TNT The NDT Technician A Quarterly Publication for the NDT Practitioner W hy is it necessary to obtain thickness measurements on equipment operating at temperatures from 300 ºF to 1200 ºF (150 ºC to 650 ºC)? Simply put, decisions about corrosion and erosion of piping and pressure vessels must be made based on immediate measurements that accurately reflect the high temperature environment. What industries require this type of corrosion information at high temperature? Oil refineries and chemical plants are the principal industries requiring measurements in such corrosive and heated environments and these industries have adopted onstream inspection point systems to achieve them. Measurements made in onstream inspection point systems are recorded at the same point each time at predetermined intervals in order to accurately assess the rates of corrosion and erosion and to project needed replacements. How can ultrasonic measurements be obtained at elevated temperatures? The answer, needless to say, is very carefully. Protective equipment is required for the technician to prevent burns and for the ultrasonic testing equipment to prevent damage to the transducer and cables. History The earliest thickness measurements in the petrochemical industry (1958-62) were obtained using resonance measurement techniques in which resonance principles were used to determine velocity or thickness. The equipment was of two types; the first based upon interpreting audible beeps and the second based on interpreting visible indications on a cathode ray tube. The instruments were accurate but required surface preparation and the transducers used could not withstand temperatures in excess of 150 ºF (65 ºC). Early pulse echo instruments were often used in tandem with resonance equipment and eventually replaced the resonance measurement technique. Pulse echo instruments could be used with flowing water that acted as couplant and also kept the transducer cool. However, metallurgists were concerned that these instruments might quench the material or cause thin wall piping to rupture. Ensuing technology substituted a liquid filled chamber in place of flowing water. Diagrams for a flowing water system and an early high temperature prototype transducer with liquid filled chamber are shown in Figs. 1 and 2. As technology continued to evolve, the liquid filled chamber was replaced with a solid cylinder of interchangeable lengths. This transducer type is typically used as a single element transducer and is most effective with analog ultrasonic instruments. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Volume 3, Number 4 October 2004 Focus: Ultrasonic Thickness Measurements at High Temperatures. 1 Tech Toon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 FYI: Practical Contact Ultrasonics — Angle Beam Calibration Using a Basic Calibration Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Feature: Job Safety: Slips, Trips and Falls . . . . . . . . . . . . . . . . . . . . . . 8 Practitioner Profile: Anthony J. Gatti, Sr. . . . . . . . . . . . . . . . . . . . 10 Inbox: Number Belts for Pipe Welds . . . . . . . . . . . . . . . . . . . . . . . . 11 A Publication of the American Society for Nondestructive Testing Focus Ultrasonic Thickness Measurements at High Temperatures by Ronald T. Nisbet CONTENTS TNT The NDT Technician A Quarterly Publication for the NDT Practitioner Continued on page 2. Backing material Bubbler attachment Figure 1. Early pulse-echo instrument using flowing water as couplant and coolant. Transducer Flowing water supply Legend Water Liquid filled chamber Test piece Figure 2. Early high temperature transducer with liquid filled chamber. Transducer Legend Rubber diaphragm. Couplant
Transcript
TTNNTTThe NDT Technician A Quarter ly Publ icat ion for the NDT Pract it ioner
W hy is it necessary to obtain thicknessmeasurements on equipmentoperating at temperatures from
300 ºF to 1200 ºF (150 ºC to 650 ºC)? Simply put,decisions about corrosion and erosion of pipingand pressure vessels must be made based onimmediate measurements that accuratelyreflect the high temperature environment.
What industries require this type ofcorrosion information at high temperature? Oilrefineries and chemical plants are the principalindustries requiring measurements in suchcorrosive and heated environments and theseindustries have adopted onstream inspectionpoint systems to achieve them. Measurementsmade in onstream inspection point systems arerecorded at the same point each time atpredetermined intervals in order to accuratelyassess the rates of corrosion and erosion and toproject needed replacements.
How can ultrasonic measurements beobtained at elevated temperatures? Theanswer, needless to say, is very carefully.Protective equipment is required for thetechnician to prevent burns and for theultrasonic testing equipment to preventdamage to the transducer and cables.
History
The earliest thickness measurements in thepetrochemical industry (1958-62) were obtainedusing resonance measurement techniques inwhich resonance principles were used todetermine velocity or thickness. The equipmentwas of two types; the first based uponinterpreting audible beeps and the secondbased on interpreting visible indications on acathode ray tube. The instruments wereaccurate but required surface preparation andthe transducers used could not withstandtemperatures in excess of 150 ºF (65 ºC).
Early pulse echo instruments were oftenused in tandem with resonance equipment andeventually replaced the resonancemeasurement technique. Pulse echoinstruments could be used with flowing waterthat acted as couplant and also kept thetransducer cool. However, metallurgists wereconcerned that these instruments might quenchthe material or cause thin wall piping torupture. Ensuing technology substituted a liquidfilled chamber in place of flowing water.Diagrams for a flowing water system and anearly high temperature prototype transducerwith liquid filled chamber are shown in Figs. 1and 2. As technology continued to evolve, theliquid filled chamber was replaced with a solidcylinder of interchangeable lengths. Thistransducer type is typically used as a singleelement transducer and is most effective withanalog ultrasonic instruments. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Volume 3, Number 4 October 2004
Focus: Ultrasonic Thickness Measurements at High Temperatures. 1
A Publication of the American Society for Nondestructive Testing
FocusUltrasonic ThicknessMeasurements atHigh Temperaturesby Ronald T. Nisbet
CONTENTS
TTNNTTThe NDT Technician A Quarter ly Publ icat ion for the NDT Pract it ioner
Continued on page 2.
Backing material
Bubblerattachment
Figure 1. Early pulse-echo instrument usingflowing water as couplant and coolant.
Transducer
Flowingwatersupply
LegendWater
Liquid filled chamber
Test piece
Figure 2. Early high temperature transducerwith liquid filled chamber.
Transducer
LegendRubber diaphragm.Couplant
2 · 10/2004 · The NDT Technician
Tech Toon
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FROM THE EDITOR
W hen asked what advice he would offer tosomeone considering NDT as a career, TonyGatti answered, “If you’re gonna do it, do
whatever it takes.” In other words, to do it well, youhave to commit. Certainly, Anthony’s commitment isapparent. He’s been on the decks of the many shipsand submarines that he’s inspected bearings for andhe’s been to the very bottom of Hoover Dam andstood in front of the huge new turbines thatincorporate his inspection product. Interesting andimportant work — he’s justly proud. Not all of us workon projects as interesting as Hoover Dam but becausethe NDT community strives to ensure that the productis what it’s said to be, NDT is important work.
This month, Ron Nisbet’s Focus article discussesthickness measurements made in high temperatureenvironments and Jim Houf has prepared the fiftharticle in the popular FYI Practical Contact Ultrasonicsseries. The topic is ASME type angle beam calibration.There’s also a feature on falls in the workplace with aninteresting table that breaks out the principal types ofwork-related falls and the relative incidence of eachtype. The second leading cause of accidental death onthe job, how falls happen and what we can do toeliminate their potential is good information weshould always keep in mind.
Most ultrasonic thickness measurements madetoday use modern equipment that features bothan A–scan display and digital thicknessmeasurement (Fig. 3). Additionally, transducershave been developed for use at temperaturesranging from ambient up to 800 ºF (427 ºC). Asection view of a popular transducer that can beused up to about 700 ºF (370 ºC) is shown inFig. 4. When temperature exceeds 800 ºF (427 ºC),the single transducer with a heat resistantstand–off (coupling block used between the faceof the contact transducer and the front surface ofthe test object) can often be used with a flawdetector.
“Seems like we do this drop test earlier every year, Harve.”
Focus continued from page 1.
Figure 3. Modern UT equipment features bothA–scan display and digital thickness reading.
Backing material
Receiving crystalelement
Temperature resistantstand–off material
Wear plate
Figure 4. Diagram and section views of atransducer suitable for temperature up to700 ºF (370 ºC).
Transmittingcrystal
element
10/2004 · The NDT Technician · 3
Understanding the Effects of HighTemperature Environments
To conduct effective high temperaturemeasurements, it is important to understandhow increases in temperature affect materialproperties, the ultrasonic signal and couplant.Effects of Heat in Signal and MaterialProperties. Increase in temperature affectsboth velocity of the sound wave andattenuation. In high temperature environments,the velocity of sound decreases. Astemperatures increase within a material, themolecules of the material begin to bouncerapidly in a random motion and as a result, theultrasound signal or wave of vibration transmitsless and less effectively. In carbon steel thedecrease in velocity is about one percent forevery 100 ºF or 55 ºC. For the same reason,attenuation, or loss of energy, increases in hightemperature materials and it becomes moredifficult to obtain a strong recognizable signal.Properties of Couplant. Couplant propertiesfactor significantly among the difficultiesincurred in high temperature environments. It iscouplant that excludes the air gap betweentransducer face and workpiece and permitssound to be transmitted into the material undertest. At high temperatures, typical couplantevaporates. Special couplants have beenformulated for use at various ranges oftemperature. Liquid viscous couplants are mosteffective at ambient temperatures. At very hightemperatures, couplants that are paste at roomtemperatures become liquid when applied to ahot surface. In these extreme conditions, dwelltime for even the best couplant is short. Thesignal appears briefly, then diminishes rapidlybefore disappearing completely. Instrumentswith a freeze function are useful in retainingthis short-lived signal for evaluation.
Compensating for Error in HighTemperature Measurements
The two main sources of error that occur inhigh temperature measurements are due to:• reduction in velocity in the heated measured
material and• change in zero calibration that occurs when
the stand–off material becomes heated.When the velocity of sound is decreased, thepulse takes longer to return to the transducerand the measurement appears higher than theactual material thickness. The error is greater inthicker material and increases as temperatureincreases (about one percent additionalthickness for every 100 ºF or 55 ºC). As thestand–off material between transducer andworkpiece heats up, the velocity of sound in thestand–off itself decreases. This changes the zerooffset of the transducer and results in anincrease in the apparent thickness reading asthe transducer heats up. The amount of changedepends on the transducer and stand–offmaterial and is the same for the material beingexamined regardless of thickness. As a result,transducers must be cooled between readings.The problematic changes in sound velocity thatoccur in heated materials can be addressed ineither of two ways. The calibration block can beplaced on the heated test piece and allowed toreach the temperature of the test piece beforecalibration is made on the heated block ormeasurements can be corrected after they havebeen taken to compensate for the effect oftemperature on sound velocity.Heating the Calibration Block. From a practicalstandpoint, heating the calibration block hasseveral disadvantages:• Additional time is needed to heat the
calibration block to the temperature of thetest piece.
• It is difficult to determine when thecalibration block has reached thetemperature of the test piece.
• It is often difficult to find an exposed portionof the test piece operating at the desiredtemperature.
Corrected Measurements. As an alternative toheating the calibration block, method twocompensates for changes in velocity bycorrecting measurements after they are taken.This is done by using a device to measuretemperature and a correction table (Table 1) orby applying a formula that makes a correctionof one percent per 100 ºF or 55 ºC oftemperature change.
Ta = Tm x [1.007 – (0.0001 × t)]Where:Ta = corrected thickness of the partTm = measured thickness of the partt = surface temperature of the part in ºF
Correcting measurements after they are takenusing a correction table or formula is more costeffective than heating the calibration block andequally as accurate. Correction or compensationmethods have been incorporated into thetechnology of many new ultrasonic instruments.Accessing Inspection Points. Another practicalcomplication to high temperature ultrasonicthickness measurement is that most piping andvessels operating at high temperatures areinsulated. Access for ultrasonic measurement isthrough holes cut in the insulation. Whenthickness of the insulation and/or diameter ofthe access holes do not permit holding thetransducer in the hand, an extension devicemust be used to make proper contact with themeasurement surface. In this instance, extracare is needed to ensure that the transducerface is flat on the inspection surface.
Conclusion
The factors found in high temperatureenvironments such as extreme heat, couplantvaporization, signal attenuation, difficulty inmanipulating the transducer and the additionaltime required for cooling the transducercontribute to a difficult working environment.To obtain accurate thickness measurements onhigh temperature materials, the operator musthave a clear understanding of the process,follow proper safety precautions, makeappropriate use of the correction factor andabove all, exercise patience and perseverance.TNT
Ronald T. Nisbet is a professional engineer inthe state of California and an ASNT NDT Level III with more than forty years experiencein the NDT of materials in the petrochemicalindustry. He is currently vice-chair of the ASNTStandards Development Committee.(310) 257-8222, (310) 257-8220 fax,<[email protected]>.
1000 (538)
900 (482)
800 (427)
700 (371)
600 (316)
500 (260)
400 (204)
300 (149)
200 (93)
100 (38)
Tem
per
atu
re, º
F (º
C)
0
0.1
(0.3
)
0.2
(0.5
)
0.3
(0.8
)
0.4
(1.0
)
0.5
(1.3
)
0.6
(1.5
)
0.7
(1.8
)
0.8
(2.0
)
0.9
(2.3
)
1.0
(2.5
)
1.1
(2.8
)
1.2
(3.0
)
1.3
(3.3
)
1.4
(3.6
)
1.5
(3.8
)
1.6
(4.1
)
1.7
(4.3
)
1.8
(4.6
)
1.9
(4.8
)
2.0
(5.1
)
Table 1. Ultrasonic thickness correction for high temperature. Follow slanting line from basefor given thickness reading to the horizontal temperature. Drop vertically to base line toobtain corrected thickness.
Thickness, in. (cm)
A rticle four of this series, IIW BasedAngle Beam Calibration, discussedangle beam calibration using the
IIW block and some of its derivatives. With theIIW block, the reference reflector is a singlereflector that results in a single screen trace, or ifthe sound path is long enough, in a second tracefarther down the time line. Most codes andspecifications that specify IIW calibration rely ona simple formula to account for attenuation orloss of sound that occurs as the sound beamtravels through the part being inspected.
An alternative method of angle beam UTcalibration for welds uses a calibration blockwith three side-drilled holes called a basiccalibration block. All three holes are of the samediameter and are used to determine the amountof sound energy returned from a reflector of thesame size at different sound paths. Basiccalibration blocks are referenced in Article 5 ofSection V: Ultrasonic Examination Methods forMaterials and Fabrication of the ASME Boilerand Pressure Vessel Code and thus are oftenreferred to as ASME Cal Blocks. The blockdiscussed in this article is shown in Fig. 542.2.1 inArticle 5 (1999 Addenda) of this code. Asimplified version is recreated here in Fig. 1.
The Basic Calibration Block
The thickness of the weld being inspecteddetermines the size of the calibration block tobe used. One of the benefits of using the basiccalibration block is that Section V of the ASMEBoiler and Pressure Vessel Code permits using ablock of a particular thickness to cover a rangeof weld thicknesses. For example, a 3/4 in. thickblock can be used for welds with a thickness of1 in. or less; a 1 1/2 in. thick block can be usedfor welds in the 1 to 2 in. range; a 3 in. thickblock can be used for welds in the 2 to 4 in.range, and so on. In all cases, a block the samethickness as the weld being inspected can beused. The major advantage of blocks that covera range of weld thicknesses is that an inspectionagency can manufacture two or three blocksthat will generally cover the full range of weldthicknesses that will normally be inspected.
As shown in Fig. 1, most blocks have astandard 6 in. width and a minimum length of
3t, where t is the block thickness. Whendetermining block length, the fabricator shouldconsider which transducer wedge angles will beused for the applicable range of weldthicknesses. Since a 70 degree wedge angleutilizes the longest sound path, a commonchoice is a block length slightly longer than thedistance required to accommodate a full skipdistance for a 70 degree probe. A block thislength can be used for 45 and 60 degreetransducers as well. Weight can become aconsideration on thicker blocks. For example, a5 in. thick carbon steel cal block that is 6 in. wideand 15 in. (3t) long will weigh about150 pounds, making it awkward to handle anddangerous if dropped. It is not uncommon tosee a handle welded on one end of blocks ofthis size to facilitate lifting with a crane.
The three side-drilled holes are located atthree distances (1/4t, 1/2t and 3/4t) from thescanning surface. Diameters for these side-drilled holes are described in a table (refer toFig. 542.2.1 of Section V) for each calibration
block thickness. As the blocks increase inthickness, hole diameter also increases creating alarger reflector that results in lower sensitivity.Thus, in thicker blocks, a discontinuity in a thinweld that might be rejectable may not berejectable in a thicker weld.
Nominal hole sizes for the various blockthicknesses are: a 3/32 in. diameter hole for a3/4 in. block, a 1/8 in. diameter hole for a1 1/2 in. block and a 3/16 in. diameter hole for a3 in. block. As block thickness increases in 2 in.increments, hole diameter increases by 1/16 in.Hole diameter tolerance is ± 1/32 in. for allblocks. Minimum hole depth is 1 1/2 in.
Another benefit of basic calibration blocks isthat their fabrication is relatively simple and canbe done in-house using a band saw, a drill pressand several different sized drill bits and reams. Apiece of acoustically similar steel of the correctthickness that has been properly heat-treated(refer to Article 5 of the ASME Boiler andPressure Vessel Code) should be scanned using astraight beam transducer to determine that thepiece is free of internal defects and laminations.It can then be cut to size using either a verticalor horizontal band saw.
Once the block is sized and soundness isconfirmed, holes can be drilled using a bit withthe proper diameter in a drill press. The holesmust then be reamed to ensure a smoothreflecting surface for the sound beam. Careshould be taken when choosing the size of thedrill bit. Most reamers remove 0.002-0.003 in. ofmaterial from each side of the hole thusrequiring that a slightly smaller bit be used.
At this point of fabrication, optional notchesin the top and bottom surfaces of the block can
be machined into the block if needed (refer toFig. T-542.2.1, Section V, Article 5 of the ASMEBoiler and Pressure Vessel Code for notchdimensions and positioning). The block is nowready for production calibrations.
The DAC Curve
A distance amplitude correction (DAC) curve isused to determine attenuation or degree ofsound loss that occurs as the ultrasonic soundpath increases in length. A reflector of knownsize close to the transducer (short sound path)returns more sound to the transducer than areflector of the same size that is farther away(long sound path). This is due in part to the factthat a sound beam spreads as it travels awayfrom the transducer, much like the cone of lightfrom a flashlight. Some attenuation or loss ofsound power also occurs as the sound beamtravels through the material of the test object.Any change in the wedge, transducer or coaxialcable can affect the amount of sound generatedand would therefore require a new DAC curveto be generated.
Loss of sound power as sound path lengthincreases is not linear. Use of a simple formulasuch as that used with the IIW block will notaccurately show the amount of sound returningto the transducer. The concept of using three
side-drilled holes of the same diameter atdifferent sound paths was developed tocompensate for any distance error in amplitudethat appears on the monitor.
Calibration Based On Hole Depth
Two techniques are commonly used incalibrating the basic calibration block. The firstuses the actual sound path to each hole toestablish screen width. The second uses the holedepth or distance from each hole to thescanning surface. The hole depth technique isthe more simple of the two calibration methods.Figure 2 shows correct positioning of thetransducer to locate the three holes using thefirst leg of the sound beam. Couplant is firstapplied to the surface of the block and thescreen trace representing the nearest hole (atthe 1/4t depth) is maximized. The left side of thetrace is positioned above the first majorgraticule on the screen baseline. Amplitude orscreen height of the trace is set at 80 percent offull screen height or FSH. The gain setting forthis amplitude is recorded as the reference level.The top of the trace is marked on the monitorwith a marker. (This can be marked electronicallyin newer equipment. See user’s manual).
Next, with no change to gain setting, movethe transducer backwards on the scanning
surface until the trace from the 1/4t hole (or7/4t) in the second leg is maximized. Position thescreen trace on the baseline at the seventhmajor graticule. Then, switching back and forthbetween the first and second leg signals, use therange and delay controls to set the two tracesover the proper graticules. (Controls for rangeand delay may vary on newer equipment.Consult user’s manual.) When this has beendone, the maximized screen traces from the 1/2t(2/4t) and 3/4t holes should show above thesecond and third graticules for the first leg andabove the sixth and fifth graticules for thesecond Leg. When locating the 3/4t hole, do notmistake the signal from the corner of the block,which may show up as a larger trace just to theright of the hole trace. The operator shouldthen go back to each hole location, maximizethe signal on the screen, mark the top of eachrespective trace with the grease pen and finallyconnect the dots in as smooth a line as possible.
This line becomes the DAC curve for that blockand equipment (Fig. 3). Note both ends of thecurve have been extended to include both thefirst and eighth graticules. In some cases, whenthe 1/4t hole trace is set at 80 percent FSH, itmay not be possible to see the traces at the sixthand/or seventh graticules. If this occurs, set thetrace from the 1/2t hole to 80 percent FSH asshown in Fig. 3 and use that gain setting as thereference level. Be sure to report that the 1/2thole was used to set the reference level.
The technique may seem confusing but Fig. 4can be of help. The full thickness of a block is 1t,which can also be written as 4/4t. The threeholes, if kept in 1/4t units, would be at 1/4t, 2/4tand 3/4t depths. Full thickness or 4/4t would bethe bottom surface of the block. In Fig. 4, aregular block is shown in solid lines with thestandard three holes. Directly below is a reverseor mirror image of the block that shows wherethose holes would be if the block were twice asthick. Total thickness is now twice that of thenormal block and is represented as 2t or, ifexpressed in 1/4t increments, 8/4t.
The second leg sound paths in Fig. 4 are alsoshown as if they continue straight on into themirror block instead of reflecting back from thebottom surface. In this way, the second legsignal for the 3/4t hole appears to be at the 5/4tdepth in the mirror block. Similarly, the 1/2t(2/4t) hole appears at 6/4t and the 1/4t holeappears at the 7/4t position. A full skip distance,two thicknesses, would be at the bottom of themirror block or at the top of the regular block.
Now consider the screen positions of the sixtraces that make up the DAC curve. In the firstleg, the 1/4t trace is at graticule 1, the 2/4t traceis at graticule 2, the 3/4t trace is at graticule 3and there is no trace at graticule 4 (the bottomof the block). In the second leg, the 5/4t trace isat graticule 5, the 6/4t trace is at graticule 6, the7/4t trace is at graticule 7 and there is no traceat graticule 8 (top of the actual block or bottomof the mirror block). These 1/4t designators areshown below the baseline in Fig. 3 and to theright of Fig. 4. There are several codes that referto the second leg points on a DAC curve as the5/4, 6/4 and 7/4 locations.
Calibration Using Sound Path
When calibrating using the sound path method,couplant is again applied to the surface of theblock and the signal returning from the nearesthole (at the 1/4t depth) is maximized. Then theoperator applies the trigonometric formula:
sin θ = opposite side ÷ hypotenuse
where θ is the the complementary angle of thewedge angle, opposite side is the distance fromthe scanning surface to the center of the hole,and the hypotenuse is the sound path. This is
shown graphically in Fig. 5. Remember that thewedge angle is the angle formed by a linenormal (90 degrees) to the scanning surface. Fora 70 degree wedge, θ is 20 degrees and for a60 degree wedge, θ is 30 degrees. With the45 degree wedge, both wedge andcomplementary angles are 45 degrees.
Once the sound path has been calculated,the left side of the screen trace for that hole isplaced on the screen at the distance thatrepresents that sound path. The amplitude(screen height) of the trace is set at 80 percentFSH. The gain setting for this amplitude isrecorded as the reference level. Then, with nochanges to the gain setting, the same operationis performed on the 1/2t hole, maximizing thereflector, calculating the sound path andlocating the trace at the proper location on the
monitor. In most cases, it will be necessary to goback and forth between the 1/4t and 1/2t holesto properly align both screen traces in theirproper screen locations using the range and
FYI continued from page 5.
Figure 3. Completed distance amplitude correction curve (DAC) in relation to fractions of blockthickness, t.
Screen width indicated with major graticules andfractions of block thickness, t
1/4t
2/4t
3/4tt
5/4t
6/4t
7/4t
2t
567
Figure 4. Second leg sound paths.
Hypotenuse
Opposite side
θ
90º - θ
Figure 5. Trigonometric sound pathcalculation.
FYI continued on page 9.
DAC curve
N DT technicians or inspectors are oftencalled upon to work above groundlevel on surfaces such as scaffolding,
ladders, narrow stairs, on elevated floors withunprotected edges or in areas where there maybe holes or openings in the walking surface.Slips, trips and falls from these areas are majorcauses of employee injury. The Bureau of LaborStatistics reports that, in 1994 alone, 376,900workers suffered injuries from falls thatrequired time off from work; and, from 1992thru 2002, there were some 7,626 fatalitiesattributed to falls. Falls are the second leadingcause of accidental death in the workplace.Because falls are such a frequent cause ofaccidents, it is important for you – the NDTtechnician – to be aware of the differentexposures that you may encounter and how toprotect yourself.
As children, we fell a lot. As adults, we findthat the sudden stop associated with falling ismuch more painful. Falls are usually the resultof poor work practices, poor site conditions or acombination of the two. As technicians orinspectors, we have to take measures to limitsituations or conditions that lead to falls andthe unnecessary injuries – or even death – thatcan result. Fall protection is an ongoing processand should be a part of every task or projectfrom the planning stage through completion.
Same Level Falls
A same level fall is a slip or trip that takesplace on the same level where you are workingor walking. Mishaps such as these are usually theresult of poor housekeeping or a lapse inattentiveness on the part of the person falling.Anyone who has worked on construction siteshas experienced the ever-present extensioncord, welding leads or electrodes, pieces ofconduit and other scrap in the traffic areas.Although good housekeeping is being stressedmore and more on construction sites, hazardswill always be present, especially when oneconsiders the potential danger introduced by oil,grease, mud, water or even snow and ice. Youprobably have little control over most of thehazards that cause same level fall hazards. Forthat reason, it is most important to be aware ofyour surroundings at all times.
Lower Level Falls
A lower level fall is a fall from one surface toa lower surface. Conditions in construction andindustry that can expose you to such fallsinclude pipe racks, rooftops, structural steel,deck openings, scaffolding, stairs, ladders andpersonnel baskets. Other hazards could be flooropenings for ladder-access or stairways.
Overall, fall protection requiresimplementation of the means necessary toprotect workers from fall hazards on the job. Asa first step, this would include identifyingpotential hazards and eliminating them.However, if the hazard can’t be eliminated, itbecomes necessary to prevent the fall fromoccurring or controlling the fall so that it doesn’tinjure the worker.
Fall Prevention
Fall prevention employs methods that restrain orprevent a worker from falling. This includesguardrails and the installation of barriers to helpcontrol lower level falls, well-marked hole oropening covers, perimeter guards (use of cablesor wire ropes, usually on structural steel). These
barriers are usually installed by the owner orgeneral contractor, but are not always availablein some situations. This initial system may haveto be supplied in some manner by the inspectoror technician.
Fall Protection
Fall protection provides a means to arrest thefall of one who has actually fallen. Fallprotection is required when working from anelevation of six feet or more above the groundor floor without the protection of approvedhandrails, cables or other fall preventionsystems. Even when standard guardrails arepresent or when working in aerial lifts orpersonnel baskets, it is still a recommendedpractice to use some form of fall protection.Personal Fall Arrest Systems. Fall protectiondevices or personal fall arrest systems aregenerally composed of several separatecomponents. The full-body safety harness isworn by the individual and is designed toeliminate headfirst falls and distribute fall-arresting forces across the major body parts inorder to minimize injury. The lanyard connectsto the harness from the immediate attachmentor intermediate anchorage point and must:• be capable of supporting 5,000 pounds,• limit free fall to six feet or less,• be attached as high as possible above the
point of operation to further limit free fall,• be used singly (never hook two lanyards
together),• be equipped with self-closing/locking snap
hooks,• be used with straight-loading hooks in order
to utilize the rated strength of the hook, and• not be wrapped around an anchorage point
(this reduces support capability).
8 · 10/2004 · The NDT Technician
How do we fall?
Example of accepted disabling workers’ compensation claims for the constructionindustry (state of Oregon 1997 - 2003).
Exposure event Number of claims PercentageFalls to a lower level 2,738 100
from ladders 923 33.7unspecified 482 17.6from roofs 371 13.6from scaffolds or staging 267 9.8from nonmoving vehicles 263 9.6floor, dock or ground level 226 8.3down stairs or steps 168 6.0from girders or structural steel 24 0.9from piled or stacked material 14 0.5
Falls on same level 1,296 100to floor, walk or other surface 770 59.4onto or against objects 357 27.5unspecified 169 13.0
Source: Oregon Department of Consumer and Business Services, Information ManagementDivision, Research and Analysis Section <www.cbs.state.or.us>
FeatureJob Safety: Slips, Tripsand Fallsby William W. Briody
10/2004 · The NDT Technician · 9
The intermediate attachment point is alifeline or retractable device generally designedto allow for freedom of movement. This isattached to the anchorage point(s), a securepoint of attachment that is independent of themeans of support or suspension for the worker.The system must support a minimum of5,000 pounds per worker attached. All fallprotection devices should be subject toinspection before and after use. Many types offall protection devices are available. Technologyfor the full-body harness has been greatlyimproved with various harness types nowavailable for different applications. There arealso a number of use specific lanyards available.
Conclusion
Many companies make fall protection part ofworkplace safety and health programs and theyfollow up with strict enforcement. Equipmentand training are significant parts of fallprotection, but equally important is thewillingness of the worker to employ those safework practices in place of risky ones. TNT
A Lifetime Member of ASNT, Bill Briody is currentlyChair of the Section Operations CouncilMembership Division and a member of theTechnicians Advisory Committee. (804) 264-2701,<[email protected]>
delay controls. The 3/4t hole trace and thesecond leg reflectors from all three holes arethen set up on the screen in a similar manner.This sets the screen width for the holes in theblock being used.
As with hole depth calibration, the operatormay find that the screen traces for the last twopositions, 1/2t and 1/4t holes in the second legof the sound path, may not be visible at therecorded reference level. This usually means thatthe 1/4t hole in the first leg was in the near fieldand cannot be used to develop the referencelevel. When this occurs, it is necessary to go backto the 1/2t hole (first leg), set that screen traceto 80 percent FSH and use that gain setting asthe reference level. If the 1/2t and 1/4t holes inthe second leg can be seen on the screen,calibration can be completed. Note that whenthe reference level is changed, sound pathlocations of all holes should be rechecked toensure the sound path is unchanged. If the lasttwo hole traces are still not visible, it may benecessary to change transducer sizes and/orfrequencies to reduce the near field to allowproper calibration.
Once traces from the six hole locations (threein the first leg and three in the second) are allproperly located, the operator should go back
to each hole, maximize the screen trace andmark the top of the trace on the surface of themonitor. This is repeated for all six traces andthe six points are then connected to form acurve on the screen that represents the DACcurve for that block and equipment being used.
Using a DAC Curve
Scanning is performed at a gain setting higherthan the reference level. This level is typicallydictated by a governing code or specification.When a screen trace is seen, the gain setting isset back to the reference level and the signal ismaximized. In most codes and specifications, anydiscontinuity that creates a screen trace at areference level that exceeds the distanceamplitude correction curve is rejectable. If themaximized signal is below DAC but is greaterthan 50 percent of DAC height, the indication isusually recorded and any signal greater than20 percent of DAC should be interrogated.These are general rules, and the operatorshould refer to the governing code orspecification to determine the actualrequirements. TNT
Jim Houf is Senior Manager of ASNT’s TechnicalServices Department and administers all ASNTcertification programs. (800) 222-2768 X212,(614) 274-6899 fax, <[email protected]>.
What Happens Here Goes Everywhere in the NDT Industry!
ASNT Fall Conference &Quality Testing Show 2004
The American Society for Nondestructive Testing invitesyou to attend the event where the full spectrum of NDTprofessionals from industry, technology and applicationmeet in an unsurpassed networking forum.
15–19 November 2004Las Vegas, NV, USA Riviera Hotel
To register and for program information visitwww.asnt.org or call 614.274.6003, 800.222.2768
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10 · 10/2004 · The NDT Technician
PRACTITIONERPROFILEAnthony J. Gatti, Sr.
A nthony Gatti is responsible for the inspection ofbabbitted bearings. If you aren’t familiar with theterm babbitt, it refers to a relatively soft, white
metal alloy composed of copper, antimony and a lot oftin. Babbitt metal is commonly used as the contactmaterial in bearing assemblies for large, high-speedshafts. The beauty of babbitt is that it has the capabilityof supporting heavy loads, has a long service life providedproper operating and lubrication conditions aremaintained, and, importantly, is soft enough so that it willnot damage shaft material. Babbitt in a bearing assemblyis analogous to the fuse in an electrical circuit. As the fuseis there to protect the circuit, the babbitt is there toprotect the bearing assembly. Should something run awry,it’s the babbitt that wears first. Tony Gatti has been anactive member of ASNT and the Greater PhiladelphiaSection for many years. He is also the new and very proudGrandpa of Madeline Christine.
How did you first become involved in NDT?
I’ve been employed here at Kingsbury, Inc. for thirty-nineyears. For the first 17 years, I was a machinist. Then Itransferred over to quality control and my interest in NDTstarted at that point. I was initially certified throughMagnaflux Quality Services for UT and UT Welding andthen again for PT and MT with the same organization. Forthe past 22 years, I’ve specialized in NDT work and I’vebeen certified in UT, PT, MT and soon VT.
Do you work in a lab or in the field?
Mainly, my work is here in Philadelphia in our corporateheadquarters. My employer is the leading manufacturerof babbitted fluid-film thrust and journal bearings for alltypes of rotating machinery. About 85 percent of ourwork is UT. We just bought another company that makesball and roller bearings. The product line is related butMT is heavily used for testing.
Is NDT done in a production environment or on anassembly line?
It’s far from an assembly line. We do have assembly,because there are a lot of intricate parts in our product,but at any point in time, when it calls for NDT — that isthe point of production where we do it. The parts caneither be brought to me or, if the part is too big, I go tothe part.
Can you describe your responsibilities in quality control?
My title is Level A, Inspector, Mechanical and I oversee theNDT work here. I have to have knowledge of machiningoperations, measuring equipment, complex blueprints,calibration procedures, government standards and audits.Our company is certified to ISO 9001:2000.
What are the indications you look for?
Babbitt is an antifriction metal that is about 88 to90 percent tin that is adhered to a base metal. After it’smachined and cut down, I inspectthe interface between the babbittmetal and the base metal withultrasonic testing to make sure thatthe two properly adhere. Parts thatI typically inspect can be anywherefrom 4 to 5 in. up to some that are122 in. These are fluid-film bearings(constructed to be self-lubricating)and there are a lot of componentsto these products with tolerancesthat range from 10ths of an inchdown to several thousandths of aninch. Geometry of the part has tobe considered and whether or notany machining was done — youhave to know all that. You can’t just slap some gel on andsay it’s good or bad.
Is every piece manufactured inspected and how much timedoes it take to test one piece?
If it’s steel, we can do a sample, unless dictated otherwiseby the customer’s contract. If it’s other components likechromium copper, then it’s automatic — it has to be done100 percent — every one. Once I set up, as an example, apart that’s 18 by 12 inches would probably take 10 to15 minutes. Shape is a factor and the surface has to becovered 100 percent. Given the shape of the part, I do theperimeter first all the way around. And then I pick a pointand begin scanning through the piece area by area.
What NDT projects have you found most interesting?
Using ultrasonic inspection, I’ve worked on all the mainpropulsion bearings for all of the Trident submarines, all ofthe journal bearings for all the CVN Nimitz class aircraftcarriers and I’ve worked on all the thrust and journal
10/2004 · The NDT Technician · 11
bearings for all of the DDG Arleigh Burke-Class guidedmissile destroyers — the USS Cole attacked by terrorists inAden, Yemen in 2000 is an example of this type ofdestroyer. Plus, I’ve worked on the units for two newturbines that were destined for Hoover Dam. That workwas done here in Philadelphia but, this past summer, mywife and I had an opportunity to make a tour of the damitself. We went all the way to the bottom — 720 feet —and we were walking around among the big turbines. Isaw the two turbines I had worked on. They even took mypicture there in front of them. When you’re at the bottomof the dam looking back up at it, and you see the 50 footdiameter pipes feeding these generators, it is just mind-boggling. They did this back in the 1930s nevertheless!
You’ve been an active member of ASNT for quite sometime and held various offices in the Greater PhiladelphiaSection as well as being the recipient of the Lou DiValerioTechnician of the Year Award in 2001. How has ASNTmembership been a benefit to you and how do you thinkit would benefit those interested in an NDT career?
I’m fortunate, my company has always supported myactivities in ASNT 100 percent and that has been a benefit
to me as far as learning NDT and helping me to advance.My membership has also been a benefit to my employer.I’ve made a lot of great contacts that I can call on when anNDT problem comes up. Fellow members have also calledon me for help with NDT questions.
What’s the worst part of NDT?
I guess sometimes if you get big quantities, and especiallyif you run into a problem, it can get tedious after a while.You have to stay focused, keep the right frame of mind tomake sure your interpretations are correct. Because, ifthey’re wrong at this stage, they’re scrap.
What’s the best part of NDT?
Well, the work itself; it’s good when you get everything togo right. But also, it’s the people I’ve met by being amember of ASNT and the camaraderie we’ve had.
What advice would you offer to one considering a careerin NDT?
If you’re gonna do it, do whatever it takes. TNT
INBOXQ: Number belts for pipe welds —what’s the best way to make themand how many should you have?J. Knapp, Seattle, WA
A: RT location marker tapes, or numbers lines, are commonlymade using duct tape and lead numbers. Here are the stepsrequired to make number belts or marker tapes:
Calculate or measure the circumference of the pipe. Keep inmind that nominal and actual pipe diameters are different forpipes under 14 in. in diameter. For example, an 8 in. diameterpipe (nominal) is actually 8.625 in., and a 12 in. (nominal) pipeis actually 12.75 in. So you must use the actual diameter whenyou calculate the circumference. For 14 in. pipe and larger,nominal and actual diameters are the same.
Decide if you want markers at the ends of each exposed filmor at regular intervals. Markers at the ends of film are mostcommon because fewer lead numbers are needed.
Next, decide what film size (4.5 in. x 10 in. or 4.5 in. x 17 in.)you’ll use for the pipe size, as this determines where markernumbers will be located. For film 10 in. long, numbers areusually placed every 8 in. on the tape, which allows an inch offilm overlap at each end. For film 17 in. long, they're at 15 in.
Tear off a strip of duct tape about 6 in. longer than thecalculated circumference and approximately 3 times as wide asyour lead letters are tall. Lay the duct tape out, adhesive sideup, on a flat surface next to an extended tape measure. At
one end, place a lead number zero (0) at the end of the tapeand adjacent to the end of the tape measure. The leadnumber should be along one edge of the duct tape stripbecause you will be folding the tape lengthwise over thenumbers when you are done. Continue to add numbers atrequired intervals until you reach the end of the tape. Somepeople use 0, 1, 2, 3, ..., others use the actual number ofinches from zero; this is often determined by the specificationor NDT procedure.
Carefully fold the tape over the lead numbers until you have afully wrapped numbers line the same length as thecircumference of the pipe. Finally, starting at the zero end, rollup the completed numbers line and mark it with the pipediameter it is intended for.
To use a numbers line, select the proper line for the pipe to beshot and unroll it. Use a short piece of duct tape to anchor thezero end to the pipe and wrap the rest around until the otherend overlaps zero. Tape that end down. You're ready to go.
If you're shooting really hot pipe, the heat can cause thenumbers line to stretch. If it stretches to the point where thenumbers are no longer under the cassette, you can always cutout a piece between each pair of numbers and retape thepieces together to extend the life of the line.
E-mail, fax or phone questions for Inbox to the Editor:[email protected]; phone (800) 222-2768 X 206;
ASNT is an International System of Units (SI) publisher providing unitsin SI as well as common units of measure.
1 in. = 2.54 cm
Volume 3, Number 4 October 2004
Publisher: Wayne HollidayPublications Manager: Paul McIntire
Editor: Hollis HumphriesTechnical Editor: Ricky L. Morgan
Review Board: William W. Briody, Bruce G. Crouse,Ed E. Edgerton, Anthony J. Gatti Sr., Jesse M. Granillo,Edward E. Hall, Richard A. Harrison, James W. Houf,Eddy Messmer, Raymond G. Morasse, Ronald T. Nisbet
The NDT Technician: A QuarterlyPublication for the NDT Practitioner(ISSN 1537-5919) is published quarterlyby the American Society forNondestructive Testing, Inc. The TNTmission is to provide information valuableto NDT practitioners and a platform fordiscussion of issues relevant to theirprofession. ASNT exists to create a safer world by promoting the professionand technologies of nondestructive testing.
IRRSP, Level III Study Guide, Materials Evaluation, NDT Handbook,Nondestructive Testing Handbook, The NDT Technician and www.asnt.orgare trademarks of The American Society for Nondestructive Testing, Inc.ACCP, ASNT, Research in Nondestructive Evaluation and RNDE are registeredtrademarks of the American Society for Nondestructive Testing, Inc.
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