packaged shall be added to the base coating only after the latter has been thoroughly mixed. The proper volume of the catalyst shall then be slowly poured into the required volume of base with constant agitation. Mixing of complete kits is preferred to avoid mixing incorrect ratios of
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components. Do not pour off the liquid which has separated from the pigment and then add the catalyst to the settled pig-ment to aid mixing. The mixture shall be used within the pot life specified by the manufacturer. For example, more than 20 minutes and less than eight hours after mixing are the pot life limits for some chemically cured coatings (see Section 6.13). Therefore only enough coating should be catalyzed for prompt use. Most mixed, catalyzed coatings cannot be stored, and unused portions of these shall be placed in proper storage containers for later appropriate disposal. When specified, special continuous mixing equipment shall be used according to the manufacturerʼs directions.
5.4.12 Thinning of the coating shall be done only when necessary for proper application and when it will not result in violation of air pollution control regulations. Coatings to be ap-plied by brush will usually require no thinning. Coatings to be sprayed, if not specifically formulated for spraying, may require thinning when proper adjustment of the spray equipment and air pressure does not result in satisfactory coating application. In no case shall more thinner be added than that recommended by the manufacturerʼs written instructions.
5.4.13 The type of thinner shall comply with the manu-facturerʼs instructions.
5.4.14 When the use of thinner is permissible, thinner shall be added slowly to coating during the mixing process. All thinning shall be done under supervision of a knowledge-able person acquainted with the correct amount and type of thinner to be added to the coating and familiar with pertinent regulations relating to solvent emissions. Thinner should be at the same temperature as the coating material. At very low temperatures, thinners can shock sensitive coating materials, resulting in gelling.
6. Factors Affecting Application of Coatings
See Section 11 for factors unique to specific generic coatings.
6.1 TEMPERATURE: The application of a coating system shall occur only when the air and substrate temperature is within the range indicated by the manufacturerʼs written instructions for both application and curing and can be expected to remain in that range. Special coating materials are available that would allow for application below 60°F with or without further adjustment. (See Note 16.3.)
6.2 MOISTURE: Coating shall not be applied in rain, wind, snow, fog, or mist, or when the steel surface temperature is less than 5 °F (3 °C) above the dew point. Coating shall not be applied to wet or damp surfaces unless the coating is formulated and certified by the manufacturer for this type of application. Coating shall not be applied on frosted or ice-coated surfaces (see Note 16.4).
6.3 HUMIDITY: Because curing of coatings may be adversely affected by humidities that are too low or too high, no coating shall be applied unless the manufacturerʼs written requirements for humidity are met.
6.3.1 Some coatings (e.g., some inorganic zinc and poly-urethane coatings) cure by chemically reacting with water, and so require a minimum humidity for complete curing.
6.3.2 High humidities may cause moisture to condense on or react with uncured coating films to cause blushing or other adverse effects.
6.4 COVER: When coating must be applied in damp or cold weather, the steel must be coated when the surrounding air and the steel are heated to a satisfactory temperature. In all such cases, the temperature and moisture conditions of Sections 6.1 and 6.2 must be met. Where cover is required to achieve these conditions, the steel shall remain under cover or be protected until dry or weather conditions permit its ex-posure.
6.5 DEFECTS: Defects in films that are not permitted by the contract specification shall be corrected in a manner satisfactory to the owner.
6.6 STRIPING: If stripe coating is specified in the procure-ment documents, all corners, crevices, rivets, bolts, welds, and sharp edges shall be stripe coated with the priming coating before the steel receives its first full prime coat of coating. Such striping shall extend a minimum of one inch (2 cm) from the edge. The stripe coat shall set to touch before the full prime coat is applied. However, the stripe coat shall not be permitted to dry for a period long enough to allow rusting of the unprimed steel. Alternatively, the stripe coat may be applied after a complete prime coat.
Stripe coating of edges, corners, rivets, welds, etc., is advantageous in preventing breakdown of coating on such edges in very corrosive surroundings. Striping is an expensive operation and may only be justified when it is believed the cost will be compensated for by extra life. To prevent removal of the stripe coat of coating by later application of the prime coat, the striped coating should be allowed to at least set to touch before application of the full prime coat; a longer drying period is advantageous, however. Where it is felt that a long drying period of stripe is necessary, but the precoated steel will deteriorate in the interval, the full prime coat of coating may be applied, allowed to dry, and the stripe coating then applied. Tinting of the striping coating is advisable to promote contrast (see Section 6.10). Stripe coating is most effective on edges that are rounded by grinding.
6.7 CONTINUITY: To the maximum extent practical, each coat shall be applied as a visually continuous film of uniform thickness free of pores. All thin spots or areas missed in the application shall be recoated and permitted to dry before the next coat of coating is applied.
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6.8 THICKNESS: Unless otherwise specified in the pro-curement documents, all dry film thickness determinations shall be performed as specified in PA 2, Measurement of Dry Coating Thickness with Magnetic Gages. Coating thickness is usually specified (or implied) as a minimum. Greater thickness that does not detrimentally affect the appearance or service life of the coating is permitted unless otherwise specified.
6.8.1 If not otherwise specified, each prime coat shall be within a thickness range of 1.5 mils (38 micrometers) to 2.5 mils (64 micrometers) when dry. Each intermediate and finish coat shall be within a thickness range of 1.0 mils (25 micrometers) to 2.0 mils (51 micrometers). As indicated in Section 11, vinyls, lacquers, emulsions, high-build coatings, and bituminous coat-ings usually deviate from these thicknesses.
6.8.2 In the event the required minimum thickness is not achieved as specified, additional coats shall be applied in ac-cordance with the manufacturerʼs instructions until the required thickness is obtained. The inorganic zinc-rich coatings shall not be corrected in this manner unless the manufacturer's instructions specifically permit this practice.
6.9 RECOATING: Each coating layer shall be in a proper state of cure or dryness before the application of the succeeding coat so that it is not adversely affected by topcoating. Consult the coating manufacturer for the appropriate time interval before recoating.
6.10 TINTING: When successive coats of coating of the same color have been specified, alternate coats of coating shall be tinted, when practical, to produce enough contrast to indicate complete coverage of the surface. Tinting shall be performed in such a manner that it will not be necessary to tint the final coat. Field tinting shall be done only with coatings of the same type from the same manufacturer. When the coating is the color of the steel, the first coat to be applied shall be tinted. The tinting material shall be compatible with the coat-ing and not detrimental to its service life. It is suggested that the coating be tinted by the manufacturer and appropriately labeled. Single component coatings to be blended for tinting shall be thoroughly mixed separately before combining and further mixing. For multiple-components, it is necessary to blend similar components of the two different colors together before combining and mixing these blends.
6.11 INTERCOAT ADHESION: When applying multiple coats of two component thermosetting systems, topcoats shall be applied within the recoat window specified by the manufacturer of the undercoat in order to obtain good intercoat adhesion. If, for any reason, this time period is exceeded, the undercoat surface shall be specially treated as recommended by its manufacturer before topcoating. Such treatments include mild abrasion, solvent treatment, and use of a fog coat.
6.12 CONTACT SURFACES: Unless otherwise required by the contract specification, the following practice shall be followed regarding coating of contact surfaces.
6.12.1 Steel to be embedded, encased or completely enclosed in brick or masonry shall be given at least one coat of coating that is compatible with masonry materials.
6.12.2 The areas to be in contact with wood shall receive the full specified coating system before assembly.
6.12.3 Surfaces to be in contact only after field erection shall receive the full-specified coating system before assembly.
6.12.4 Steel surfaces not in direct bonded contact, but inaccessible after assembly, shall receive the full-specified coating system before assembly.
6.12.5 Contact surfaces of members to be joined by high strength bonds in a friction connection are a special case. Unless specifically authorized to the contrary, they shall be left uncoated and free of oil, grease, and coatings. However, faying surfaces of friction connection may be coated with ap-proved coatings which do not release the coefficient of friction between contact surfaces, in accordance with the American Institute of Steel Construction (AISC) and the Research Council on Structural Connections (RCSC).
6.13 INDUCTION TIME AND POT LIFE: The induction time (sometimes called “sweat-in time”) and pot life require-ments of the manufacturer shall be met.
7. Application Methods
See Section 11 for application methods unique to specific generic coatings.
7.1 GENERAL
7.1.1 The following methods of application are covered by this specification: brush, roller, air spray, airless spray, plu-ral component spray, hot spray, or any combination of these methods. Daubers or natural or synthetic wool mitts or other applicators may be used for places of difficult access when no other method is practical. Whichever application method is used, the dry film thickness of each coat shall meet the requirement of the specification or the manufacturerʼs recommendation, whichever has precedence, as agreed upon by owner and contractor. Also see Note 16.5.
7.1.2 The following methods of application are not covered by this specification: dipping, flow coating, electrostatic spray, and fluidized bed. If application by one of these methods is specified, it shall be done in accordance with the procurement
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documents or, if none are present, with the manufacturer's recommendations.
7.2 BRUSH APPLICATION: Brush application of coating shall be in accordance with the following:
7.2.1 Brushes shall be of a style and quality that will en-able proper application of coating. Round or oval brushes are generally considered most suitable for rivets, bolts, irregular surfaces, and rough or pitted steel. Wide, flat brushes are suitable for large flat areas, but they should not have a width over five inches.
7.2.2 The brushing shall be done so that a smooth coat as uniform in thickness as possible is obtained.
7.2.3 Coating shall be worked into all crevices and cor-ners.
7.2.4 All runs or sags shall be brushed out (see 7.3.4).
7.2.5 An attempt shall be made to minimize brush marks and other surface irregularities.
7.3 ROLLER APPLICATION: Roller application shall be in accordance with the following:
7.3.1 Rolling shall be done so that a smooth coat as uniform in thickness as possible is achieved.
7.3.2 Roller covers shall be selected which do not shed fibers into the paint. Their nap should be appropriate for the particular surface roughness.
7.3.3 Roller application may be used on flat or slightly curved surfaces and shall be in accordance with the recom-mendations of the coating manufacturer and roller manufacturer. Coating rollers shall be of a style and quality that will enable proper application of coating having the continuity and thick-ness required in Sections 6.7 and 6.8.
7.3.4 Roller application shall not be used on irregular surfaces such as rivets, bolts, crevices, welds, corners, or edges, unless otherwise specified. When permitted, however, the coating applied by roller on these irregular surfaces shall be subsequently brushed out to form a continuous and unbroken film (see Note 16.6).
7.4 SPRAY APPLICATION (GENERAL): All spray ap-plication of coating, whether air spray, airless spray, plural-component spray, hot air spray or hot airless spray, shall be in accordance with the following:
7.4.1 The equipment used shall be suitable for the intended purpose, shall be capable of properly atomizing the coating
to be applied, and shall be equipped with suitable pressure regulators and gages. The equipment shall be maintained in proper working condition. Spray equipment shall meet the material transfer requirements of the local air pollution or air quality management district.
7.4.2 Coating ingredients shall be kept uniformly mixed in the spray pots or containers during coating application either by continuous mechanical agitation or by intermittent agitation as frequently as necessary.
7.4.3 Spray equipment shall be kept sufficiently clean so that dirt, dried coating, and other foreign materials are not deposited in the coating film. Any solvents left in the equipment shall be completely removed before using.
7.4.4 Coating shall be applied in a uniform layer with overlapping at the edges of the spray pattern. During applica-tion, the gun shall be held perpendicular to the surface and at a distance which will ensure that a wet layer of coating is deposited on the surface. The trigger of the gun should be released at the end of each stroke.
7.4.5 All runs and sags shall be brushed out immediately, and if not, the coating shall be removed and the surface re-painted. The wet film may be removed or allowed to dry and removed by sanding after curing.
7.4.6 Cracks, crevices, blind areas of all rivets and bolts, and all other inaccessible areas shall be coated by brush or daubers.
7.4.7 Particular care shall be observed with respect to type of thinner, amount of thinner, coating temperature, and operating techniques in order to avoid deposition of coating which is too viscous, too dry, or too thin. It may be necessary to use an approved different coating material or other equip-ment to resolve these problems.
7.4.8 Coatings formulated for application to hot surfaces may not be suitable for application to surfaces below the designed temperature. Conversely, coatings formulated for application at ambient or low temperatures may not be suitable for application to hot surfaces. Thus, coatings shall not be ap-plied outside the manufacturerʼs recommended temperature range without the written approval of the manufacturer and the owner.
7.5 AIR ATOMIZING SPRAY APPLICATION: Com-pressed air atomizing spray application of coating shall be in accordance with all the provisions of Section 7.4 and in addition shall comply with the following:
7.5.1 The air caps, nozzles, and needles shall be those rec-ommended by the manufacturers of the material being sprayed and the manufacturers of the equipment being used.
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7.5.2 Traps or separators shall be provided to remove any oil or condensed water from the air. The traps or separators must be of adequate size and must be bled continuously or drained periodically during operations. The air from the spray gun impinging against a clean surface shall show no condensed water or oil. ASTM D 4285 provides a test procedure for indi-cating the presence of oil or water in compressed air.
7.5.3 The pressure on the material in the pot and of the air at the gun shall be adjusted for optimum spraying effectiveness. The pressure on the material in the pot shall be adjusted when necessary for changes in elevation of the gun with respect to the elevation of the pot. The atomizing air pressure at the gun shall be high enough to properly atomize the coating, but not so high as to cause excessive fogging of coating, excessive evaporation of solvent or loss by overspray.
7.6 AIRLESS SPRAY APPLICATION: Airless or high pressure spray application of coating shall be in accordance with all of the provisions of Section 7.4 and in addition shall comply with the following:
7.6.1 Fluid tips shall be of proper orifice size and fan angle, and the fluid control gun of proper construction, as recommended by the manufacturer of the material being sprayed and the manufacturer of the equipment being used. Fluid tips shall be of the safety type with shields to prevent accidental penetration of the skin by the high pressure stream of coating.
7.6.2 The air pressure to the coating pump shall be adjusted so that the coating pressure to the gun is proper for optimum spraying effectiveness. This pressure shall be sufficiently high to properly atomize the coating. Pressures considerably higher than those necessary to properly atomize the coating should not be used.
7.6.3 Spraying equipment shall be kept clean and shall utilize proper filters in the high pressure line so that dirt, dry coating, and other foreign materials are not deposited in the coating film. Any solvents left in the equipment shall be com-pletely removed before applying coating.
7.6.4 The trigger of the gun should be pulled fully open and held fully open during all spraying to ensure proper application of coating. During application, the gun shall be held perpendicular to the surface and at a distance which will ensure that a wet layer of coating is deposited on the surface. The trigger of the gun should be released at the end of each stroke.
7.6.5 Airless coating spray equipment shall always be provided with an electric ground wire in the high pressure line between the gun and the pumping equipment. Further, the pumping equipment shall be suitably grounded to avoid the build-up of any electrostatic charge on the gun. The
manufacturerʼs instructions are to be followed regarding the proper use of the equipment. PA 3 provides information on how to use airless spray equipment safely.
7.7 AIR ASSISTED AIRLESS SPRAY: Air-assisted air-less spray atomizes paint by a combination of hydraulic and air pressures. Air-assisted airless spray shall be performed in accordance with all provisions of Sections 7.3 and 7.4.
7.8 HOT AIR SPRAY APPLICATION: Hot air spray ap-plication shall be in accordance with the provisions of Sections 7.4 and 7.5.
7.9 HOT AIRLESS SPRAY APPLICATION: Hot airless spray application shall be in accordance with Sections 7.4 and 7.6.
7.10 PLURAL COMPONENT SPRAY APPLICATION: Plural component spray shall be in accordance with all the provisions of Section 7.4 and use either fixed or variable ratio systems depending upon the ratio of components.
Plural component spray is used primarily for thick-film applications of fast-setting coatings.
7.11 HIGH-VOLUME LOW-PRESSURE SPRAY: High-volume low-pressure spray shall be in accordance with all the provisions of Section 7.4.
High-volume low-pressure spray has a high transfer ef-ficiency and can be used where other equipment with lower transfer efficiency is not permitted, as well as under less restrictive conditions.
8. Shop Coating
8.1 APPLICABILITY: All provisions of this specification shall be applicable to shop coating except those under Sec-tions 9 and 10.
8.2 NUMBER OF COATS AND TYPE OF COATING: The number of coats, type of coating, and surfaces to be coated shall be specified in the procurement documents. If coating thickness is not specified, the guidance in Section 6.8.1 shall be followed. The coating application shall be scheduled to provide protection to the substrate at all construction stages (see Note 16.7).
8.3 DAMAGE TO SHOP COATING: Damage resulting from fabrication, handling and storage in the shop shall be re-paired before leaving the shop. If the shop coating is damaged in shipping, unloading or field handling or fabrication, it shall be repaired before the field coating operations are begun.
8.4 CONTACT SURFACES: Contact surfaces shall be coated or left uncoated as specified in the procurement documents. When coated, the specification may require that
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at least the first coat shall be applied in the shop or the field, with subsequent coats being applied in the field while the surfaces are still accessible, unless otherwise specified (see Section 6.12).
8.5 REQUIREMENTS FOR WELDING:
8.5.1 If the coating specified is harmful to the welders (usually the case) or is detrimental to the welding operation or the finished welds, the steel shall not be coated within four inches (100 millimeters) of the areas to be welded, except when using inorganic zinc-rich primer, which may be applied to within one inch (25 millimeters) of the weld area.
8.5.2 Shop welds and areas within four inches of such welds shall be cleaned in the shop using surface preparation methods at least as effective as those specified for the struc-ture itself. All welds shall either be blast cleaned, thoroughly power tool cleaned, chemically scrubbed, or water scrubbed of all detrimental welding deposits.
8.6 RUST PREVENTIVE COMPOUNDS: Machine finished or similar surfaces that should not be coated, but do require protection, shall be protected as specified.
8.7 ERECTION MARKS: Erection and weight marks shall be placed on areas that have been previously shop primed unless otherwise specified. Compatible and non-bleeding markers or coating sticks shall be used
.9. Field Coating
9.1 APPLICABILITY: All provisions of this specification shall pertain to the field coating of steel structures except for inapplicable provisions of Sections 8 and 10.
9.2 SURFACE PREPARATION: Previously applied shop coatings must be dry or cured sufficiently for overcoating and be free of dirt, oil, chlorides, or other contaminants. The manufacturerʼs instructions shall be followed if special surface preparation procedures are required before application of the field coats. Damaged areas of shop applied coatings are to be touched-up in compliance with the requirements of Section 9.3. See SSPC-TU 4 for additional information on detection of soluble salts on steel surfaces.
9.3 TOUCH-UP OF SHOP COATED SURFACES: Steel that has been shop coated shall be touched up with the same coating as the shop coat unless otherwise specified. This touch-up shall include preparing, cleaning and coating of field connections, welds or rivets, and all damaged or defective coating and rusted areas as specified.
9.4 FIELD COATING PROCEDURES
9.4.1 Shop coated steel members shall preferably be field coated after erection of such members is completed. Steel members may be shop or field coated on the ground before erection, provided any damaged coating is touched-up with the same number of coats and kinds of coatings after erection. Whenever possible, the last full (finish) coat of coating shall be applied after erection of the structure and repair of damaged areas of existing coating.
9.4.2 The first field coat shall be applied to shop-coated steel in a timely manner, as required by the specification, to protect the steel from corrosion.
9.4.3 In the unlikely case that the types of field coatings are not specified, they shall be determined to be compatible with the shop coating and the service environment.
9.4.4 Contact surfaces shall be cleaned and coated as specified, unless otherwise stated in the procurement docu-ments (see Section 6.12).
9.4.5 When specified, surfaces (other than contact surfaces) of fabricated assemblies that are accessible before erection but which will not be accessible after erection shall receive the entire specified coating system before erection.
9.4.6 Coating shall be applied to all cracks and crevices as required by the specification.
9.4.7 The final coat of coating shall not be applied until all concrete work is finished. In addition to the cleaning specified in Section 5.2, all cement or concrete spatter and drippings shall be removed before any application of coating. If any coating is damaged, the damaged surface shall be cleaned and recoated before the final coat is applied.
9.4.8 Wet coating shall be protected against damage from dust or other detrimental foreign matter as much as is practical.
9.4.9 Steel stored pending erection shall be kept free from contact with the ground and so positioned as to minimize water-holding pockets, soiling, contamination, and deterioration of the coating film. Such steel shall be cleaned and recoated or touched-up with the specified coating whenever it becomes necessary to maintain the integrity of the film.
9.4.10 All field welds and all areas within four inches of welds shall be cleaned before painting, using surface prepa-ration methods at least as effective as those specified for the structure itself. All welds shall either be blast cleaned, thoroughly
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power tool cleaned, chemically scrubbed, or water scrubbed of all detrimental welding deposits.
10. Repair of Damaged Intact Coatings
10.1 APPLICABILITY: All provisions of this specification shall pertain to maintenance coating except the inapplicable portions of Sections 8 and 9.
10.2 SURFACE PREPARATION FOR RECOATING
10.2.1 Only loose, cracked, brittle, or non-adherent coating shall be removed in cleaning unless it is otherwise specified. Cleaning shall be performed two inches (50 micrometers) beyond the damaged areas in all directions or until tightly adhered coating is obtained. Where the remaining coating is thick, all exposed edges shall be feathered. Rust spots shall be thoroughly cleaned and the edges of all old coating shall be scraped back to sound material (see Note 16.9).
10.2.2 The contractor shall have the option to remove all coating from large areas containing smaller areas of coating which are required to be removed by the contract specification.
10.3 INCOMPATIBILITY: Only coatings compatible with the existing coatings and the service environment shall be used. All defects arising from unexpected incompatibility shall be corrected as specified.
10.4 WORK TO BE PERFORMED: The amount of clean-ing and coating should be described in the procurement docu-ments covering the work. It is important that the procurement documents cover precisely the work to be performed to avoid misunderstandings. In the absence of such specific provisions, the guidelines given in Note 16.9 may be used.
11. Application Procedures for Generic Groups of Coatings
11.1 GENERAL: The materials covered herein are to be applied as specified. In case of conflict with any other portion of this specification, these special provisions shall govern. Minimum and maximum dry film thicknesses are indicated, but thicker coatings should be applied when recommended by the manufacturerʼs instructions. Materials which are not specifically covered in this specification shall be applied in accordance with the directions of the manufacturer.
11.2 DRYING OIL CURING COATINGS: Coatings that cure by air oxidation of drying oils (e.g., alkyds, unmodified drying oils, epoxy esters, etc.) shall be applied in accordance with the preceding provisions of this specification.
11.3 VINYLS AND CHLORINATED RUBBER COAT-INGS: Where permitted by local regulations, vinyl and
chlorinated rubber finish coatings shall be applied by spray, with application by brush limited to small areas and touch-up. Primers may be brushed or sprayed. These coatings shall be thinned as recommended by the manufacturer. They shall be applied at a coverage that will result in the dry film thickness specified or, if not specified, the dry film thickness recommended by the manufacturer. When vinyl or chlorinated rubber coatings are applied by brush, coatings shall be applied to the surface with a minimum of brushing so that there is little or no lifting or softening of the undercoats.
11.4 BITUMINOUS COATINGS
11.4.1 Bituminous coating (thin film): The term bitumi-nous coating (thin film) refers to low consistency solutions of coal tar or asphalt without filler or with only a slight amount of filler. They shall be applied in the same manner as conventional coatings and shall be applied at a coverage that will result in the dry film thickness specified. The expected range of dry film thickness for these thin film bituminous coatings is from 1.7 to 3.0 mils (40 to 75 micrometers). Unless otherwise specified, the necessary number of coats shall be applied to provide a total minimum dry film thickness of 5 mils (125 micrometers).
11.4.2 Cold-applied bituminous coating (medium film): The term cold-applied bituminous coating (medium film) refers to high consistency filled solutions of coal tar or asphalt. They shall be applied by brushing or spraying. If spray applied, special heavy-duty pump type spray equipment shall be used. This material should be stirred without thinning until it attains proper consistency for application. It shall be applied at a coverage that will result in the dry film thickness specified or, if not specified, the dry film thickness as recommended by the manufacturer. The expected range of dry film thickness for the cold-applied bituminous coating (medium film) is from 5 to 10 mils (125 to 250 micrometers) per coat and unless otherwise specified, the necessary number of coats shall be applied to provide a minimum dry film thickness of 12 mils (300 micrometers).
11.4.3 Cold-applied bituminous coating (thick film): The term cold-applied bituminous coating (thick film) refers to very high consistency filled solutions of coal tar or asphalt. They shall be applied by brushing or spraying. If spray ap-plied, special heavy-duty pump type spray equipment shall be used. These materials must be stirred without thinning until they attain the proper consistency for application. They shall be applied at a coverage that will result in the dry film thickness specified or, if not specified, the dry film thickness as recommended by the manufacturer. The expected range of dry film thickness for the cold-applied bituminous coating (thick film) is from 15 to 18 mils (380 to 460 micrometers) per coat and unless otherwise specified the necessary number of coats shall be applied to provide a minimum dry film thickness of 25 mils (635 micrometers).
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11.4.4 Cold-applied bituminous mastic (extra-thick film): The term cold-applied bituminous mastic (extra-thick film) refers to very thickly applied filled solutions of coal tar or asphalt applied by brushing, troweling, or spraying. If spray applied, special heavy-duty pump type spray equipment shall be used. Thinning should not be necessary and shall not take the place of adequate stirring. They shall be applied at a cov-erage that will result in the dry film thickness specified or, if not specified, the dry film thickness as recommended by the manufacturer. The expected range of dry film thickness for the cold-applied bituminous mastic (extra-thick film) is about 35 to 65 mils (890-1650 micrometers) per coat and it is preferable that it be applied in two coats. For additional information, refer to Paints 12, 32, and 33. A minimum total dry film thickness of 70 mils (1780 micrometers) is suggested.
11.4.5 Bituminous emulsion: The term “bituminous emulsion” refers to high consistency filled emulsions of coal tar or asphalt and water. Since they are compounded with water they must not be permitted to freeze at any time before drying. These emulsions shall be applied by brushing, spraying, or troweling. If spray applied, special heavy-duty pump type spray equipment shall be used. Thinning should not be necessary and shall not take the place of adequate stirring. They shall be applied at a coverage that will result in the dry film thickness specified or, if not specified, the dry film thickness as recom-mended by the manufacturer. The expected range of dry film thickness for the bituminous emulsion is from 8 to 15 mils (200 to 380 micrometers) per coat and unless otherwise specified the necessary number of coats shall be applied to provide a minimum dry film thickness of 20 mils (500 micrometers).
11.4.6 Coal tar primer and enamel: Coal tar primer and enamel for the interior and exterior of steel pipe, tanks and hydraulic structures shall be applied in accordance with the requirements of American Water Works Association (AWWA) specification C-203 unless otherwise specified. This specifi-cation is not intended to cover application of coal tar primers and enamel to steel structures of oil and gas pipelines when a low penetration enamel is considered desirable. Such ap-plication shall be done in accordance with specifications of the purchaser.
11.5 EPOXY AND COAL TAR EPOXY COATINGS: Two-package chemically cured epoxy and coal tar epoxy coatings shall be stored, mixed, thinned, applied, and cured in accordance with the manufacturerʼs instructions and with the provisions of Sections 5.4.11 and 6. Also, any special precautions and instructions by the manufacturer shall be followed. Chemically cured coatings shall not be applied when the surface, coating, or air temperature is below the manufacturerʼs published minimum recommendation. When coatings formulated for low temperature application are applied at temperatures below 40 °F (4° C), it shall be verified that the
surface is free of moisture (unless formulation permits it) and ice at the time of application.
11.6 ZINC-RICH COATINGS: For additional information refer also to SSPC Paint 20, “Zinc-Rich Primers” and PS Guide 12.00, “Guide to Zinc-Rich Coating Systems.”
11.6.1 Inorganic zinc-rich: Inorganic zinc-rich coatings shall be applied by spray. Application by brush shall be limited to small areas and touch-up work. If the zinc powder is pack-aged separately, mix with the vehicle just before use. Inorganic zincs shall be thinned as recommended by the manufacturer. The coatings shall be applied to a dry film thickness between 2 to 4 mils (50 and 100 micrometers), unless otherwise stated in the specification or manu-facturerʼs written instructions. When applying by spray, the zinc dust shall be kept in sus-pension by use of a mechanical agitator for both airless and air atomized (conventional) spray. The vessel containing the coating and the spray gun shall be kept at approximately the same elevation (e.g., within 3 feet [1 meter]) while spraying. Prior to topcoating, a barrier or tie coat may be required for overcoating with certain generic coatings. The manufacturerʼs recommendations shall be followed. Sufficient curing of the zinc-rich primer is necessary before topcoating. The coating manufacturer may require a minimum relative humidity to ensure curing. Dry spray of the zinc-rich primer will result in improper adhesion of the topcoat. Dry spray shall be removed with a stiff bristle brush or wire screen without polishing the surface of the coating.
11.6.2 Organic zinc-rich: Most of the provisions of Sec-tion 11.6.1 are also applicable for the application of organic zinc-rich coatings except that they may also be applied by brush or roller when permitted by the manufacturerʼs written recommendations.
11.7 URETHANE COATINGS: For additional information, refer also to PS Guide 17.00, “Guide for Selecting Urethane Coating Systems.”
11.7.1 Single component moisture cured urethane coat-ings which meet ASTM D 16, Type II may be applied by brush, roller, conventional spray, and airless spray. Special care shall be taken to ensure that all spray equipment is moisture free. Since these coatings cure by reaction with moisture in the air, it should be noted that application on days when the humidity is low will result in slow cure. The manufacturerʼs directions shall be followed concerning thinning and application parameters. Type II urethane coatings shall be mixed by a mechanical mixer prior to application. This shall be done slowly so as not to create a vortex and introduce moisture into the coating which could reduce the pot life.
11.7.2 Two component polyisocyanate polyol-cured urethane coatings may be applied by brush, roller, conventional
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free. The manufacturerʼs directions shall be followed concerning thinning and application parameters. The two components (isocyanate and polyol) shall be mixed as specified by the manufacturer. Mixing shall be done slowly so as not to create a vortex and introduce moisture into the coating which could reduce the pot life. These urethane coatings are extremely susceptible to moisture contamination and shall not be applied unless temperatures, both during application and up to three hours after application, will be at least 5 F° (3 C°) above the dew point.
11.8 WATERBORNE THERMOPLASTIC COATINGS
11.8.1 Waterborne thermoplastic coatings (commonly called “latex coatings”) may be applied by spray, brush, or roller. Cross brushing or cross spraying application is highly desirable. Application by spray tends to provide the best leveling. Conventional or airless spray can be used with most latex coatings. Since one-coat systems have very limited protective properties, multiple-coat systems shall always be applied. On structural steel, the preferred system is two coats of primer and one or more topcoats to achieve the specified dry film thickness. Where the dry film thickness is not speci-fied, apply each coat at a minimum dry film thickness of 2.5 mils (64 micrometers) to achieve a total dry film thickness of 7.5 mils (190 micrometers). For additional information, refer to SSPC Paints 23 and 24.
11.8.2 The atmospheric conditions at the time the latex coating, especially the primer, is applied are extremely im-portant. A latex primer shall not be applied at a temperature below 50 °F (10 °C) or above 120 °F (50 °C) or when curing (coalescence) is expected outside this range. It should be noted that some waterborne thermoplastic coatings are formulated for application at temperatures below 50 °F (10 °C). High humidities (e.g., 80%) will slow the drying of these coatings (see Sections 6.2 and 6.3).
11.8.3 The best conditions for storage of latex coatings are at temperatures between 40 °F (4 °C), and 80 °F (27 °C).
12. Curing and Handling of Coatings
12.1 DRYING OF COATINGS
12.1.1 The minimum and maximum curing times before overcoating an existing coat of coating shall conform to the primer and overcoat manufacturerʼs written recoat instructions. If the maximum time is exceeded, the cured coating shall be roughened or otherwise treated as recommended by the manu-facturer of the overcoat before applying another coat.
12.1.2 No coating shall be force dried under conditions which will cause checking, wrinkling, blistering, formation of pores, or detrimentally affect the protective properties of the
coating. Always check with the coating manufacturer before force drying a coating.
12.1.3 Coating shall be protected from rain, condensation, contamination, snow, and freezing until sufficiently cured for exterior exposure.
12.1.4 No coating shall be subjected to immersion be-fore it is thoroughly dried or cured in accordance with the manufacturerʼs written instructions.
12.2 HANDLING OF COATED STEEL
12.2.1 Coated steel shall not be handled, loaded for ship-ment, or shipped until the coating has dried except as necessary in turning for coating or stacking for drying.
12.2.2 Coating which is damaged in handling shall be removed and touched up with the same number of coats and kinds of coatings as were previously applied to the steel or as specified by the procurement documents
13. Inspection
13.1 Unless otherwise specified in the procurement docu-ments, the contractor or material supplier is responsible for quality control to assure that the requirements of this document are met. Work and materials supplied under this standard are also subject to inspection by the purchaser or an authorized representative. Materials and work areas shall be accessible to the inspector
13.2 Conditions not complying with this standard shall be corrected. In the case of a dispute, an arbitration or settlement procedure established in the procurement documents (project specification) shall be followed. If no arbitration or settlement procedure is established, then a procedure mutually agree-able to purchaser and material supplier (or contractor) shall be used.
14. Safety and Environmental Concerns
14.1 All safety and environmental requirements stated in this specification and its component parts apply in addition to any applicable federal, state, and local rules and requirements. They also shall be in accord with instructions of the coating manufacturer and requirements of insurance underwriters.
14.2 Coatings may be hazardous because of their flam-mability or toxicity. Proper safety precautions shall be observed to protect against these recognized hazards. Safe handling practices are required and should include, but not be limited to, the provisions of PA Guide 3, “A Guide to Safety in Coating Application.”
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14.3 Some coatings specified herein may not comply with some air quality regulations because of their organic solvent content.
14.4 MATERIAL SAFETY DATA SHEETS (MSDSs): Information pertaining to the safe handling, application, and disposal of coatings can be obtained from their MSDSs, which are supplied by the manufacturers. The MSDSs for all materials shall accompany them wherever they are stored or used.
15. Disclaimer
15.1 While every precaution is taken to ensure that all information furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, coatings, or methods specified herein, or of the specification or standard itself.
15.2 This specification does not attempt to address prob-lems concerning safety associated with its use. The user of this specification, as well as the user of all products or practices described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.
16. Notes
Notes are not requirements of this specification.
16.1 It is recommended that coating be stored in a warm building during very cold weather so that it is not necessary to thin the coating excessively for application since excessive thinning will result in a low solids content, and the dry film thickness will be below that intended for the particular mate-rial. It is advantageous to the contractor that this material be kept warm or heated prior to use, inasmuch as less material will be required, application will be easier, and the resulting film will meet the intent of the specification. When warming coatings, their temperature should not be permitted to exceed 100 °F (38 °C) unless special coating heating equipment is used. When the coating (or thinner) has a flash point below 100 °F (38 °C) it should not be heated above its flash point if it is heated in an open container.
16.2 As much care as deemed practical should be exercised to prevent contamination of coated surfaces with particulate materials, soluble salts, and other foreign matter before over-coating. Thus, overcoating should be accomplished as soon as possible after curing requirements of undercoats are met. When intercoat contamination occurs before overcoating, the surface shall be washed with water and detergent or other approved material to remove as many contaminants as possible.
16.3 A number of instruments are available that measure temperature with great accuracy. Some are described in The
Inspection of Coatings and Linings. Also refer to Volume 1 of the SSPC Painting Manual.
16.4 Cold weather, high humidity, water, fog and mist, and rain during coating application, drying, or curing are detrimental to the performance of most coatings. It is impossible to set down specific rules which govern the limits in which the coating application should be done since the variation from one coat-ing to another may be large. Generally speaking, application should be done only under conditions which are conducive to quick evaporation of water. This generally means that the relative humidity should be low. Steel should not be coated when it is below the dew point since condensation of water on the steel will result. The only exception is for coatings to be applied that are formulated to tolerate moisture or liquid water on the surface.
Coatings which dry solely by evaporation of organic solvent are not believed to be harmed by application to steel which is below 32 °F (0 °C); however, under such conditions, the danger always exists that there will be a layer of ice on the surface of the steel. This same condition may prevail for application of conventional, air-oxidizing coatings. When the humidity is low and the steel is thoroughly dry beyond question, it is believed that coatings may be applied, provided the coating is of a type which will not be injured or whose drying will not be impaired by low temperature or low humidity.
Generally speaking, coatings should not be applied in weather which will subject them to damage, nor should they be applied when it is expected that the temperature will vary either below or above the temperature range recommended in writing by the manufacturer or drop to freezing before they have cured.
The dew point (see Section 6.2) is the temperature be-low which moisture from the air will begin to condense. If the surface temperature of the substrate is at or below the dew point, moisture will condense on it. It may be determined with a sling psychrometer, or other instrument, usually requiring determination of wet and dry bulb temperatures (ASTM E 337, “Relative Humidity by Wet- and Dry-Bulb Psychrom-eter”). Hand-held, digital moisture meters, hygrometers, etc., can make measurement of relative humidity and dew point simple and instantaneous. These electronic instruments can also provide simple measurement of relative humidity and dew point of a surface that is at a different temperature than ambient conditions.
In practice, the dew point requirement can be presumed to be satisfied if a thin, clearly defined film of water applied to the cleaned surface with a damp cloth evaporates within 15 minutes.
Low temperatures greatly reduce the curing rates of chemi-cally cured coatings (certain epoxies, urethanes, inorganic zinc-rich coatings, coal tar epoxies, etc.). Unless otherwise permitted, chemically cured coatings should not be applied when the surface, coating, or ambient temperature is outside the range recommended by the coating manufacturerʼs writ-ten instructions.
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16.5 Coatings on structural steel are generally applied by brush or by spray. Either method is satisfactory if properly performed and the coating is formulated for the application method being used. The variations are slight, and often over-shadowed by variations in workmanship.
Brushing of primers has the advantage of working coat-ing into cracks and crevices and other surface irregularities. It may create brush marks, however, with coatings having limited leveling. Lacquer type coatings, such as vinyls, may be applied by brush with considerable difficulty only; the prim-ing coat brushes on with least difficulty and results in better adhesion to the surface than spraying. Finish coats of lacquer type coating tend to lift underlying coats by solvent action and brushing combined; for this reason such finish coatings are best applied by spraying.
With many types of coatings, properly used high pressure spray methods can result in a thicker, more impermeable film. Spray operators must be properly selected and trained. Careful supervision and inspection are necessary with the various spray application methods to insure against such difficulties as dirty surfaces, dry spray, pinholes, holidays, missed areas, blind spots, contamination of coating or air, wind loss, or excessive outdoor overspray.
Several advantages are possible with the various high pressure airless methods of coating application, both hot and cold spray. These include labor savings as a result of fast ap-plication and a greater thickness per coat. Additional savings also can be traced to less flowback, less overspray, power (compressor) savings, use of higher solids in coating formula-tions, and less sensitivity to changes in ambient temperature during application.
16.6 With roller application of coating on structural steel, high production rates approaching that of conventional spraying may be possible. The method works best on large smooth areas such as tanks or walls. Difficulties may be encountered when coating welds, rough spots, pits, rivet heads, edges, corners, etc., to ensure that adequate coating is applied. Supplementary brush coating is mandatory for those areas on structural steel, even though special rollers for these areas are available for general work. The requirements are generally the same as for brush and spray coating. Excellent results have been achieved, and it is possible to build up specified film thicknesses by this method. Roller coating is particularly useful where spraying cannot be undertaken due to the hazards from overspray or the flammability of solvent.
16.7 Selection for the type of shop primer to be used should take into consideration the length of time anticipated between the shop applied coat and the first coat applied in the field. The period before a shop coat is to be topcoated in the field can vary from the construction schedule. Long periods of field exposure may degrade the shop coating so that it may have to receive periodic maintenance to continue to protect the steel from corrosion and be in a suitable condi-tion for overcoating.
When longer periods of exposure are anticipated, special consideration should be given to surface preparation, coating selection, film thickness, and to early application of a second primer/overcoat. Between shop priming and field coating, structural steel is often exposed to the most severe environ-ments it will ever encounter and at a time when it is protected by only one coat of primer. The prime coat of coating is usually formulated to provide short-term protection and a good bond between the steel substrate and subsequent coats. Many shop-applied primers are not intended to provide long-term protection of the steel, particularly during exposure to damp-ness, bad weather, and industrial fumes.
16.8 For high-performance coating service, special weld surfacing may be required to provide suitable surface conditions for the coating system specified. NACE RP0178 provides one method of specifying weld surfacing requirements, as well as other design and fabrication requirements for improving coat-ing serviceability. Other methods of specifying and accepting weld surfacing conditions are employed in various industries. The weld surfacing requirements should generally be placed in the project specifications so that the painting contractor will not have to perform welding or grinding to provide the specified final surface conditions.
16.9 In maintenance coating it is not ordinarily intended that sound, adherent, old coating be removed unless it is excessively thick or brittle or is incompatible with the new coating. It is essential, however, that the removal of deterio-rated coating be carried back around the edges of the spot or area until an area of completely intact and adherent coating film, with no rust or blisters underneath, is attained. Edges of tightly adherent coating remaining around the area to be recoated must be feathered so that the recoated surface can have a smooth appearance to provide a transition from the area of repair to the intact coating. The remaining old coating should have sufficient adhesion so that it cannot be lifted as a layer by inserting the blade of a dull putty knife under it using moderate pressure.
Unless experience or spot tests have shown otherwise, it is usually preferable to use the same generic type of coating in recoating as in the original coating. If the new coating curls or lifts after application to an existing coating, the cleaning and application procedures should be reviewed to determine if good coating practices have been followed. If the new coating is found to be incompatible with the previous coating system, either the primer should be replaced with one more compat-ible, or the old coating should be completely removed before application of a new system.
Coating records should be kept by the owner for the pur-pose of determining information on the durability of coatings and the economic protection afforded by them. Refer to Volume 1 of the SSPC Painting Manual for additional information and a suggested record form.
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APPENDIX A - ADDITIONAL REFERENCE MATERIALS
The standards, reports, and publications listed below are not required as part of the specification but are recommended resources (note that the standards listed in Section 3 are required parts of this specification).
SSPC PUBLICATIONS AND STANDARDS: AB 1 Mineral and Slag AbrasivesAB 2 Cleanliness of Recycled Ferrous
Metallic AbrasivesAB 3 Ferrous Metallic Abrasives PA 1 Shop, Field, and Maintenance
Painting of SteelPA Guide 4 Guide to Maintenance Recoating
with Oil Base or Alkyd Coating Systems
PA Guide 5 Guide to Maintenance Coating Programs
Guide 6 Guide for Containing Debris Generated During Paint Removal Operations
Guide 7 Guide for the Disposal of Lead-Contaminated Surface Preparation Debris
Guide 8 Guide to Topcoating Zinc-Rich Primers
Guide 11 Guide for Coating ConcreteGuide 12 Guide of the Illumination of Indus-
trial Painting ProductsME 1 Test Panel Preparation Method No.
1, Uncontaminated Rusted SteelPaint 15 Steel Joist Shop PrimerPaint 20 Zinc Rich Primers (Type I - “Inor-
ganic” and Type II - “Organic”)Paint 23 Latex Primer for Steel SurfacesPaint 24 Latex Semi-Gloss Exterior TopcoatPaint 25 Zinc Oxide, Alkyd, Linseed Oil
Primer for Use Over Hand Cleaned Steel
Paint 25 BCS Zinc Oxide, Alkyd, Linseed Oil Primer for Use Over Blast Cleaned Steel
Paint 32 Coal Tar Emulsion CoatingPaint 33 Coal Tar Mastic - Cold-AppliedPaint 34 Water-Borne Epoxy Topcoat for
Steel StructuresPaint 35 Medium Oil Alkyd Primer (Air Dry/
Low Bake)PS Guide 17.00 Guide for Selecting Urethane
Painting SystemsPS Guide 12.00 Guide to Zinc-Rich Coating Systems
QP 1 Standard Procedure for Evaluating Painting Contractors (Field Ap-plication to Complex Industrial Structures)
QP 3 Standard Procedure for Evaluating Qualifications of Shop Painting Contractors
SP 2 Hand Tool CleaningSP 3 Power Tool CleaningSP 5/NACE No. 1 White Metal Blast CleaningSP 6/NACE No. 3 Commercial Blast CleaningSP 7/NACE No. 4 Brush-Off Blast CleaningSP 10/NACE No. 2 Near-White Blast CleaningSP 11 Power Tool Cleaning to Bare MetalSP 12/NACE No. 5 Surface Preparation and Cleaning
of Metals by Water Jetting Prior to Recoating
SP 13/NACE No. 6 Surface Preparation of ConcreteSP 14/NACE No. 8 Industrial Blast CleaningTR 2/NACE 6G198 Joint Technical Report, Wet Abrasive
Blast CleaningTU 1 Surface-Tolerant Coatings for
SteelTU 2 Design, Installation, and Main-
tenance of Coating Systems for Concrete Used in Secondary Containment Facilities
TU 3 Technology Update on Ovecoating TU 4 Field Methods for Retrieval and
Analysis of Soluble Salts on Substrates
VIS 1 Guide and Reference Photographs for Steel Surfaces Prepared by Dry Abrasive Blast Cleaning
VIS 3 Guide and Reference Photographs for Steel Surfaces Prepared by Hand and Power Tool Cleaning
VIS 4/NACE No. 7 Guide and Reference Photographs for Surfaces Cleaned by Waterjetting
SSPC 97-07 The Inspection of Coatings and Linings
ASTM STANDARD:E 337 Standard Test Method for Measur-
ing Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
AMERICAN WATER WORKS ASSOCIATION (AWWA) STANDARD:
C 203 Coal-Tar Protective Coatings and Linings for Steel Water Pipelines - Enamel and Tape - Hot Applied
SSPC-PA 2May 1, 2012
1
SSPC: THE SOCIETY FOR PROTECTIVE COATINGSCOATING APPLICATION STANDARD NO. 2PROCEDURE FOR DETERMINING CONFORMANCE TO
DRY COATING THICKNESS REQUIREMENTS
1.6 This standard is not intended to be used for measure-ment of thermal spray coatings. The thickness measurement procedures for these coatings are described in SSPC-CS 23.002.
2. Referenced Standards
2.1 The latest issue, revision, or amendment of the refer-enced standards in effect on the date of invitation to bid shall govern unless otherwise specified. Standards marked with an asterisk (*) are referenced only in the Notes, which are not requirements of this standard.
2.2 If there is a conflict between the requirements of any of the cited reference standards and this standard, the require-ments of this standard shall prevail.
2.3 ASTM International Standard3
D 7091 Standard Practice for Nondestructive Measure-ment of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals (mandatory document)
2.4 SSPC: The Society for Protective Coatings Standard:
* PA Guide 11 Protecting Edges, Crevices, and Irreg-ular Steel Surfaces by Stripe Coating
3. DEFINITIONS
3.1 Gage Reading: A single instrument reading.
3.2 Spot Measurement: The average of three, or at least three gage readings made within a 1.5-inch (approximately 4-centimeter [~4-cm]) diameter circle. Acquisition of more than three gage readings within a spot is permitted. Any unusually
2 CS 23.00/AWS C2.23M/NACE No. 12, Specification for the Applica-tion of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and Their Alloys and Composites for the Corrosion Protection of Steel is available online at <http://www.sspc.org/marketplace>
3 ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [email protected]. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.
1. Scope
1.1 This standard describes a procedure for determining shop or field conformance to a specified coating dry film thick-ness (DFT) range on ferrous and non-ferrous metal substrates using nondestructive coating thickness gages (magnetic and electronic) described in ASTM D 7091.
1.2 The procedures for adjustment and measurement acquisition for two types of gages: “magnetic pull-off” (Type 1) and “electronic” (Type 2) are described in ASTM D 7091.
1.3 This standard defines a procedure to determine whether dry coatings conform to the minimum and the maximum thickness specified. See Note 11.1 for an example of a possible modification when measuring dry film thickness on overcoated surfaces.
1.4 This document is not intended to prescribe a frequency of coating thickness measurement for a coating failure investigation1.
1.5 This document contains the following non-mandatory appendices:
Appendix 1 - Numerical Example of Average Thickness
MeasurementAppendix 2 - Methods for Measuring Dry Film Thickness
on Steel Beams (Girders)Appendix 3 - Methods for Measuring Dry Film Thickness
for a Laydown of Beams, Structural Steel, and Miscellaneous Parts after Shop Coating
Appendix 4 - Method for Measuring Dry Film Thickness on Coated Steel Test Panels
Appendix 5 - Method for Measuring Dry Film Thickness of Thin Coatings on Coated Steel Test Panels that Have Been Abrasive Blast Cleaned
Appendix 6 – Method for Measuring the Dry Film Thick-ness of Coatings on Edges
Appendix 7 – Method for Measuring Dry Film Thickness on Coated Steel Pipe Exterior
Appendix 8 – Examples of the Adjustment of Type 2 Gages Using Shims
1 The number and location of measurements during a coating failure investigation may be more or less frequent than described by this standard.
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high or low gage readings that are not repeated consistently are discarded. The average of the acceptable gage readings is the spot measurement.
3.3 Area Measurement: The average of five spot measurements obtained over each 100 ft2 (~10 m2) of coated surface.
4. Description of Gages
4.1 Gage Types: The gage type is determined by the operating principal employed in measuring the thickness and is not determined by the mode of data readout, i.e. digital or analog.
4.1.1 Type 1 – Magnetic Pull-Off Gages: In magnetic pull-off gages, a permanent magnet is brought into direct contact with the coated surface. The force necessary to pull the magnet from the surface is measured and interpreted as the coating thickness value on a scale or display on the gage. Less force is required to remove the magnet from a thick coating. The scale is nonlinear.
4.1.2 Type 2 – Electronic Gages: An electronic gage uses electronic circuitry to convert a reference signal into coating thickness.
5. Calibration and Verification of Accuracy
5.1 ASTM D 7091 describes three operational steps necessary to ensure accurate coating thickness measurement: calibration, verification and adjustment of coating thickness measuring gages, as well as proper methods for obtaining coating thickness measurements on both ferrous and non-ferrous metal substrates. These steps shall be completed before taking coating thickness measurements to determine conformance to a specified coating thickness range.
5.2 Gages shall be calibrated by the manufacturer or a qualified laboratory. A Certificate of Calibration or other documentation showing traceability to a national metrology institution is required. There is no standard time interval for re-calibration, nor is one absolutely required. Calibration inter-vals are usually established based upon experience and the work environment. A one-year calibration interval is a typical starting point suggested by gage manufacturers.
5.3 To guard against measuring with an inaccurate gage, gage accuracy shall be verified at a minimum of the begin-ning and end of each work shift according to the procedures described in ASTM D 7091. The user is advised to verify gage accuracy during measurement acquisition (e.g., hourly) when a large number of measurements are being obtained. If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy shall be rechecked.
5.4 Record the serial number of the gage, the reference
standard used, the stated thickness of the reference standard
as well as the measured thickness value obtained, and the method used to verify gage accuracy. If the same gage, refer-ence standard, and method of verification are used throughout a job, they need to be recorded only once. The stated value of the standard and the measured value must be recorded each time accuracy is verified.
5.5 If the gage fails the post-measurement accuracy verification check, all measurements acquired since the last accuracy verification check are suspect. In the event of physical damage, wear, or high usage, or after an established calibration interval, the gage shall be rechecked for accuracy of measurement. If the gage is not measuring accurately, it shall not be used until it is repaired and/or recalibrated (usually by the gage manufacturer).
5.6 Type 1 gages have nonlinear scales and any adjusting feature is linear in nature. Any adjustment of these gages will limit the DFT range for which the gage will provide accurate readings; therefore adjustment of the gage is not recom-mended. Furthermore, the application of a single “correction value” representing the full range of the gage to compensate for a gage that is not measuring accurately is not appropriate, since the correction will also be non-linear.4
6. Measurement Procedure - Type 1 Gages
6.1 Type 1 gage accuracy is verified using smooth test blocks. In order to compensate for any effect of the substrate itself and surface roughness, obtain measurements from the bare, prepared substrate at a minimum of ten (10) locations (arbitrarily spaced) and calculate the average value. This value represents the effect of the substrate/surface roughness on a coating thickness gage. This average value is the base metal reading (BMR). The gage shall not be adjusted to read zero on the prepared, bare substrate.
6.2 Measure the DFT of the dry coating at the number of spots specified in Section 8.
6.3 Subtract the BMR from the gage reading to obtain the thickness of the coating.
7. MEASUREMENT PROCEDURE - TYPE 2 GAGES
7.1 The manufacturers of Type 2 (electronic) gages prescribe different methods of adjustment to measure dry film thickness over abrasive blast cleaned surfaces. Adjust the gage according to the manufacturers instructions using one of the methods described in ASTM D 7091 or Appendix 8 of this standard.
4 A correction curve can be prepared by plotting the actual gage readings against the stated values on the calibration test blocks. Subsequent coating thickness measurements can be “corrected” by plotting the measurements along the correction curve. The correc-tion curve may or may not cover the full range of the gage, but should cover the intended range of use. The Base Metal Readings (BMR) described in 6.1 may also need to be plotted on the correction curve.
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7.2 Measure the DFT of the dry coating at the number of spots specified in Section 8.
8. Required Number of Measurements for Conformance to a Thickness Specification
8.1 Number of Measurements: Repeated gage read-ings, even at points close together, often differ due to small surface irregularities of the coating and the substrate. There-fore, a minimum of three (3) gage readings shall be made for each spot measurement of the coating. For each new gage reading, move the probe to a new location within the 1.5 inch (4-cm) diameter circle defining the spot. Discard any unusually high or low gage readings that are not repeated consistently. The average of the acceptable gage readings is the spot measurement.
8.2 Unless otherwise specified in the procurement docu-ments (project specification), an area measurement is obtained by taking five (5) separate spot measurements (average of the gage readings described in 8.1) randomly spaced throughout each 100 ft2 (~10-m2) area to be measured and representative of the coated surface. The five spot measurements shall be made for each 100 ft2 (~10-m2) of area as follows:
8.2.1 For areas of coating not exceeding 300 ft2 (~30 m2) arbitrarily select and measure each 100 ft2 (~10-m2) area.
8.2.2 For areas of coating greater than 300 ft2 (~30 m2) and not exceeding 1,000 ft2 (~100 m2), arbitrarily select and measure three 100 ft2 (~10-m2) areas.
8.2.3 For areas of coating exceeding 1,000 ft2 (~100 m2), arbitrarily select and measure the first 100 m2 (~1,000 ft2) as stated in Section 8.2.2. For each additional 1,000 ft2 (~100 m2) coated area (or increment thereof), arbitrarily select and measure one additional 100 ft2 (~10-m2) area.
8.2.4 If the coating thickness for any 100 ft2 (~10-m2) area is not in compliance with the contract documents, the procedure described below shall be followed to assess the magnitude of the nonconforming thickness.
8.2.4.1 Determine the spot DFT at 5-ft (1.5-m) intervals in eight equally spaced directions radiating outward from the nonconforming 100 ft2 (~10-m2) area as shown in Figure 1.
If there is no place to measure in a given direction, then no measurement in that direction is necessary. Acquire spot measurements in each direction (up to the maximum surface area coated during the work shift) until two consecutive conforming spot measurements are acquired in that direction or until no additional measurements can be made. Accept-able spot measurements are defined by the minimum and maximum values in the contract documents. No allowance is made for variant spot measurements as is the practice when determining the area DFT.
8.2.4.1.1 On complex structures or in other cases where making multiple spot measurements at 5-ft (1.5-m) intervals is not practical, single spot measurements shall be performed on repeating structural units or elements of structural units. This method shall be used when the largest dimension of the unit is less than 10 ft (3 m). Make single spot measurements on repeating structural units or elements of structural units until spot measurements on two consecutive units in each direction are conforming or until there are no more units to test.
8.2.4.2 Non-compliant areas shall be demarcated using removable chalk or other specified marking material and docu-mented. All of the area within 5 ft (1.5 m) of any non-compliant spot measurement shall be designated as non-compliant. For a given measurement direction or unit measurement, any compliant area or unit preceding a non-compliant area or unit shall be designated as suspect, and as such is subject to re-inspection after corrective measures are performed.
8.2.5 Appendices 2 through 7 provide specifiers with optional alternatives for defining the area size as well as the number and frequency of spot measurements to include in project specifications as appropriate for the size and shape of the item or structure to be coated.
9. Conformance to Specified Thickness
9.1 A minimum and a maximum thickness are normally specified for each layer of coating. If a single thickness value is specified and the coating manufacturer does not provide a recommended range of thickness, then the minimum and maximum thickness for each coating layer shall be +/- 20% of the stated value.
9.2 Table 1 provides five thickness restriction levels. Level 1 is the most restrictive and does not allow for any deviation of spot or area measurements from the specified minimum and maximum thickness, while Level 5 is the least restrictive. Depending on the coating type and the prevailing service envi-ronment, the specifier selects the dry film thickness restriction level for a given project. If no restriction level is specified, then Level 3 is the default. It is possible to specify a maximum thick-ness threshold for Level 5 Spot or Area measurements for some generic product types and service environments.
9.3 For the purpose of final acceptance of the total dry film thickness, the cumulative thickness of all coating layers
NONCONFORMING
AREA
FIGURE 1RADIATING SPOT MEASUREMENTS TO DETERMINE
EXTENT OF NONCONFORMING AREA
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shall be no less than the cumulative minimum specified thick-ness and no greater than the cumulative maximum specified thickness.
10. Disclaimer
10.1 While every precaution is taken to ensure that all information furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, coatings or methods specified therein, or of the specification or standard itself.
10.2 This standard does not attempt to address prob-lems concerning safety associated with its use. The user of this standard, as well as the user of all products or practices described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.
11. Notes
Notes are not requirements of this standard.
11.1 Overcoating: Maintenance painting often involves application of a new coating over an existing coating system. It can be very difficult to accurately measure the DFT of this newly applied coating using non-destructive methods. First, access to the profile is not available, compromising the accu-racy of the BMR or the adjustment of a Type 2 gage. Second, unevenness in the DFT of the existing coating necessitates careful mapping of the “before and after” DFT readings. This unevenness also adds to the statistical variation in trying to establish a base DFT reading to be subtracted from the final DFT.
A paint inspection gage (sometimes called a Tooke or PIG gage) will give accurate DFT measurements, but it requires that an incision be made through the coating (overcoat only or total system), so each measurement site will require repair.
A practical approach to monitoring DFT (when overcoating) is to compute the DFT using wet film thickness (WFT) read-ings, the percent volume solids of the coating being applied, and any thinner addition as shown below.
DFT = Measured WFT x % Volume Solids, or
DFT = Measured WFT x % volume solids ÷ (100% + % thinner added)
If the DFT of the existing coating is not too uneven or
eroded, the average DFT of the existing coating can be measured per this standard to establish a base DFT. This base DFT can then be subtracted from the total DFT to isolate the thickness of the overcoat(s).
11.2 Correcting for Low or High Thickness: The speci-fier should specifically state the methodology to correct the applied dry film for low or high thickness. If this information is not contained in the specification, then the manufacturer’s instructions should be followed.
APPENDIX 1 - Numerical Example of Average Thickness Measurement
Appendix 1 is not a mandatory part of this standard.
The following numerical example is presented as an illus-tration of Section 8. Metric values are calculated equivalents from U.S. Customary measurements (reference Journal of Protective Coatings and Linings, Vol. 4, No 5, May 1987). The example is based on a Level 3 Restriction (default).
TABLE 1COATING THICKNESS RESTRICTION LEVELS
Thickness Gage Reading SpotMeasurement Area Measurement
Level 1Minimum Unrestricted As specified As specifiedMaximum Unrestricted As specified As specifiedLevel 2Minimum Unrestricted As specified As specifiedMaximum Unrestricted 120% of maximum As specifiedLevel 3Minimum Unrestricted 80% of minimum As specifiedMaximum Unrestricted 120% of maximum As specifiedLevel 4Minimum Unrestricted 80% of minimum As specifiedMaximum Unrestricted 150% of maximum As specifiedLevel 5Minimum Unrestricted 80% of minimum As specifiedMaximum Unrestricted Unrestricted Unrestricted
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Suppose this structure is 300 ft2 (~30 m2) in area. Mentally divide the surface into three equal parts, each being about 100 ft2 (~10 m2).
Part A - 100 ft2 (~10 m2) Part B - 100 ft2 (~10 m2)Part C - 100 ft2 (~10 m2)
First, measure the coating thickness on Part A. This involves at least 15 gage readings with a Type 1 or Type 2 device (see Figure A1). Assume the specification calls for 2.5 mils (~64 micrometers [µm]) minimum thickness. The coating thickness for area A is then the average of the five spot measurements made on area A, namely 2.6 mils (65.4 µm).
Spot 1 2.5 mils 64 µmSpot 2 3.0 76 Spot 3 2.1 53 Spot 4 3.0 76Spot 5 2.3 58 Average 2.6 mils 65.4 µm
Considering the U.S. Customary Measurements: The average, 2.6 mils, exceeds the specified minimum of 2.5 mils and thus satisfies the specification. Next, determine if the lowest spot measurement, 2.1 mils, is within 80% of the
specified minimum thickness. Eighty percent of 2.5 mils is 2.0 mils (0.80 x 2.5 = 2.0). Although 2.1 mils is below the specified minimum, it is still within 80 percent of it, so the specification is satisfied. There are individual gage readings of 1.5 mils at Spot 5 and 1.8 mils at Spot 3, both of which are clearly less than 2.0 mils. This is allowed because only the average of the three readings (i.e. the spot measurement) must be greater than or equal to 2.0 mils.
Considering Equivalent Metric Measurements: The average, 65.4 µm, exceeds the specified minimum of 64 µm and thus satisfies the specification. Next, determine if the lowest spot measurement, 53 µm, is within 80% of the speci-fied minimum thickness. Eighty percent of 64 µm is 51 µm (0.80 x 64 = 51). Although 53 µm is below the specified minimum, it is still within 80% of it so the specification is satisfied. There are individual gage readings of 38 µm (1.5 mils) at spot 5 and 46 µm (1.8 mils) at spot 3, both of which are clearly less than 51 µm. This is allowed because only the average of the three readings (i.e., the spot measurement) must be greater than or equal to 51 µm.
Since the structure used in this example is 300 ft2 (approximately 30 m2), the procedure used to measure the film thickness of part A must be applied to both part B and part C. The measured thickness of part B must exceed the (64 µm) specified minimum, as must the thickness of part C.
FIGURE A1 PART “A” OF STRUCTURE
(AREA 100 FT2 [APPROXIMATELY 10 M2])
10 ft
10 ft Part “B”
Spot 1 2.6 3.0 2.0 Avg. 2.5
1.5 inch 1.8 2.2 2.3 Avg. 2.1
Spot 3
3.6 2.6 2.7 Avg. 3.0
Spot 2
Spot 4 2.6 3.2 3.1 Avg. 3.0
Spot 5 1.5 2.8 2.6 Avg. 2.3
GAGE READINGS
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To monitor the thickness of this entire 300-ft2 (approxi-mately 30-m2), structure, at least 45 individual gage readings must be taken, from which 15 spot measurements are calcu-lated. The five spot measurements from each 100 ft2 (10-m2) part of the structure are used to calculate the thickness of that part.
APPENDIX 2 - Methods for Measuring Dry Film Thickness on Steel Beams (Girders)
Appendix 2 is not a mandatory part of this standard, but it provides two sample protocols for measuring DFT on beams and girders.
A2.1 A challenge for the painter in coating steel beams or girders is providing the same uniform thickness over high and low vertical surfaces as over horizontal surfaces. On a beam, there are proportionately more edges that tend to have low dry film thickness (DFT) and inside corners that tend to have high DFT compared to the center of the flat surfaces. Each painter usually develops a pattern of work for a specific task. Hence, the DFT on the underside of the top flange, for example, may be consistently on the high side or the low side of the target DFT. This type of error is easy to detect and correct. Random errors pose a more difficult problem. Gross errors where the paint is obviously too thin or too thick must be corrected and are beyond the scope of this standard.
The number of spot measurements in these protocols may far exceed the “5 spot measurement per 100 ft2 (10 m2)” required in the standard. The full DFT determination, described in Section A3.2, provides a very thorough inspection of the beam. The sample DFT determination, described in Section
A3.4, allows for fewer spot measurements. The user does not have to require a full DFT determination for every beam in the structure. For example, the requirement may be for a full DFT determination on one beam out of ten, or a sample DFT deter-mination on one beam out of five, or a combination of full and sample DFT determinations. Note that for existing structures, the top side of the top flange (Surface 1) may not be accessible for measuring coating thickness.
A beam has twelve different surfaces as shown in Figure A2. Any one of these surfaces may have a DFT outside the specified range, and hence, shall be measured. If the thick-ness of the flange is less than 1 inch (25 mm), the contracting parties may choose not to measure the DFT on the toe, i.e., surfaces 2, 6, 8, and 12 of Figure A2. As an informal initial survey, the inspector may want to check for uniformity of DFT across each surface. Is the DFT of the flange near the fillet the same as near the toe? Is the DFT uniform across the web? The inspector must be sure to use a gage that is not susceptible to edge effects. Follow the gage manufacturer’s instructions when measuring the edges.
A2.2 Full DFT Determination of a Beam: Divide the beam or girder into five equal sections along its length. Identify the 12 surfaces of the beam as shown in Figure A2 for each section. For tall beams where the height of the beam is 36 inches (91 cm) or more, divide the web in half along the length of the beam. For the full DFT determination, each half of the web is considered a separate surface. Take one spot measure-ment (as defined in Section 8.1) on surface 1 in each of the five sections. The location of the surface 1 measurement within a section is arbitrarily chosen by the inspector in each of the five sections. The average of these five spot measurements is the
FIGURE A2 THE SURFACES OF A STEEL BEAM
(36 in [91 cm] in height)
1
8 9
7
Less than 36 inches (91 cm) in height 12 Spots
5
2
10
6
4
3 11
Top Flange
12
Fillet
Bottom Flange
Web
Toe
36 inches (91 cm) in height or greater 14 Spots
1
5
2
10b bbb
10t
8 6
4b
9
4t
7
3 11 12
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DFT of surface 1. Repeat for the other 11 surfaces (7 surfaces if the toe is not measured; 14 surfaces for tall beams). The data can be reported in a format shown in Table A2.
A2.3 If Coating Thickness Restriction Level 3 is invoked by the specification (or if no Restriction Level is invoked by the specification), then no single spot measurement can be less than 80% of the specified minimum DFT, and no single spot measurement can be more than 120% of the specified maximum DFT. The average value for each surface must conform to the specified DFT. (There will be only eight average values if the DFT of the toe is not measured; there may be as many as 14 average values for beams greater than 36 inches in height.)
A2.4 SAMPLE DFT DETERMINATION OF A BEAM: In lieu of a full DFT determination of each beam, the job speci-fication may require only a sample DFT determination for selected beams less than 60 ft (18 m) long. For a sample DFT
determination, the web of beams less than 36 inches (91 cm) in height is not split.
A2.4.1 Beams less than 6 m (20 ft) in length: For beams less than 20 ft (6 m) in length, take two spot measurements, randomly distributed, on each of the 12 surfaces (8 surfaces if the toe is not measured) of the beam as defined in Figure A2. Each spot measurement must conform to the specified DFT.
A2.4.2 Beams 20 ft (6 m) up to 60 ft (18 m) in length: For beams 20 ft (6 m) up to 60 ft (18 m) in length, take three spot measurements, randomly distributed, on each of the 12 surfaces (8 surfaces if the toe is not measured) of the beam as defined in Figure A2. Each spot measurement must conform to the specified DFT.
A2.5 NON-CONFORMANCE: If any spot measurement falls outside the specified range, additional measurements may be made to define the non-conforming area.
TABLE A2.1 – NUMBER OF SPOT MEASUREMENTS NEEDEDON EACH SURFACE OF A BEAM FOR A FULL OR A SAMPLE DFT DETERMINATION
Number of Spot Measurements per SurfaceLength of Beam Full DFT Determination* Sample DFT Determinationless than 20 ft (6 m) 5 2from 20 to 60 ft (6 to 18 m) 5 3over 60 ft (18 m) 5 NA
* For beams 36 inches (91 cm) or more, the top half and the bottom half of the web are treated as separate surfaces in a full DFT determination.
TABLE A2 DATASHEET FOR RECORDING SPOT MEASUREMENTS AND
AVERAGE DFT VALUES FOR THE 12 SURFACES OF A BEAM OR GIRDER
Spot Measurements of DFT on Beam # _______________Surface Section 1 Section 2 Section 3 Section 4 Section 5 Average
1234t4b56789
10t10b1112
t = top half of web (for beams equal to or greater than 36 in [91 cm] in height)b = bottom half of web (for beams equal to or greater than 36 in [91 cm] in height)
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A2.6 RESTRICTED ACCESS: If the beam is situated such that one or more of the surfaces are not accessible, take measurements on each accessible surface in accordance with Section A2.2 or Section A2.4 through A2.4.2, as specified.
A2.7 ATTACHMENTS: Stiffeners and other attachments
to a beam shall be arbitrarily measured.
APPENDIX 3 - Methods for Measuring Dry Film Thickness for a Laydown of Beams, Structural Steel, and Miscellaneous Parts After Shop Coating
Appendix 3 is not a mandatory part of this standard, but it provides two sample protocols for measuring DFT for a laydown.
A3.1 GENERAL: A “laydown” is a group of steel members laid down to be painted in one shift by one painter. For inspec-tion of a laydown, first make a visual survey to detect areas with obvious defects, such as poor coverage, and correct as necessary. As an informal initial survey, the inspector may want to check for uniformity of DFT across each surface.
A3.2 FULL DFT DETERMINATION
A3.2.1 Beam (Girder): Follow the procedure described in Section A2.2.
A3.2.2 Miscellaneous Parts: Take 1 spot measurement (as defined in Section 8.1) on each surface of the part. If the part has fewer than 5 surfaces, take multiple spot measure-ments on the larger surfaces to bring the total to 5. If the total area of the part is over 100 ft2 (10 m2), take 5 spot measure-ments randomly distributed over the part for each 100 ft2 (10 m2), or fraction thereof.
A3.3 If Coating Thickness Restriction Level 3 is invoked by the specification (or if no Restriction Level is invoked by the specification), then no single spot measurement can be less than 80% of the specified minimum DFT, and no single spot measurement can be more than 120% of the specified maximum DFT. The average value of the spot measurements on each surface must conform to the specified DFT. If there is only a single spot measurement on a surface, it must conform to the specified DFT.
A3.4 SAMPLE DFT DETERMINATION: In lieu of a full DFT determination of each painted piece as described in Section A2.2, the job specification may require only a sample DFT determination for selected pieces.
A3.4.1 Beams less than 20 ft (6 m): Follow the procedure described in Section A2.4.1.
A3.4.2 Beams greater than 20 ft (6 m): up to 60 ft (18 m) in length: Follow the procedure described in Section A2.4.2.
A3.4.3 Miscellaneous parts: For a miscellaneous part, take three spot measurements, randomly distributed on the
part. Each spot measurement must conform to the specified DFT.
A3.5 NON-CONFORMANCE: If any spot measurement falls outside the specified range, additional measurements may be made to define the non-conforming area.
A3.6 RESTRICTED ACCESS: If a beam or miscellaneous part is situated such that one or more of the surfaces are not accessible, take measurements on each accessible surface in accordance with Section A2.2 or Section A2.4, as specified.
A3.7 NUMBER OF BEAMS OR PARTS TO MEASURE: In a laydown, the number of beams or parts to receive a full DFT determination and the number to have a sample DFT determination can be specified. For example, do a full DFT determination on a piece painted near the beginning of the shift, near the middle of the shift, and near the end of the shift in accordance with Section A3.2; and perform a sample DFT determination on every third piece in accordance with Section A3.4.
A3.8 ATTACHMENTS: Stiffeners and other attachments to a beam shall be arbitrarily measured.
APPENDIX 4 - Method for Measuring Dry Film Thick-ness on Coated Steel Test Panels
Appendix 4 is not a mandatory part of this standard, but it provides a sample protocol for measuring DFT on coated steel test panels.
A4.1 PANEL SIZE: The test panel shall have a minimum area of 18 in2 (116 cm2) and a maximum area of 144 in2 (930 cm2); e.g., minimum 3 x 6 inch (7.5 x 15 cm) and maximum 12 x 12 inch (30 x 30 cm).
A4.2 PROCEDURE: Use a Type 2 electronic gage. Take two spot readings from the top third, the middle third, and the bottom third of the test panel. Readings shall be taken at least ½ inch (12 mm) from any edge and 1 inch (25 mm) from any other spot reading. Discard any unusually high or low gage reading that cannot be repeated consistently. The DFT of the test panel is the average of the six acceptable spot readings.
A4.3 MINIMUM THICKNESS: The average of the accept-able spot readings shall be no less than the specified minimum thickness. No single spot reading shall be less than 80% of the specified minimum.
A4.4 MAXIMUM THICKNESS: The average of the acceptable spot readings shall be no more than the specified maximum thickness. No single spot reading shall be more than 120% of the specified maximum.
A4.5 REJECTION: If a spot reading is less than 80% of the specified minimum DFT or exceeds 120% of the speci-fied maximum DFT, additional measurements may be made to reevaluate the DFT on the area of the test panel near the
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low or high spot reading. If the additional measurements indi-cate the DFT in the disputed area of the panel to be below the minimum or above the maximum allowable DFT, the panel shall be rejected.
APPENDIX 5 - Method for Measuring Dry Film Thick-ness of Thin Coatings on Coated Steel Test Panels that have been Abrasive Blast Cleaned
Appendix 5 is not a mandatory part of this standard, but it provides a sample protocol for measuring DFT of thin coat-ings on coated steel test panels that had been abrasive blast cleaned.
A5.1 For the purposes of this standard, a coating is defined as thin if the dry film thickness (DFT) is on the order of 1 mil (25 µm) or less. Because the DFT is the same order as the statistical fluctuations of a DFT gage on bare blast cleaned steel, many gage readings must be taken to get a meaningful average.
A5.2 PANEL SIZE: The test panel shall have a minimum area of 18 in2 (116 cm2) and a maximum area of 144 in2 (930 cm2); e.g., minimum 3 x 6 inch (7.5 x 15 cm) and maximum 12 x 12 inch (30 x 30 cm).
A5.3 PROCEDURE: Use a properly adjusted Type 2 electronic gage. Take ten gage readings randomly distributed in the top third of the panel. Compute the mean (average) and standard deviation of these ten readings. Similarly, take ten readings from the middle third and ten readings from the bottom third of the test panel and compute their means and standard deviations. Readings shall be taken at least ½ inch (12 mm) from any edge and 1 inch (25 mm) from any other gage reading. Discard any unusually high or low gage reading, i.e., a reading that is more than three standard deviations from the mean. The DFT of the test panel is the average of the three means.
A5.4 MINIMUM THICKNESS: The average of the means shall be no less than the specified minimum thickness. No single mean shall be less than 80% of the specified minimum.
A5.5 MAXIMUM THICKNESS: The average of the means shall be no more than the specified maximum thickness. No single mean shall be more than 120% of the specified maximum.
APPENDIX 6 - Method for Measuring fhe Dry Film Thickness of Coatings on Edges
Appendix 6 is not a mandatory part of this standard, but it provides a sample protocol for measuring DFT of coatings on edges.
A6.1 Type 2 gage manufacturers offer a variety of probe configurations, some of which are less affected by proximity to edges and are designed to better measure the thickness of coatings on edges. The user should consult the gage manu-facturer’s instructions before measuring coating thickness on edges. SSPC-PA Guide 11 describes the use of coatings with edge retention properties and references a method (MIL-PRF-23236D) for assessing edge retention properties of coatings.
A6.2 Prior to measurement of coating on edges, the gage and probe should be verified for accuracy by placing a thin, flexible shim onto the prepared, uncoated edge. Adjustments to the gage may or may not be required. This procedure also verifies that the probe configuration will accommodate the edge configuration prior to coating thickness data acquisition.
A6.3 Obtain a minimum of three gage readings within 1.5 linear inches (~4 linear cm) of coated edge. The average of the gage readings is considered a spot reading. The number of spot readings along the edge will vary depending on the total length of the coated edge.
APPENDIX 7 – Method for Measuring Dry Film Thickness on Coated Steel Pipe Exterior
Appendix 7 is not a mandatory part of this standard, but it provides a sample protocol for measuring DFT of the exterior of coated pipe.
A7.1 Pipe sections that are loaded onto a cart or rack are considered a complete unit, as opposed to a single joint of pipe. The total number of spot and area measurements is based on the total square footage of pipe on the cart or rack. The square footage can be calculated using the formula below:
Area = (length of each pipe x circumference) x number of pipe sections on cart or rack
A7.2 Some carts may have several small items that could exceed the number of spot DFT readings required based on
TABLE A7NUMBER AND LOCATIONS OF SPOT MEASUREMENTS – PIPE SPOOLS
Pipe Diameter Circumferential Spot Measurements Interval Spacing
Up to 12 in (30 cm) 4 evenly spaced 10 feet (3 meters) apart
14 to 24 inches (36-60 cm) 6 evenly spaced 10 feet (3 meters) apart
Greater than 24 inches (60 cm) 8 evenly spaced 10 feet (3 meters) apart
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total square footage. In this case, the Owner/Contractor may select a Pipe DFT frequency Level shown below:
A7.2.1 Pipe DFT Level 1 Area = (length of each pipe x circumference) x no. of pipe sections on cart or rack = (number of spot measurements) x 2
A7.2.2 Pipe DFT Level 2 Area = (length of each pipe x circumference) x no. of pipe sections on cart or rack = (number of spot measurements) x 3
A7.2.3 Pipe DFT Level 3 Area = (length of each pipe x circumference) x no. of pipe sections on cart or rack = (number of spot measurements) x 4
A7.2.4 Pipe DFT Level 4 Area = (length of each pipe x circumference) x no. of pipe sections on cart or rack = (number of spot measurements) x 5
A7.2.5 Pipe DFT Level 5 Area = (length of each pipe x circumference) x no. of pipe sections on cart or rack = (number of spot measurements) x 6
A7.3 Pipe spools that are not loaded onto a rack or cart are measured individually. The number and locations of spot measurements are based on Table A7. Three sets of four circumferential spot measurements should be obtained on pipe spools less than 10 feet (3 meters) in length.
A7.4 A challenge for the painter in coating fabricated pipe spools is providing a uniform thickness throughout the entire surface. On a fabricated pipe spool, valves, flanges, and elbows tend to have low or high DFTs when compared to the straight run section. Painters may develop a pattern of work for a specific task. Hence, the DFT on the flange and valves may be consistently on the high side or the low side of the target DFT. This type of error is easy to detect and correct. Random errors pose a more difficult problem. Gross errors where the paint is obviously too thin or too thick must be corrected and are beyond the scope of this standard.
The number of spot measurements in this protocol may far exceed the “5 spot measurement per 100 ft2 (10 m2)” required in the standard. The full DFT determination, described in Table
A7, provides a very thorough inspection of a joint of pipe. The DFT determination, described in Section A7.1, may allow for fewer spot measurements. The user does not have to require a full DFT determination for every joint of pipe. For example, the requirement may be for a full DFT determination on one pipe out of ten, or a sample DFT determination on one pipe out of five, or a combination of full and sample DFT determinations.
APPENDIX 8 - Examples of the Adjustment of Type 2 Gages Using Shims
Appendix 8 does not form a mandatory part of this stan-dard, but it provides examples of how to adjust Type 2 gages using shims on roughened (e.g., abrasive blast cleaned) surfaces.
This example describes a method of adjustment to improve the effectiveness of a Type 2 (electronic) gage on a blast cleaned or otherwise roughened surface. Blast cleaning is used throughout this example, but these methods are appli-cable to other types of surface preparation. A less uniform surface, such as partially rusted hand tool cleaned steel, may require more gage readings to achieve a satisfactory level of statistical significance. Since gage operation differs among manufacturers, follow the manufacturer’s instructions for adjustment of a particular gage.
A Type 2 gage needs to be adjusted to account for the profile of the substrate in order to read the coating thickness directly. Type 2 gages equipped with double pole probes may provide greater measuring precision on rough surfaces compared to single pole probes.
A portion of the substrate, after blast cleaning but prior to coating, can be used to adjust the gage. Alternatively, an uncoated test panel, blast cleaned at the time the structure was blast cleaned and having a profile representative of the structure can be used to adjust the gage provided the test panel is of material with similar magnetic properties and geom-etry as the substrate to be measured. If this is not available then a correction value can be applied to a smooth surface adjustment as described in A8.3.
Three adjustment techniques can be used depending on the capability and features of the gage to be used for the inspection. Note that due to the statistical variation produced
TABLE A8 TYPICAL GAGE CORRECTION VALUES USING ISO 8503 PROFILE GRADES
(SOURCE: ISO 19840)1
ISO 8503 Profile Grade Correction Value (mil) Correction Value (µm)
Fine 0.4 10
Medium 1.0 25
Coarse 1.6 40
1 International Organization for Standardization (ISO), Case Postale 56, Geneva CH-1211, Switzerland. ISO standards are available online from the American National Standards Institute (ANSI), 1819 L Street, NW, Suite 600, Washington, DC 20036 or at <http://www.ansi.org>
SSPC-PA 2May 1, 2012
11
by a roughened surface, individual readings taken using these three methods may not perfectly agree.
The first two examples describe adjustment and verifica-tion to one or more shims. When shims are used, resultant gage measurements are less accurate and must be recalcu-lated. For example, if the accuracy of a properly calibrated gage is ± 2% and the thickness of a shim is accurate to within ± 3%, the combined tolerance of the gage and the shim will be ± 4% as given by the sum of squares formula:
√22 + 32 = 3.6055 ≈ 4%
For the gage to be in agreement with the shim, the average thickness measured by the gage must be within ±4% of the shim’s thickness. If the average thickness measured on a 250-µm (10-mil) shim is between 9.6 mils (240 µm) and 10.4 mils (260 µm), the gage is properly adjusted. The minimum 240 is 250 minus 4% of 250 (9.6 is 10 minus 4% of 10); the maximum of 260 is 250 plus 4% of 250 (10.4 is 10 plus 4% of 10). [4% of 250 is 10; 4% of 10 is 0.4.]
A8.1 SINGLE POINT ADJUSTMENT: This example uses a single shim value at or close to the thickness to be measured. The thickness range over which this adjustment achieves the required accuracy will vary with gage design.
Assuming that the coating thickness to be measured is 4.0 mil (100 µm) then a shim of approximately 4.0 mil (100 µm) or slightly greater should be used to adjust the gage. The shim is placed on an area of the substrate that has been blast cleaned to the required standards, or on a blasted test coupon with a similar surface profile.
The average of 10 readings on the shim is sufficient to allow for the statistical variation in the blast profile.
A8.2 TWO POINT ADJUSTMENT: This example uses two shim values, one above and one below the expected film thickness to be measured. It should be noted that not all film thickness gages can be adjusted in this manner.
Assuming that the coating thickness to be measured is 4.0 mil (100 µm) then shims of 10.0 mil (250 µm) and 2.0 mil (50 µm) are appropriate for setting the upper and lower values on the scale of the gage.
As protective coatings are normally applied to blast cleaned metal surfaces, a statistical approach is required to obtain a typical value for the adjustment. Ten readings on a shim are sufficient to establish a reliable average value for that shim on the roughened surface. Following the manufacturer’s instructions, the gage is adjusted so that the actual shim thick-ness is then used to set the gage.
This procedure should be repeated for both the upper and lower shim values.
The average of 10 readings on an intermediate shim, approximately 4.0 mil (100 µm) thick in the case described above, will confirm that the gage has been adjusted correctly. It is acceptable for the average reading to be within ± 4% of the shim thickness.
This method ensures that the gage reads the thickness of the coating over the peaks of the profile.
A8.3 SMOOTH SURFACE ADJUSTMENT: If access to the bare blast cleaned substrate is not available because the coating already covers it, a smooth surface can be used to adjust the gage. Adjust the gage on a smooth surface according to the manufacturer’s instructions. Alternatively, it may be possible to adjust some Type 2 gages through the coating already applied to an abrasive blast cleaned substrate (may be necessary if no uncoated substrate exists). This procedure should be performed according to the manufac-turer’s instructions.
Readings taken on the blast-cleaned substrate will be higher than the true value by an amount dependant on the surface profile and the gage probe design. For most appli-cations a correction value of 1.0 mil (25 µm) is generally applicable. Note that this value is not related to the actual surface profile measurement. This correction value must be subtracted from each gage reading to correct for the effect of the profile. The resulting corrected reading represents the thickness of the coating over the peaks.
For fine profiles the correction value may be as low as 0.4 mil (10 µm) but for coarse profiles it could be as high as 1.6 mil (40 µm). Table A8 gives approximate correction values to be used when a blast-cleaned surface is not available to adjust the gage.
The use of coated standards to adjust gages means that a correction value must be applied to readings, as the coated standards make use of smooth substrate surfaces.
Copyright ©SSPC standards, guides, and technical reports are copyrighted world-wide by SSPC: The Society for Protective Coatings. Any photocopying, re-selling, or redistribution of these standards, guides, and technical reports by printed, electronic, or any other means is strictly prohibited without the express written consent of SSPC: The Society of Protective Coatings and a formal licensing agreement.
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