As published in the February and March 2007 issues of Chemical Engineering Magazine
With regard to material of construction, the ongoing evolution of technology has raised expectations
throughout industry… William M. (Bill) Huitt
W. M. Huitt Co.
This is the first in a series of three articles that will
cover a wide range of piping topics. Topics that will cross
industry lines to include chemical, petroleum refining,
pharmaceutical, and other industries as well. It will be the
intent of these articles to address questions and
misunderstandings as they relate to industry on a general
basis.
“Pipe is pipe”. This is a euphemism (jargon if you will)
quite often used among piping designers and engineers.
Taken at face value, this is a true statement…pipe is
certainly pipe. However, taken in context, it means that no
matter which industry you work in when designing piping
systems it‟s all the same. And in that context it could not be
further from the truth.
The pharmaceutical industry, in its current state of
growth, is a relative new comer to design, engineering and
construction compared to the oil refining, bulk chemical,
pulp & paper and nuclear industries. As a frame of reference
the American Society of Mechanical Engineers (ASME) was
established in 1880; the American Petroleum Institute (API)
was established in 1919; 3-A Standards (for food & dairy)
were first developed in the 1920‟s; the ASME committee for
BPVC (Boiler Pressure Vessel Code) Section III for nuclear
power was proposed in 1963; Semiconductor Equipment and
Materials Institute (SEMI) was established in 1973; the
International Society of Pharmaceutical Engineers (ISPE)
was established in 1980; and ASME Biopharmaceutical
Equipment (BPE) issued its first Standard in 1997. Prior to
ASME-BPE much of the 3-A piping Standards were
plagiarized to facilitate design of pharmaceutical facilities.
While some of the above Standards Committees, and
their resulting Codes and Standards, are specific to a
particular industry others are more generalized in their use
and are utilized across the various industries.
As an example, Not only does the design and
construction of a large pharmaceutical facility require the
need for pharmaceutical based Standards, Codes, Guidelines
and Industry Practices such as those generated by ISPE and
ASME-BPE, it also requires those Standards created for
other industries as well. Meaning that, when designing and
constructing a bulk pharmaceutical finishing facility, or a
bulk Active Pharmaceutical Ingredient (API) facility the
engineers and constructors will also be working under some
of the same standards and guidelines as they would when
designing and building in other industries such as a
petroleum refinery or bulk chemical facility.
It is not that the pharmaceutical industry itself is young,
but the necessary engineering standards and practices are.
Within the past fifteen or so years, industry practice,
including dimensional standards for high purity fittings,
were left to the resources of the pharmaceutical Owner or
their engineering firm (engineer of record). The same applies
to construction methods and procedures, including materials
of construction. These requirements were basically
established for each project and were very dependent upon
Piping Design
Part 1: The Basics
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what the Owner‟s personnel and the engineering firm
brought to the table. Industry standards did not exist.
With regard to material of construction, the ongoing
evolution of technology has raised expectations throughout
industry, but even more so in the pharmaceutical,
biopharmaceutical and semiconductor industries.
For instance, out of the research and development that
went into the Hubble Space Telescope came new
methodology and technology to better measure and define
the all too tangible limits of surface roughness required in
material used in hygienic fluid service contact piping. This is
of particular interest to the pharmaceutical,
biopharmaceutical and semiconductor industries, where
cross-contamination at the molecular level cannot be
tolerated in many cases. This requires surfaces to be very
cleanable.
Surface roughness used to be expressed as polish
numbers (ie, #4 or #7) then grit numbers such as 150, 180 or
240). The problem with either of these two methods lay in
their subjectivity and their generality. These indicators were
not specific enough and the accept/reject result relied too
much on a subjective visual verification. There will be more
on surface finish requirements in Part II.
With acute awareness of the ongoing problems currently
faced in the pharmaceutical industry and, for altogether
different reasons, the semiconductor industry, various
Standards organizations have taken steps to alleviate the
consistent problems that have plagued the industry in the
past with high purity welding issues, standardization of
fittings, and guidelines for industry practice. We will discuss
some of the finer points of these issues and in some cases
what these Standards organizations, are doing to promote
and consolidate some of the better thinking in this industry
and in this field.
In these early paragraphs it seems as though I am
singling out the pharmaceutical industry as the focal point of
these discussions. As you will see this is not true. And in
saying pharmaceutical I do mean to include
biopharmaceutical (biopharm) as well.
In making an example of the pharmaceutical industry it
is simply an attempt on my part to utilize its relative
newness in the development of its own particular brand of
standards to give the reader a sense of standards
development and how these standards evolve.
This article and the two that follow will address metallic
piping topics including a discussion on hygienic piping.
While non-metallic piping is worthy of discussion it is too
broad a topic to try and capture here and will not be a part of
these articles. Some of the points that will be covered in this
and the following articles are topics such as:
1. ASME flange ratings, is it 150 and 300 pound
flange or is it Class 150 and Class 300 flange?
2. Does the 150, 300, etc. actually mean anything
or is it simply an identifier?
3. In forged fittings, is it 2000 pound and 3000
pound, or is it Class 2000 and Class 3000?
4. How do you determine which Class of forged
fitting to select for your specification?
5. Corrosion allowance in piping; how do you
determine and then assign corrosion
allowance?
6. How do you select the proper bolts and gaskets
for a service?
7. How is pipe wall thickness determined?
8. What is MAWP?
9. What is Operating and Design Pressure?
10. What is Operating and Design Temperature?
11. How do Design Pressure and Temperature
relate to a PSV set point and leak testing?
12. What Code should you be designing under?
13. What kind of problems can you expect with
sanitary clamp fittings?
14. How do you alleviate those problems with
sanitary clamp fittings?
15. What is ASME-BPE?
16. How does ASME B31.3 and ASME-BPE work
in concert with one another?
17. What is ASME BPE doing to bring
accreditation to the pharmaceutical Industry?
18. Design is the culmination and application of
industry standards and industry requirements
that take into account constructability along
with maintenance and operational needs. These
points will be covered as well.
We will first of all lay some groundwork by beginning
with the basics of general piping. By understanding the basic
elements of piping the designer and engineer can improve
their decision making in the material selection process and
system design effort. These articles will also make clear a
number of misconceptions with regard to terminology and
general practices.
What we will try to avoid is a lot of in-depth discussion
and elaborate analysis on specific points. What I would like
to achieve is a general discussion on many topics rather than
finite rhetoric on only a few.
With that said, this first article is entitled:
Piping Design Part I – The Basics
This article will not attempt to cover all of the various
types of piping components and joints that are available in
industry today. To keep the discussion focused we will
discuss only that segment of joints, fittings and components
most frequently used in general piping design.
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Neither will we duplicate the dialog of previous articles
that have provided excellent commentary on segments of
this same topic. Articles such as the one written by John C.
Cox and published by Chemical Engineering for their
January 2005 edition titled “Avoid Leakage in Pipe
Systems”. John provides a concise and descriptive narrative
on threaded and compression type connections. And the
article by Trinath Sahoo published by Chemical Engineering
for their June 2005 edition titled “Gaskets: The Weakest
Link”. In his article Trinath gives the reader some excellent
insight into the mechanics of gasket selection and design.
PIPE FLANGES
Pipe flanges are used to mechanically connect pipe
sections to other pipe sections, inline components, and
equipment. Flanges also allow pipe to be assembled and
disassembled without cutting or welding, eliminating the
need to issue a burn card for cutting and welding when
dismantling is required. In providing a breakable joint,
flanges unfortunately provide a potential leak path for the
service fluid contained in the pipe. Because of this, as in all
other joints, they need to be minimized where possible.
The most prevalent flange standards to be used in
industry are based on requirements of the American Society
of Mechanical Engineers (ASME) Standards. These include:
B16.1 – Cast Iron Pipe Flanges and Flanged Fittings,
B16.5 - Pipe Flanges and Flanged Fittings (NPS 1/2 through
NPS 24),
B16.24 – Cast Copper Alloy Pipe Flanges and Flanged
Fittings,
B16.36 – Orifice Flanges,
B16.42 – Ductile Iron Pipe Flanges and Flanged Fittings,
Large Diameter Steel Flanges (NPS 26 through NPS 60)
B16.47 – Large Diameter steel flanges (NPS 26 through
NPS 60) NPS, indicated above, is an acronym for Nominal Pipe Size.
Flanges are available with various contact facings (the
flange-to-flange contact surface) and methods of connecting
to the pipe itself. The flanges under B16.5 are available in a
variety of styles and pressure classifications. The different
styles, or types, are denoted by the way each connects to the
pipe itself and/or the type of face. The type of pipe-to-flange
connections consist of Threaded, Socket Welding (or Socket
Weld), Slip-On Welding (or Slip-On), Lapped (or Lap
Joint), Welding Neck (or Weld Neck), and Blind.
Threaded Flange
Figure 1
The Threaded flange, through Class 400, is connected to
threaded pipe in which the pipe thread conforms to ASME
B1.20.1. For threaded flanges in Class 600 and higher the
length through the hub of the flange exceeds the limitations
of ASME B1.20.1. ASME B16.5 requires that when using
threaded flanges in Class 600 or higher Schedule 80 or
heavier pipe wall thickness be used, and that the end of the
pipe be reasonably close to the mating surface of the flange.
Note that the term “reasonably close” is taken, in context,
from Annex A of ASME B16.5, it is not quantified.
In order to achieve this “reasonably close” requirement
the length of the thread has to be longer and the diameters of
the smaller threads become smaller than that indicated in
ASME B1.20.1. When installing Threaded flanges Class 600
and higher, ASME B16.5 recommends using power
equipment to obtain the proper engagement. Simply using
arm strength with a hand wrench is not recommended.
The primary benefit of threaded flanges is in eliminating
the need for welding. In this regard Threaded flanges are
sometimes used in high-pressure service in which the
operating temperature is ambient. They are not suitable
where high temperatures, cyclic conditions or bending
stresses can be potential problems.
Socketweld Flange
Figure 2
The Socketweld flange is made so that the pipe is
inserted into the socket of the flange until it hits the shoulder
of the socket. The Pipe is then backed away from the
shoulder approximately 1/16” before being welded to the
flange hub.
If the pipe were resting against the shoulder (This is the
flat shelf area depicted in Fig. 2 as the difference between
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diameters B and B2) of the socket joint during welding, heat
from the weld would expand the pipe longitudinally into the
shoulder of the socket forcing the pipe-to-flange weld area to
move. This could cause the weld to crack.
The Socketweld flange was initially developed for use
on small size, high-pressure piping in which both a back-
side hub weld and an internal shoulder weld was made. This
provided a static strength equal to the Slip-On flange with a
fatigue strength 1.5 times that of the Slip-On flange.
Because the two-welds were labor intensive it became
the practice to weld only at the hub of the flange. In doing
this it relegated the socketweld flange to be more frequently
used for small pipe sizes (NPS 2” and below) in non-high-
pressure, utility type service piping. The Socketweld flange
is not approved above Class 1500.
Slip-On Flange
Figure 3
Unlike the Socketweld flange, the Slip-On flange allows
the pipe to be inserted completely through its hub opening.
Two welds are made to secure the flange to the pipe. One
fillet (pronounced “fill-it”) weld is made at the hub of the
flange and a second weld is made at the inside diameter of
the flange near the flange face.
The end of the pipe is offset from the face of the flange
by a distance equal to the lesser of the pipe wall thickness or
1/4” plus approximately 1/16”. This is to allow for enough
room to make the internal fillet weld without damaging the
flange face.
The Slip-On flange is a preferred flange for many
applications because of its initial lower cost, the reduced
need for cut length accuracy and the reduction in end prep
time. However, the final installed cost is probably not much
less than that of a Weld Neck flange.
The strength of a Slip-On flange under internal pressure
is about 40% less than that of a Weld Neck flange. The
fatigue rate is about 66% less than that of a Weld Neck
flange. The Slip-On flange is not approved above Class
1500.
Lap Joint Flange
Figure 4
The Lap Joint flange requires a companion lap joint, or
Type A stub-end (ref. Fig. 5) to complete the joint. The
installer is then able to rotate the flange. This allows for
quick bolthole alignment of the mating flange during
installation without taking the extra precautions required
during prefabrication of a welded flange.
Their pressure holding ability is about the same as a
Slip-On flange. The fatigue life of a Lap Joint/stub-end
combination is about 10% that of a Weld Neck flange, with
an initial cost that is a little higher than that of a Weld Neck
flange.
The real cost benefit in using a Lap Joint flange
assembly is realized when installing a stainless steel or other
costly alloy piping system. In many cases the designer can
elect to use a stub-end specified with the same material as
the pipe, but use a less costly, e.g. carbon steel, Lap Joint
Flange. This prevents the need of having to weld a more
costly compatible alloy flange to the end of the pipe.
Just a quick word about stub-ends; they are actually
prefabricated or cast pipe flares that are welded directly to
the pipe. They are available in three different types: Type A,
(which is the lap-joint stub-end), Type B and Type C (ref.
Fig. 5).
Type A (Fig 5) is forged or cast with an outside radius
where the flare begins. This radius conforms to the radius on
the inside of the Lap-Joint flange. The mating side of the
flare has a serrated surface.
Type B (Fig. 5) is forged or cast without the radius
where the flare begins. It is used to accommodate the Slip-
On flange or Plate flange as a back-up flange.
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Type C (Fig 5) is fabricated from pipe using five
suggested methods indicated in ASME B31.3. The most
prevalent of these is the machine flare. This is done by
placing a section of pipe into a flaring machine, flaring the
end of the pipe and then cutting it to length.
As you can see in the assembly detail of Fig. 5, stub-end
types B & C have no radius at the flare while Type A does.
This allows it to conform to the Lap-Joint flange. Due to the
radius of the type A stub-end, a slip-on flange would have a
poor fit, creating non-uniform loading of the flare face as
well as an undesirable point load at the radius of the flare.
Weld Neck Flange
Figure 6
The reinforcement area of the Weld Neck flange
distinguishes it from other flanges. This reinforcement area
is formed by the added metal thickness, which tapers from
the hub of the flange to the weld end. The bore of the flange
needs to be specified in order to obtain the same wall
thickness at the weld end as the pipe it will be welded to.
This will give it the same ID bore as the pipe.
The Weld Neck flange is actually the most versatile
flange in the ASME stable of flanges. Much of its use is for
fitting-to-fitting fabrication in which the flange can be
welded directly to a fitting, such as an elbow, without the
need for a short piece of pipe, as would be required with a
Slip-On flange. It can be used in low-pressure, non-
hazardous fluid services as well as high-pressure, high-
cyclic and hazardous fluid services.
While the initial cost of the Weld Neck flange may be
higher than that of a Slip-On flange the installed cost
reduces that differential. And for conditions of possible high
thermal loading, either cryogenic or elevated temperatures,
the Weld Neck flange would be essential.
Blind Flange
Figure 7
While the Blind flange is used to cap off the end of a
pipeline or a future branch connection it is also used for
other purposes. It can be drilled and tapped for a threaded
reducing flange or machined out for a Slip-On reducing
flange. The reduced opening can be either on-center or
eccentric.
Flange Pressure Ratings
ASME B16.5 flange pressure ratings have been
categorized into material groupings. These groupings are
formulated based on both the material composition and the
process by which the flange is manufactured.
The available pressure Classifications under ASME
B16.5 are: 150, 300, 400, 600, 900, 1500 and 2500. The
correct terminology for this designation is Class 150, Class
300, etc. The term 150 pound, 300 pound, etc. is a carry over
from the old ASA (American Standards Association)
Classification. ASA is the precursor to the American
National Standards Institute (ANSI).
Taking a quick step back, ANSI was founded as a
committee whose responsibility was to coordinate the
development of standards and to act as a standards
traffic cop for the various organizations that develop
standards. Its basic function is not to develop standards,
but rather to provide accreditation of those standards
Originating as the American Engineering
Standards Committee (AESC) in 1918, ANSI had, over
its first ten years, outgrown its Committee status and in
1928 was reorganized and renamed as the American
Standards Association (ASA). In 1966 the ASA was
reorganized again under the name of the United States
of America Standards Institute (USASI). In 1969 ANSI
adopted its present name.
While the B16 and B31 Standards have previously
carried the ASA and ANSI prefix with its various
Standards titles ASME has always been the
administrative sponsor in the development of those
standards. In the 1970’s the prefix designation changed
to ANSI/ASME and finally to ASME.
Referring to ANSI B16.* or ANSI B31.* is no
longer correct. Instead it is correct to refer to a
standard as ANSI/ASME B16.* in that it indicates an
Figure 5
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ANSI accredited ASME standard. Or you can simply
refer to the standard as ASME B16.* or ASME B31.*.
Development of ASME B16.5 began in 1920. In 1927
the American Tentative Standard B16e was approved. This
eventually became what we know today as ASME B16.5.
Until the 1960‟s the pressure Classifications, as addressed
earlier, were referred to as 150 pound, 300 pound, etc. It
was at this point the pressure Classification was changed to
the Class designation. These designations have no direct
correlation with pounds of pressure. Rather, they are a factor
in the pressure rating calculation found in B16.5. In Part II
of this series, we will discuss how these designations are
factored into the design of the flange.
Flange Pressure Ratings
Flanges, whether manufactured to ASME (American
Society of Mechanical Engineers), API (American
Petroleum Institute), MSS (Manufacturers Standardization
Society), AWWA (American Water Works Association) or
any other Standard, are grouped into pressure ratings. In
ASME these pressure ratings are a sub-group of the various
material groups designated in B16.5.
Figure 8 represents one of the Tables from the Table 2
series in ASME B16.5. This is a series of Tables that lists
the Working Pressures of flanges based on material
groupings, temperature and Classification.
There are 34 Tables segregated into three material
Categories of Carbon and low alloy steels, austenitic
stainless steels, and nickel alloys. These are further
segregated into more defined material sub-groups. Figure 8
shows Table 2-1.1, which indicates, in reverse sequence,
sub-category 1 of material group 1 (carbon and low alloy
steels).
If you had an ASME B16.5, Class 150, ASTM A105
flange this is the table you would use to determine the
Working Pressure limit of the flange. To find the Working
Pressure of the above mentioned flange enter the column of
this table designated as 150 then move down the column to
the operating temperature. For intermediate temperatures,
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linear interpolation is permitted.
In the previous paragraph you will notice that I
indicated “operating temperature” when looking to
determine the Working Pressure of a flange. „Operating‟ and
„working‟ are synonymous. The indication of a working
pressure and temperature of a fluid service is the same as
indicating the operating pressure and temperature.
There exists some confusion in this area. That confusion
becomes apparent when the engineer is determining design
pressure and temperature and applying that to the flange
rating. On the surface there appears to be a conflict between
rating a flange for design conditions when Table 2 only
indicates working pressures.
Operating and design pressures and temperatures will be
explained in more detail in Article 2. For now I will explain
that every service should have an operating
pressure/temperature and a design pressure/temperature. A
design condition is the maximum coincidental pressure and
temperature condition that the system is expected or allowed
to see. This then becomes the condition to which you should
design for, and to which the leak test is based on, not the
operating condition.
Tables 2, as it indicates, represents the working or
operating pressures of the flange at an indicated temperature
for a specific Class. The maximum hydrostatic leak test
pressure for a Class 150 flange in Table 2-1.1 is 1.5 times
the rated working pressure at 100°F, or 285 x 1.5 = 427.5
rounded off to the next higher 25 psi, or 450 psig.
We can extrapolate that piece of information to say that
since hydrostatic leak test pressure is based on 1.5 x design
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pressure the working pressure limit given in the Table 2
matrix ostensibly becomes the design pressure limit.
When working with ASME B31.3 Category D fluid
services, and initial service leak testing is performed, the
working pressure limit then remains the working pressure
limit because testing is performed at operating or working
pressures. In saying that however, there are caveats that
address the fact that not all Category D fluid services should
waive the hydrostatic leak test for an initial service leak test.
These conditions, such as steam service, will also be
discussed in a subsequent article.
Category D fluid services are those fluid services that
are nonflammable, nontoxic and not damaging to human
tissue. Category D fluids additionally do not exceed 150 psig
and 366º F.
In initial service leak testing the test fluid is the service
fluid. Leak testing occurs during or prior to initial operation
of the system. As the service fluid is introduced to the piping
system and brought to operating pressure, in pressure
increments, all joints are observed for possible leaks. If no
leaks are detected the pipeline simply remains in service.
Other ASME B31.3 fluid services may be expected to
operate at one set of conditions, but are designed for another
set. For those systems, which might include periodic steam-
out (cleaning, sterilization, sanitization) or passivation, you
therefore want to base your flange rating selection on those
more extreme, periodic design conditions. To clarify
periodic in this context, the sanitization process can be done
as frequently as once per week and last for one to one and
half shifts in duration.
Flange Facing & Surface Finishes
Standard flange facing designations (ref. Fig. 9) are as
follows: Flat Face, Raised Face, Ring Joint, Tongue and
Groove, Large and Small Male and Female, Small Male and
Female (on end of pipe), Large and Small Tongue and
Groove. The height of the raised face for Class 150 and 300
flanges is 0.06”. The height of the raised face for Class 400
and above is 0.25”.
Across industry, not discounting the lap-joint flange and
stub-end combination, the two most widely used flange
facings are the flat face and the raised face.
The surface finish of standard raised face and flat face
flanges has a serrated concentric or serrated spiral surface
finish with an average roughness of 125 μin to 250 μin. The
cutting tool used for the serrations will have a 0.06 in. or
larger radius and there should be from 45 to 55 grooves per
inch.
BOLTS, NUTS & GASKETS
Sealing the flange joint, and as you will see further in
this article, the hygienic clamp joint, is paramount in
providing integrity to the overall piping system. This is
achieved with the use of bolts, nuts and gaskets. Making the
right selection for the application can mean the difference
between a joint with integrity and one without.
ASME B16.5 provides a list of appropriate bolting
material for ASME flanges. The bolting material is grouped
into three strength categories; high, intermediate and low,
which are based on the minimum yield strength of the
specified bolt material.
The High Strength category includes bolt material with
a minimum yield strength of not less than 105 ksi. The
Intermediate Strength category includes bolt material with a
minimum yield strength of between 30 ksi and 105 ksi. The
Low Strength category includes bolt material with a
minimum yield strength no greater than 30 ksi.
As defined in ASME B16.5, the High Strength bolting
materials "…may be used with all listed materials and all
gaskets". The Intermediate Strength bolting materials
"…may be used with all listed materials and all gaskets,
provided it has been verified that a sealed joint can be
maintained under rated working pressure and temperature”.
The Low Strength bolting materials "…may be used with all
listed materials but are limited to Class 150 and Class 300
joints", and can only be used with selected gaskets as
defined in ASME B16.5.
ASME B31.3 further clarifies in para. 309.2.1, "Bolting
having not more than 30 ksi specified minimum yield
strength shall not be used for flanged joints rated ASME
B16.5 Class 400 and higher, nor for flanged joints using
metallic gaskets, unless calculations have been made
showing adequate strength to maintain joint tightness".
B31.3 additionally states in para. 309.2.3, “…If either flange
is to the ASME B16.1 (cast iron), ASME B16.24 (cast
copper alloy), MSS SP-42 (valves with flanged and buttweld
ends), or MSS SP-51 (cast flanges and fittings)
specifications, the bolting material shall be no stronger than
low yield strength bolting unless: (a) both flanges have flat
faces and a full face gasket is used: or, (b) sequence and
torque limits for bolt-up are specified, with consideration of
sustained loads, displacement strains, and occasional loads
(see paras. 302.3.5 and 302.3.6), and strength of the flanges.
In specifying flange bolts, as well as the gasket, it is
necessary, not only to consider design pressure and
temperature, but fluid service compatibility, the critical
nature of the fluid service and environmental conditions all
in conjunction with one another.
To better understand the relationship of these criteria I
will list and provide some clarification for each:
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1. The coincident of design pressure and temperature
is what determines the pressure Class of a flange
set. That, in turn, along with flange size, will
determine the number and size of the flange bolts.
The flange Class will also determine the
compressibility range of the gasket material.
2. Fluid service compatibility will help determine the
gasket material.
3. The critical nature of the fluid will determine the
degree of integrity required in the joint. This will
help determine bolt strength and material as well as
gasket type.
4. Environmental conditions will also help determine
bolt material (Corrosive atmosphere, wash-down
chemicals, etc.).
What this ultimately means is that all of the variables
that come together in making up a flange joint have to do so
in a complementary fashion. Simply selecting a gasket based
on material selection and not taking into account the
pressure rating requirement could provide a gasket that
would get crushed under necessary torque requirements
rather than withstand the bolt load and create a seal.
Selecting a low strength bolt to be used with a Class 600
flange joint with proper gasketing will require the bolts to be
torqued beyond their yield point, or at the very least beyond
their elastic range. To explain this briefly; bolts act as
springs when they are installed and loaded properly. In order
for the flange joint to maintain a gasket seal it requires
dynamic loading. Dynamic loading of flange bolts allows
expansion and contraction movement in and around the joint
while maintaining a seal. This is achieved by applying
sufficient stress to the bolt to take it into the material‟s
elastic range.
If the bolts are not stressed sufficiently into their elastic
range any relaxation in the gasket could reduce the sealing
ability of the joint. To the other extreme, if the bolts were
stressed beyond their elastic range and into the plastic range
of their material of construction the same issue applies, they
will lose their dynamic load on the gasket. In this case, if
they do not shear they will take a set. Any relaxation in the
gasket will then result in the reduction or elimination of the
joints sealing ability.
With regard to the nut, it should be selected to
compliment the bolt. Actually the bolt material specification
will steer you, either partially or completely, into the proper
nut selection.
ASTM A307, a material standard for bolts in the low-
strength category, states that the proper grade for bolts to be
used for pipe flange applications is Grade B. A307 goes
further to state that when used for pipe flanges Grade B bolts
require a Heavy Hex Grade A nut under ASTM A563. In
writing a pipe spec that includes the A307 bolt you would
not need to specify the nut since it is already defined in
A307.
However, ASTM A193, alloy and stainless steel bolts,
goes only so far when it states that nuts shall conform to
ASTM A194, but there are several grades of A194 nuts to
select from. This is an example of where the matching nut is
not always explicitly called out in the ASTM Standard.
Because the ASTM Standards are inconsistent in that regard
the spec-writer must make sure it is covered in a
specification.
You can see from this bit of information that all four
components, flanges, bolts, nuts and gaskets have to be
selected in conjunction with one another in order for the
joint assembly to perform in a way that it is expected to for a
given application.
Pipe, Tube & Fittings
One of the big differences between pharmaceutical and
semi-conductor piping and other industrial piping, is the
requirements of high purity, or hygienic fluid services.
These requirements, as dictated by current Good
Manufacturing Practices (cGMP) and defined and quantified
by the ISPE and ASME-BPE, are stringent with regard to the
manufacture, documentation, fabrication, installation,
qualification, validation and quality control of hygienic
piping systems and components.
The man-hours required in generating, maintaining and
controlling the added documentation required for hygienic
fabrication and installation is in the range of 30% to 40% of
the overall cost of fabrication and installation. Part II in this
series will get more into the requirements of hygienic
fabrication and where that added cost comes from.
For now we will stay with general pipe and fittings. In
an attempt at keeping this article concise we will only cover
those fittings that are predominantly used throughout
industry, both in process and in utility services.
Pipe fittings are manufactured by the following
processes: cast, forged and wrought.
Cast Fittings
Cast fittings are provided in cast iron, malleable iron,
steel, stainless steel, brass, bronze, and other alloy material
as follows:
Cast Iron: Cast iron threaded fittings, under ASME
B16.4, are available in Class 125 and Class 250 for sizes
NPS 1/4” through 12”. Cast iron flanged fittings, under
ASME B16.1, are available in Class 25, 125 and 250 in sizes
NPS 1” through 48”.
Malleable Iron: Malleable iron fittings, under ASME
B16.3, are available in Class 150 and Class 300 in sizes NPS
10
1/8” though 6” for Class 150 and 1/4” through 3” for Class
300.
It needs to be noted here that Classifications such
as 150 and 300 are not universal throughout the ASME
Standards. They are specific to the Standard that they
are associated with. You cannot automatically transfer
the pressure/temperature limits of a flange joint in
ASME B16.5 to that of a fitting in B16.3.
Cast Steel: Cast steel, stainless steel and alloy steel
flanged fittings, under ASME B16.5, are available in Class
150, 300, 400, 600, 900, 1500 & 2500 in sizes 1/2” though
24”.
Cast Brass: Cast Brass and bronze threaded fittings,
under ASME B16.15, are available in Class 125 and 250, in
sizes NPS 1/8” through 4” for Class 125 and 1/4” through 4”
for Class 250.
Cast Copper: Cast copper solder joints, under ASME
B16.18, are available in sizes 1/4” through 6”.
Forged Fittings
Before getting into forged fittings I would like to
explain the difference between forged and wrought fittings.
There seems to be some vague misconception of what the
term forged means and what the term wrought means and
how it applies to pipe fittings.
The term forging actually comes from the times when
metal was worked by hand. A bar of steel would be placed
into a forge and heated until it reached its plastic state, at
which time the metal would be pulled out of the forge and
hammered into some desired shape. Today forging metal
basically means working the metal by means of hydraulic
hammers to achieve the desired shape.
As a small bit of trivia, up until the late 1960‟s, when
mills stopped producing it, wrought iron was the choice of
ornamental iron workers. It is still produced in Europe, but
most of what we see manufactured as wrought iron in the
U.S. is actually various forms of steel made to look like
wrought iron.
True wrought iron is corrosion resistant, has excellent
tensile strength, welds easily and in its plastic range is said
to be like working taffy candy. What gives wrought iron
these attributes is the iron silicate fibers, or “slag” added to
the molten iron with a small percentage of carbon, whereas
cast iron, with a high carbon content, is more brittle and not
as easily worked.
The smelters, where the iron ore was melted to produce
wrought iron, were called bloomeries. In a bloomery the
process does not completely melt the iron ore, rather the
semi-finished product was a spongy molten mass called a
bloom, derived from the red glow of the molten metal,
which is where the process gets its name. The slag and
impurities were then mechanically removed from the molten
mass by twisting and hammering which is where the term
wrought originates.
Today forged and wrought are almost synonymous. If
we look in ASTM A234 - Standard Specification for Piping
Fittings of Wrought Carbon Steel and Alloy Steel for
Moderate and High Temperature Service we can see in Para
4.1 and in Para 5.1 that wrought fittings made under A234
are actually manufactured or fabricated from material pre-
formed by one of the methods listed previously, which
includes forging. In ASTM A961 - Standard Specification
for Common Requirements for Steel Flanges, Forged
Fittings, Valves and Parts for Piping Applications the
definition for the term Forged is, “the product of a
substantially compressive hot or cold plastic working
operation that consolidates the material and produces the
required shape. The plastic working must be performed by a
forging machine, such as a hammer, press, or ring rolling
machine, and must deform the material to produce a
wrought structure throughout the material cross section.”
The difference therefore between forged and wrought
fittings is that forged fittings, simply put, are manufactured
from bar, which while in its plastic state is formed into a
fitting with the use of a hammer, press or rolling machine.
Wrought fittings, on the other hand, are manufactured from
killed steel, forgings, bars, plates and seamless or fusion
welded tubular products that are shaped by hammering,
pressing, piercing, extruding, upsetting, rolling, bending,
fusion welding, machining, or by a combination of two or
more of these operations. In simpler terms wrought signifies
“worked”. There are exceptions in the manufacture of both,
but that is the general difference.
Something worth noting at this point concerns the
ASTM specifications. In quoting from ASTM A961 I was
quoting from what ASTM refers to as a General
Requirement Specification, which is what A961 is. A
General Requirement Specification is a specification
that covers requirements that are typical for multiple
individual Product Specifications. In this case the
individual Product Specifications covered by A961 are
A105, A181, A182, A360, A694, A707, A727 and A836.
The reason I point this out is that many designers
and engineers are not aware that when reviewing an
A105 or any of the other ASTM individual Product
Specifications you may need to include the associated
General Requirement Specification in that review.
Reference to a General Requirement Specification can
be found in the respective Product Specification.
Forged steel and alloy steel socketweld and threaded
fittings, under ASME B16.11, are available in sizes NPS
1/8” through 4”. Forged socketweld fittings are available in
pressure rating Classes 3000, 6000 and 9000. Forged
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threaded fittings are available in pressure rating Classes
2000, 3000 and 6000.
What I see quite often, and this includes all of the
industries I have been associated with, is a misapplication of
pressure rating in these fittings. This leads me to believe that
the person specifying components does not fully understand
the relationship between the pressure Class of these fittings
and the pipe they are to be used with.
In ASME B16.11 is a table that associates, as a
recommendation, fitting pressure Class with pipe wall
thickness, as follows:
Table 1 – Correlation of Pipe Wall Thickness & Pressure Rating
Pipe Wall Thk. Threaded Socketweld
80 or XS 2000 3000
160 3000 6000
XXS 6000 9000
The ASME recommendation is based on matching the
I.D. of the barrel of the fitting with the I.D. of the pipe. The
shoulder of the fitting (the area of the fitting that the end of
the pipe butts against), either socketweld, as shown in Fig.
10, or threaded, is approximately, allowing for fabrication
tolerances, the same width as the specified mating pipe wall
thickness.
Figure 10 – Socket Weld Fitting Joint from ASME B16.11
As an example, referring to Table 1, if you had a
specified pipe wall thickness of Sch. 160 the matching
threaded forged fitting would be a Class 3000, for
socketweld it would be a Class 6000. The fitting pressure
Class is selected based on the pipe wall thickness. Referring
to Fig. 10, you can readily see that by not matching the
fitting Class to the pipe wall thickness it will create either a
recessed area or a protruding area the length of the barrel of
the fitting, depending on which side you error on. For forged
reinforced branch fittings refer to MSS Standard SP-97 –
Integrally Reinforced Forged Branch Outlet Fittings -
Socket Welding, Threaded and Buttwelding Ends.
Wrought Fittings
Wrought Steel Butt Weld Fittings under ASME B16.9
(standard radius 1.5D elbows and other fittings) are available
in sizes 1/2” through 48”. Wrought Steel Butt Weld Fittings
under B16.28 (short radius 1D elbows), are available in sizes
1/2” through 24”. There is no pressure/temperature rating
classification for these fittings. In lieu of fitting pressure
classifications both B16.9 and B16.28 require that the fitting
material be the same as or comparable to the pipe material
specification and wall thickness. Under ASME B16.9, given
the same material composition, the fittings will have the
same allowable pressure/temperature as the pipe. ASME
requires that the fittings under B16.28, short radius elbows,
be rated at 80% of that calculated for straight seamless pipe
of the same material and wall thickness.
These fittings can be manufactured from seamless or
welded pipe or tubing, plate or forgings. Laterals, because of
the elongated opening cut from the run pipe section are rated
at 40% of that calculated for straight seamless pipe of the
same material and wall thickness. If a full strength lateral is
required either the wall thickness of the lateral itself can be
increased or a reinforcement pad can be added at the branch
to compensate for the loss of material at the branch opening.
Wrought copper solder joint fittings, under ASTM B88
and ASME B16.22, are available in sizes 1/4” through 6”.
These fittings can be used for brazing as well as soldering.
The pressure/temperature rating for copper fittings are
based on the type of solder or brazing material and the
tubing size. It will vary too, depending on whether the fitting
is a standard fitting or a DWV (Drain, Waste, Vent) fitting,
which has a reduced pressure rating.
As an example, using alloy Sn50, 50-50 Tin-Lead
Solder, at 100ºF, fittings 1/2” through 1” have a pressure
rating of 200 psig and fittings 1½” through 2” have a
pressure rating of 175 psig. DWV fittings 1½” through 2”
have a pressure rating of 95 psig.
Using alloy HB, which is a Tin-Antimony-Silver-
Copper-Nickel (Sn-Sb-Ag-Cu-Ni) solder, having 0.10%
maximum Lead (Pb) content, at 100ºF, fittings 1/2” through
1” have a pressure rating of 1035 psig and fittings 1½”
through 2” have a pressure rating of 805 psig. DWV fittings
1½” through 2” would have a pressure rating of 370 psig.
As you can see, within the same type of fitting, there is
a significant difference in the pressure ratings of soldered
joints depending on the type of filler metal composition.
Much of the difference is in the temperature at which the
solder or brazing filler metal fully melts. This is referred to
as its liquidus state. The temperature at which it starts to
melt is referred to as its solidus temperature, the higher the
liquidus temperature the higher the pressure rating of the
joint.
Pipe and Tubing
The catch-all terminology for pipe and tubing is tubular
products. This includes pipe, tube and their respective
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fittings. Piping itself refers to a system of pipe, fittings,
flanges, valves, bolts, gaskets and other in-line components
that make up an entire system used to convey a fluid. The
simple distinction between pipe and tubing is that tubing is
thin-walled pipe with a different size for size diameter.
Tubular products can basically be grouped into three
broad classifications: pipe, pressure tube and mechanical
tube.
Based on user requirements the above classifications
come in various types such as Standard Pipe, Pressure Pipe,
Line Pipe, Water Well Pipe, Oil Country Tubular Goods,
Conduit, Piles, Nipple Pipe and Sprinkler Pipe. The two
types that we are mainly interested in are Standard and
Pressure Pipe. Distinguishable only from the standpoint of
use, Standard Pipe is intended for low pressure, non-volatile
use, whereas Pressure Pipe is intended for use in higher
integrity services. These are services in which the pipe is
required to convey high pressure volatile or non-volatile
liquids and gases at sub-zero or elevated temperatures.
The following represents a combined description of
Standard and Pressure Pipe.
Pipe: Pipe is manufactured to a NPS in which the OD
of a given nominal size remains constant while any change
in wall thickness is reflected in the pipe ID. Pipe wall
thicknesses are specified by Schedule (Sch.) numbers 5, 10,
20, 30, 40, 60, 80, 100, 120, 140 and 160. Add the suffix „s‟
when specifying stainless steel or other alloys. Wall
thickness is also specified by the symbols Std. (Standard),
XS (Extra Strong) and XX (Double Extra Strong).
Pipe NPS 12” and smaller has an OD that is nominally
larger than that specified. Pipe with a NPS 14” and larger
has an OD equal to the size specified.
Tubing: Steel and alloy tubing is manufactured to an
OD equal to that specified. Meaning that 1/4” tubing will
have a 1/4” OD, 2” tubing will have a 2” OD. Copper
tubing, accept for ACR (Air-Conditioning & Refrigeration)
tubing, which has an OD equal to that specified, has an OD
that is always 1/8” larger than the diameter specified. As an
example, 1/2” tubing will have a 5/8” OD, 1” tubing will
have a 1 1/8” OD.
Wall thickness for tubing is specified in the actual
decimal equivalent of its thickness.
Pipe is manufactured in three basic forms: cast, welded
and seamless. Tubing is manufactured in two basic forms:
welded and seamless.
Cast Pipe: Cast pipe is available in four basic types:
white iron, malleable iron, gray iron and ductile iron. White
iron has a high carbon content in the carbide form. The lack
of graphite gives it its light colored appearance. Carbides
give it a high compressive strength and a hardness that
provides added resistance to wear, but leave it very brittle.
Malleable iron is white cast iron that has been heat
treated for added ductility. By reheating white cast iron in
the presence of oxygen containing materials such as iron
oxide, and allowing it to cool very slowly, the free carbon
forms small graphite particles. This gives malleable iron
excellent machinability and ductile properties along with
good shock resistant properties.
Gray iron is the oldest form of cast iron pipe and is
synonymous with the name cast iron. It contains carbon in
the form of flake graphite, which gives it its gray identifying
color. Gray cast iron has virtually no elastic or plastic
properties, but has excellent machining and self-lubricating
properties due to the graphite content
Ductile iron is arguably the most versatile of the cast
irons. It has excellent ductile and machinable properties
while also having high strength characteristics.
Welded Steel Pipe and Tubing: Referring to pipe in
the following also includes tubing.
Welded steel pipe is manufactured by Furnace Welding
or by Fusion Welding. Furnace Welding is achieved by
heating strip steel, also referred as skelp, to welding
temperature then forming it into pipe. The continuous weld,
or buttweld, is forged at the time the strip is formed into
pipe. This is a process generally used to manufacture low
cost pipe 3 ½” and below.
Fusion Welded pipe is formed from skelp that is cold
rolled into pipe and the edges welded together by resistance
welding, induction welding or arc welding. Electric
resistance welding (ERW) can be accomplished by flash
welding, high-frequency or low-frequency resistance
welding. A scarfing tool is used to remove upset material
along the seam of flash-welded pipe.
Flash welding produces a high strength steel pipe in
NPS 4” through 36”. Low-frequency resistance welding can
be used to manufacture pipe through NPS 22”. High-
frequency resistance welding can be used to manufacture
pipe through NPS 42”.
High-frequency induction welding can be used for high
rate production of small NPS pipe. This is a cleaner form of
welding in which scarfing, or the cleaning of upset material
along the seam, is normally not required.
Arc welding the longitudinal seam of production pipe is
accomplished with submerged arc welding (SAW), inert gas
tungsten arc welding (GTAW) also called tungsten inert gas
welding (TIG), or gas shielded consumable metal arc
welding (MIG).
13
As you will see in Part II, the type of weld seam used in
the manufacture of pipe is a factor when calculating the
Pressure Design Thickness (t) of the pipe wall. It reduces the
overall integrity of the pipe wall by a percentage given in
ASME B31.3 based on the type of longitudinal seam weld.
Seamless Steel Pipe and Tubing: Referring to pipe in
the following also includes tubing.
Seamless steel pipe, using various extrusion and
mandrel mill methods, is manufactured by first creating a
tube hollow from a steel billet, which is a solid steel round.
The billet is heated to its hot metal forming temperature then
pierced by a rotary piercer or by a press piercer creating the
tube hollow, which will have a larger diameter and thicker
wall than its final pipe form. The tube hollow is then hot-
worked by the Mandrel Mill Process, Mannesmann Plug-
Mill Process, or Ugine Sejournet Extrusion Process.
Upon completion of these processes the pipe is referred
to as hot-finished. If further work is required to achieve
more accuracy in the diameter, wall thickness or improve its
finish the pipe can be cold-finished, or cold-worked. When
the pipe is cold-finished it will require heat treating to
remove stress in the pipe wall created when worked in its
cold state.
There are also two forging processes used in the
manufacture of large diameter (10 to 30 inch) pipe with
heavy wall thickness (1.5 to 4 inch). The two forging
methods are called Forged and Bored, and Hollow Forged.
Other Material and Systems
We have touched on just some of the key points of steel
pipe and fittings. What I have not touched on are plastic
lined pipe systems and non-metallic piping including
proprietary piping systems. The area of non-metallic piping
is certainly worth including in the context of piping.
However, we will keep these articles focused on metallic
piping material. Non-metallic piping merits a discussion on
its own, and should not be relegated to a paragraph or two
here.
However, since plastic lined pipe is steel pipe with a
liner and is so widely used in the various industries I will
touch on some of its key points.
Lined Pipe Systems: Lined flex hoses were first
developed in 1936 by Resistoflex followed by lined pipe,
which did not come to the industry until 1956 by way of the
same company. When first introduced, plastic line pipe filled
a large fluid handling gap in industry, but brought with it
some technical issues.
As other manufacturers such as Dow and Peabody
Dore‟ began producing lined pipe and fittings industry
standards for lined pipe did not exist. Consequently, there
were no standard fitting dimensions and the availability of
size and type of fittings would vary from one company to
another, and still, to a much lesser degree, does to this day.
Due to the autonomous nature of lined pipe
manufacturing during its initial stages the pipe designer
would have to know early in the design process which
manufacturer they were going to use. Particularly in fitting
make-up situations, you needed to know in advance what
those make-up dimensions were going to be, and thus the
fitting manufacturer.
While not having industry standard dimensions was a
design problem other operational type problems existed as
well. Some of the fluid services these line pipe systems were
specified for, and still are, would normally be expected to
operate under a positive pressure, but at times would phase
into a negative pressure. The liners in these early systems
were not necessarily vacuum rated and at times would
collapse under the negative internal pressure, plugging the
pipeline.
There was an added problem when gaskets were thrown
into the mix. Gaskets were not normally required unless
frequent dismantling was planned, and many firms, both
engineers and manufacturers, felt more secure in specifying
gaskets at every joint. When required, the gasket of choice,
in many cases, was an envelope type gasket made of PTFE
(polytetrafluoroethylene) with an inner core of various filler
material,Viton (a DuPont trade name) or EPDM.
These gaskets had a tendency to creep under required
bolt torque pressure at ambient conditions. From the time a
system was installed to the time it was ready to hydrotest the
gaskets would, on many occasion, creep, or relax to the point
of reducing the compressive bolt load of the joint enough to
where it would not stand up to the hydrotest pressure. Quite
often leaks would become apparent during the fill cycle prior
to testing.
There also exists the problem of permeation with regard
to PTFE liner material and of Internal and External
Triboelectric Charge Generation and Accumulation (static
electricity). But, due to the diligent efforts of the line pipe
and gasket industries these types of problems have either
been eliminated or controlled, and some are still being
pursued.
Fitting dimensions have been standardized through
ASTM F1545 in referencing ASME B16.1 (cast iron
fittings), B16.5 (steel fittings) and B16.42 (ductile iron
fittings). You will need to read Note 3 under Sub-Para. 4.2.4,
which states, “Center-to-face dimensions include the plastic
lining.” Meaning, the dimensions given in the referenced
ASME standards are to the bare metal face of the fittings.
However, when lined fittings are manufactured the metal
casting is modified to accommodate the liner thickness being
included in that same specified center-to-face dimension.
14
With regard to vacuum rating, liner specifications are
greatly improved, but you will need to check the vacuum
ratings of available pipe and fittings with each tentative
manufacturer. This provision will vary from manufacturer to
manufacturer depending on size, fitting, liner type, pressure
and temperature.
Gasket materials such as Garlock‟s Gylon gasket, which
is a PTFE/Silicate composite, and W. L. Gore‟s Universal
Pipe Gasket, which is a 100% expanded PTFE, have been
developed to reduce the creep rate in a gasket material that is
compatible with virtually the same fluid services that lined
pipe systems are usually selected for.
Permeation issues with PTFE liners (it also exists, to a
lesser extent, with other liner material) have been
accommodated more than resolved with the use of vents in
the steel pipe casing, the application of vent components at
the flange joint, and increased liner thickness.
Internal and external charge accumulation, known as
static electricity, or triboelectric charge accumulation, is the
result of an electrical charge generation unable to dissipate.
If the electrical charge generation is allowed to continually
dissipate to ground then there is no charge build-up and no
problem. This is what occurs with steel pipe in contact with
a flowing fluid. Charge generation has a path to ground and
does not have an opportunity to build up.
With regard to thermoplastic lined pipe there are two
issues to be considered: external charge accumulation and
internal charge accumulation.
This is an issue that requires experience and expertise in
order to analyze a particular situation. What we will do in
Part II of this series is provide you with basic information
that will at least allow you to be familiar with the subject,
and help you to understand the issues.
Standard sizes of plastic lined pipe and fittings range
from NPS 1” through 12”. Edlon, a lined pipe manufacturer,
also manufactures larger diameter pipe and fittings from
NPS 14” through 24”, and when requested can manufacture
spools to 144” diameter.
Hygienic Piping
Hygienic is a term defined in ASME-BPE as: “of or
pertaining to equipment and piping systems that by design,
materials of construction, and operation provide for the
maintenance of cleanliness so that products produced by
these systems will not adversely affect animal or human
health.”
While system components such as tube, fittings, valves
and the design itself, with regard to hygienic conditions, can
translate to the Semi-Conductor industry the term hygienic
does not. It pertains strictly to the health aspects of a clean
and cleanable system for the pharmaceutical industry. The
semi-conductor industry requires a high, or in some cases
higher, degree of cleanliness and cleanability than hygienic
systems in the pharmaceutical industry, for altogether
different reasons.
A term that can more appropriately be interchanged
between these two industries is high-purity. This implies a
high degree of cleanliness and cleanability without being
implicitly connected with one industry or the other.
For what is referred to as product contact material, the
surface roughness, dead-leg minimums and an easily
cleanable system are all imperative. Because of this the
pharmaceutical industry had to make a departure from the 3-
A standards it plagiarized early on in order to develop a set
of guidelines and standards that better suit its industry. Enter
ASME-BPE.
ASME-BPE has taken on the task of providing a forum
for engineers, pharmaceutical manufacturers, component and
equipment manufacturers, and inspectors in an effort to
develop consensus standards for the industry where none
existed before. I won‟t go further with this except to say that,
to the handful of engineers undaunted by the task ahead of
them, in approaching ASME about the need to create
another standards committee, and the perseverance to see it
through; my hat goes off to you.
Hygienic piping was, up until just recently, referred to
as sanitary piping. Because this term has been so closely
associated with the plumbing industry and sanitary drain
piping it is felt by the pharmaceutical industry that the
change in terminology to hygienic is more appropriate.
In both the pharmaceutical and semiconductor industries
the need for crevice free, drainable systems is a necessity.
This translates into weld joint quality, mechanical joint
design requirements, interior pipe surface roughness limits,
system drainability and dead-leg limitations.
Slope, welding, dead-legs and surface roughness will be
discussed in Part II. This article will concentrate on the basic
aspects of the fittings.
Fittings
There are two basic types of fitting joints in hygienic
piping: welded and clamp. Welded fittings, unlike standard
buttweld pipe fittings, have an added tangent length to
accommodate the orbital welding machine. The orbital
welding machine allows the welding operator to make
consistent high quality autogenous welds. Autogenous welds
are welds made without filler metal. Fusion is made between
the parent metals of the two components being welded by
means of tungsten inert gas welding; more on welding in
Part II.
15
Figure 11 - Fittings Ready To Be Orbital Welded
Compliments of ARC Machines, Inc.
Figure 11 is an example of an orbital, or automatic,
welding machine mounted on its work-piece. In this example
it happens to be a 90° elbow being welded to a cross. You
can see by this example why the additional straight tangent
section of automatic weld fittings is needed. That extra
length provides a mounting surface for attaching the
automatic welding machine.
The clamp connection is a mechanical connection
whose design originated in the food and dairy industry, but
whose standardization has been under development by
ASME-BPE. Due to a lack of definitive standardization most
companies that use this type connection require in their
specifications that both the ferrule, the component that the
clamp fits on, and the clamp itself come from the same
manufacturer. This is to ensure a competent fit.
There are no specific dimensions and tolerances for the
clamp assembly, except for that which is being developed by
ASME-BPE. Currently it is possible to take a set of ferrules
from one manufacturer, mate them together with a gasket,
attach a clamp from a different manufacturer and tighten up
on the clamp nut. In some cases you can literally rotate the
clamp by hand about the ferrules. Meaning, there is no force
being applied on the joint seal.
For those of you unfamiliar with the clamp joint, it is
the clamp that applies the force that holds the ferrules
together. The fact that this can occur begs the need for
standardization to a greater degree than what currently
exists.
We‟ll get into this in greater detail in Part II, but another
issue that currently exists with the clamp joint is gasket
intrusion into the pipe ID due to inadequate compression
control of the gasket.
Gasket intrusion is a problem in pharmaceutical service
for two reasons: 1. Depending on the hygienic fluid service
and the gasket material the gasket protruding into the fluid
stream can break down and slough off into the fluid flow,
contaminating the hygienic fluid. 2. The intrusion of the
gasket into pipe ID on a horizontal line can also cause fluid
hold-up. This can result in the loss of residual product, cause
potential cross-contamination of product, and promote
microbial growth.
The reason I mention this here, and I won‟t go into it
any further until Part II, is because there are manufacturers
that are attempting to overcome these issues by improving
on the concept of the clamp joint.
Two manufactures, Swagelok and The Neumo
Ehrenberg Group, represented in the US by VNE, have,
what I would consider, well developed re-designs of the
standard hygienic clamp assembly.
Figure 12 – Swagelok TS Series Profile
Compliments Swagelok Company
Swagelok has developed what they call their TS series
fittings. These ferrules (Fig. 12) have a design that provides
compression control of the gasket while also controlling the
creep tendency inherent in, arguably, the most prevalent
gasket material used in high purity piping, Teflon.
Figure 13 – Maxpure Connect S
Compliments Neumo Ehrenberg Group
The Neumo Ehrenberg Group manufactures a clamp
joint (also provided as a bolted connection) that does not
require a gasket (Fig. 13). This type of joint, called the
Connect-S under their newly formed MaxPure label of
fittings, is currently in use in Europe. While this connection
alleviates the issues that are present with a gasketed joint
16
added care would need to be applied in its handling. Any
scratch or ding to the faced part of the sealing surface could
compromise its sealing integrity. Nevertheless this is a
connection design worth consideration.
In this first article we have covered a few of the basics,
which will provide us with a little more insight when we
discuss the more in-depth topics of piping Codes, piping
design, and fabrication of pipe in Part II.
Future Articles
What we have discussed so far is just some of the basics
of general piping. While there is a great deal left unsaid we
will provide further clarification as we move through the
next two articles.
The next article, titled “Piping Design Part II – Code,
Design and Fabrication”, will cover the more specific
aspects of Code governance, engineering in pipe design and
fabrication as it relates to welding, assembly and installation.
The third article in this series, titled “Piping Design Part
III – Installation, Cleaning, Testing and Verification”, will
wrap up the series by discussing the four title points.
Acknowledgement:
I wish to thank Earl Lamson, senior Project Manager with
Eli Lilly and Company, for taking time out of a busy
schedule to read through the draft of this article. He obliged
me by reviewing this article with the same skill, intelligence
and insight he brings to everything he does. His comments
kept me concise and on target.
About the author:
W. M. (Bill) Huitt has been
involved in industrial piping
design, engineering and
construction since 1965.
Positions have included
design engineer, piping design
instructor, project engineer,
project supervisor, piping
department supervisor,
engineering manager and
president of W. M. Huitt Co. a
piping consulting firm
founded in 1987. His
experience covers both the engineering and construction
fields and crosses industrial lines to include petroleum
refining, chemical, petrochemical, pharmaceutical, pulp &
paper, nuclear power, biofuel, and coal gasification. He has
written numerous specifications, guidelines, papers, and
magazine articles on the topic of pipe design and
engineering. Bill is a member of ISPE (International Society
of Pharmaceutical Engineers), CSI (Construction
Specifications Institute) and ASME (American Society of
Mechanical Engineers). He is a member of three ASME-
BPE subcommittees, several Task Groups, an API Task
Group, and sets on two corporate specification review
boards. He can be reached at:
W. M. Huitt Co.
P O Box 31154
St. Louis, MO 63131-0154
(314)966-8919
www.wmhuitt.com
As published in the June and July 2007 issues of Chemical Engineering Magazine
There is not a reason sufficiently good enough not to comply with appropriate industry Standards and
Codes. W. M. (Bill) Huitt
W. M. Huitt Co.
A request was put to me a few years back asking if I
would respond in writing to the question, “Why do we, as a
company, need to comply with a piping Code?” The
question was in regard to the building of industrial facilities,
and was in preparation for a meeting that was about to take
place for which the main topic was going to be the issue of
Code compliance.
If you considered the question while reading it you may
have noticed that there is, although unintentional, a trick to
it. Code, by definition is law with statutory force. Therefore
the reason for complying with a Code is because you
literally have to, or be penalized for non-compliance.
The question actually intended was, “why comply with
or adopt a piping consensus standard?” When a question like
the one above is phrased as it is it supports my contention
that many people, referring to engineers and designers in our
case, do not fully understand the difference between a Code
and a Standard. And it doesn‟t help matters when some
Standards are published as a Code, and some Codes are
published as a Standard. This is certainly nothing to get
excited about, but it is something worth pointing out.
My take on the reason for the misunderstanding of these
two closely related terms, Standard and Code, is that they
get bounced around so often in the same context that
designers and engineers simply begin interchanging the two
terms without much consideration for their different
meanings. I‟m going to explain the difference between a
Standard and a Code, but before I do, here‟s the written
response I gave to the above question:
Consensus Standards such as those published by ASME,
ANSI, API, NFPA, ASTM, International Plumbing Code and
others are not mandatory in and of themselves. However,
federal, state, city and other local Codes are mandatory. In
these municipal Codes you will find regulations that
establish various requirements taken in whole, or in part
from the Standards published by the above listed
organizations, and others, as legally binding requirements.
These Standards, as adopted, then become Code, which is
enforceable by law.
When not addressed on a municipal level, but included
in corporate specifications, the Standard becomes a legal
Code on a contractual basis.
To comply with these Codes, irrespective of government
regulations or corporate requirements, doesn't cost the
builder any more than if they didn't comply. It does,
however, cost more to fabricate and install piping systems
that have a high degree of integrity as opposed to a system
that doesn't.
By hiring non-certified welders and plumbers, by-
passing inspections, examinations and testing, using
material that may potentially not withstand service pressures
and temperatures, and supporting this type of system with
potentially inadequate supports is less costly but there's too
much at risk. I don't think anyone in good conscience would
Piping Design
Part 2: Code, Design and
Fabrication
2
intentionally attempt to do something like that in order to
save money, but then again the world is full of unscrupulous
individuals and corporations.
If anyone intending on fabricating and installing a
piping system plans to:
1. Use listed material,
2. Specify material that meets the requirements for fluid
service, pressure and temperature,
3. Inspect the material for MOC, size and rating,
4. Use certified welders and plumbers,
5. Inspect welds and brazing,
6. Adequately support the pipe,
7. Test the pipe for tightness;
Then they are essentially complying with Code. The Code
simply explains how to do this in a formal, well thought-out
manner.
There is not a reason sufficiently good enough not to
comply with appropriate industry Standards and Codes. If
there was a fee involved for compliance this might be a
stimulus for debate. But there is no fee, and there is usually
just too much at stake. Even with utility systems in an admin
building or an institutional facility, the potential damage
from a ruptured pipeline, or a slow leak at an untested joint
could easily overshadow any savings gained in non-
compliance. That's without considering the safety risk to
personnel.
The first thing that someone should do, if they are
considering to do otherwise, is check local and state Code.
They may find regulations that require adherence to ASME,
the International Plumbing Code or some of the other
consensus Standards. If not already included, this should be
a requirement within any company’s specifications.
Just a bit of trivia:
ASME published the first edition of the Boiler and
Pressure Vessel Code in 1914-15. Prior to creation of the
Code, and what played a large part in instigating its
creation, was that between 1870 and 1910 approximately
14,000 boilers had exploded. Some were devastating to both
people and property. Those numbers fell off drastically as
the Code was adopted.
Uniformity and regulation does have its place.
PIPING CODE
In a piping facility, defined here as an industrial facility
requiring a significant amount (apply your own order of
magnitude here) of pipe, the three key factors in its
development are the governing Code, the design (includes
specifications and engineering), and pipe fabrication
(includes installation). These are the three topics we will
discuss on a broad, but limited basis in this article.
Like the seatbelt law Code compliance is not just the
law, it makes good sense. A professional Consensus
Standard is, very simply put, a Code waiting to be adopted.
Take the ASME Boiler and Pressure Vessel Code (BPVC),
since its first publication in 1915 it has been adopted by 49
states, all the provinces of Canada, and accepted by
regulatory authorities in over 80 countries.
On May 18, 2005 it was finally adopted by the 50th
state, South Carolina. And this doesn‟t mean the BPVC is
adopted in its entirety. A state, or corporation for that matter,
can adopt a single section or multiple Sections of the BPVC,
or they can adopt it in its entirety. Until South Carolina
adopted the BPVC it was actually no more than a Standard
in that state and only required compliance when stipulated in
a specification. However, in all honesty you would not get a
US boiler or pressure vessel manufacturer to by-pass Code
compliance. That is, unless you wanted to pay their potential
attorneys fees.
With regard to Code compliance, the question I get
quite often is, “How do I determine which piping Code, or
Standard, I should comply with for my particular project?”
Determining proper Code application is relatively
straightforward while at the same time providing a certain
degree of latitude to the Owner in making the final
determination. In some cases that determination is made for
the Engineer or Contractor at the state level, the local level
or by an Owner company itself. Providing guidelines for
Code adoption on a project basis is direction that should be
included in any company‟s set of specifications, but quite
often is not. This can cause a number of disconnects through
design and construction.
In order to answer the question about Code assignment
some history has to be told. In keeping this brief I will just
touch on the high points. In 1942, ASA B31.1 – American
Standard Code for Pressure Piping was published by the
American Standards Association. This would later change to
B31.1 - Power Piping. In the early 1950‟s the decision was
made to create additional B31 Codes in order to better define
the requirements for more specific needs. The first of those
Standards was ASA B31.8 – Gas Transmission and
Distribution Piping Systems, which was published in 1955.
In 1959 the first ASA B31.3 – Petroleum Refinery Piping
Standard was published.
After some reorganization and organizational name
changes the ASA became ANSI, American National
Standards Institute. Subsequent Code revisions were
designated as ANSI Codes. In 1978, ASME was granted
accreditation by ANSI to organize the B31 Committee as the
ASME Code for Pressure Piping. This changed the Code
designation to ANSI/ASME B31.
3
Since 1955 the B31 Committee has continued to
categorize, create and better define Code requirements for
specific segments of the industry. Through the years since
then they have created, not necessarily in this order, B31.4 –
Liquid Transportation Piping, B31.5 – Refrigeration Piping,
B31.9 – Building Services Piping, and B31.11 – Slurry
Transportation Piping. Each of these Standards is considered
a stand-alone Section of the ASME Code for Pressure
Piping, B31.
What the B31 committee has accomplished, and is
continuing to improve upon, are Standards that are better
focused on specific segments of industry. This alleviates the
need for a designer or constructor building an institutional
type facility from having to familiarize themselves with the
more voluminous B31.3 or even a B31.1. They can work
within the much less stringent and extensive requirements of
B31.9, a Standard created for and much more suitable for
that type of design and construction.
As mentioned above, ASME B31.1 – Power Piping, was
first published in 1942. Its general scope reads: “Rules for
this Code Section have been developed considering the
needs for applications which include piping typically found
in electric power generating stations, in industrial and
institutional plants, geothermal heating systems, and central
and district heating and cooling systems.”
The general scope of ASME B31.3 – Process Piping,
reads: “Rules for the Process Piping Code have been
developed considering piping typically found in petroleum
refineries, chemical, pharmaceutical, textile, paper,
semiconductor and cryogenic plants; and related processing
plants and terminals.”
ASME B31.5 – Refrigeration Piping, applies to
refrigerant and secondary coolant piping systems.
Closely related to B31.1, but not having the size,
pressure or temperature range, B31.9 was first published in
1982. It was created to fill the need for piping in limited
service requirements. Its scope is narrowly focused on only
those service conditions that may be required to service the
utility needs of operating a commercial, institutional or
residential building.
From its shear scope of responsibility, B31.3
encompasses virtually all piping, including those also
covered by B31.1 (except for boiler external piping), B31.5
and B31.9. The difference, and distinction, as to which Code
should apply to a particular project, lies with the definition
and scope of the project itself.
If a project includes only the installation of perhaps a
refrigeration system, B31.5 would apply. If a project's scope
of work consists of an office, laboratory, research facility,
institutional facility or any combination thereof, B31.1 or
B31.9 and possibly B31.5 would apply. A laboratory or
research facility could possibly require fluid services beyond
the fluid service limits of B31.9. In that case, B31.3 would
be adopted for those services.
In the case of a process manufacturing facility, B31.3
would be the governing Code. Since B31.3 covers all piping,
B31.5 or B31.9 would not need to be included, not even
necessarily with associated lab, office and research facilities.
The only time B31.5 or B31.9 would become governing
Codes, in association with a manufacturing facility, is if a
refrigeration unit, or an office, lab and/or research facility
were under a separate design/construct contract from the
process manufacturing facility. Or they were a substantial
part of the overall project.
As an example, project XYZ consists of a process
manufacturing facility, related office building and lab
facilities. If the utility service piping for the office and lab
facilities is a small percentage of the overall project, and/or
the design and construction contracts for those facilities are a
part of the overall process manufacturing facility, all piping,
with Code exclusions, could be governed by B31.3.
If, however, the office and lab facilities were a
substantial part of the overall project, or they were to go to a
separate constructor it may be more beneficial to determine
battery limits for those facilities and designate anything
inside those battery limits as B31.1 or B31.9 and/or B31.5.
In such a case, separate pipe specifications may have to be
issued for those portions of the project designated as being
governed by B31.9. This is due to the range of fluid services
and the corresponding pressure and temperature limits of
B31.9 compared to those of B31.3. These differences in
Code assignment and battery limits may be a driver for the
project‟s contracting strategy.
Many piping service requirements such as steam, air,
chilled water, etc. can come under the auspices of multiple
Codes. These fluid services, which fall within the definition
of B31.3 Category D fluid services, can just as easily fall
within the requirements of B31.1 or B31.9 as well. In an
effort at maintaining a high degree of continuity in the
process of making the determination of which Code to apply
to a project, company guidelines should be well defined.
The final determination as to what constitutes a
governing Code, within the purview of the above mentioned
Codes, is left to the Owner and/or to the local governing
jurisdiction. Engineering specs should clarify and reflect the
intent of the Owner and the respective Codes in an attempt
to provide consistency and direction across all projects
within a company.
PIPING DESIGN
Piping design is the job of configuring the physical
aspects of pipe and components in an effort to conform with
P&ID‟s, fluid service requirements, associated material
4
specifications, equipment data sheets, and current Good
Manufacturing Practice while meeting Owner expectations.
All of this has to be done within a pre-determined three-
dimensional assigned space while coordinating that activity
with that of the architecture, structural steel, HVAC,
electrical, video, data & security conduit and trays, and
operational requirements.
Pulling together and coordinating the above mentioned
discipline activities to achieve such a compilation of design
requires a systematic methodology, planning, technical
ability, coordination, foresight, and above all experience.
A note of omission here: CAD (Computer Aided Design)
is such an integral part of piping design that it’s difficult, if
not impossible, to discuss design without including CAD in
the discussion. It plays such a large part that, rather than
enter into it here, I will dedicate an entire article to it at a
later date. That article will discuss the integration of CAD
into the industry including its merits, and how, in many
respects, its method of implementation and integration has
inversely diminished the quality of design with respect to
industrial piping. The article will also discuss industry’s
reaction to this unexpected result, and the issues we are still
dealing with today in the use of CAD.
PIPING SPECIFICATIONS
One of the first activities the piping engineer will be
involved with is development of piping specifications,
design guidelines and construction guidelines. Piping
specifications, as an overview, should provide essential
material detail for design, procurement and fabrication.
Guidelines, both design and construction, should provide
sufficient definition in a well organized manner to allow the
designer and constructor the insight and direction they need
in order to provide a facility that will meet the expectation of
the Owner with minimal in-process direction from the
Owner or Construction Manager.
Piping Specifications
A Piping Specification is the document that will
describe the physical characteristics and specific material
attributes of pipe, fittings and manual valves necessary to the
needs of both design and procurement. These documents
also become contractual to the project and those contractors
that work under them.
Design will require a sufficient degree of information in
a specification that will allow for determining the service
limitations of the specification and what fluid services the
specification‟s material is compatible with. That is, a project
may have, among other fluid services, sulfuric acid and
chilled water. The economic and technical feasibility of the
material selection for chilled water service would not be
technically feasible for sulfuric acid. Inversely, the economic
and technical material selection for sulfuric acid service
would not be economically feasible for chilled water service.
Procurement too, will need detailed specifications to
limit the assumptions they will have to make or the
questions they will have to ask in preparing purchase orders.
The piping specification should make clear exactly what the
material of construction is for each component, and what
standard that component is manufactured to. Also included
in the component description should be pressure rating, end
connection type and surface finish where required.
There are a few rather consistent mistakes that
companies make in developing or maintaining specs: 1.
within the spec itself they are either not definitive enough or
they are too definitive; 2. they are not updated in a timely
manner; and/or 3. The specs are too broad in their content.
In defining the above issues we‟ll begin with:
Point #1: When defining pipe and components in a
specification you should provide enough information to
identify each component without hamstringing yourself or
procurement in the process. What I mean by that is, do not
get so specific or proprietary with the specification that only
one manufacturer is qualified to provide the component,
unless you intend to do just that. With standard pipe and
fittings it‟s difficult to provide too much information.
However, with valves and other inline equipment it can
happen quite easily.
A common practice of spec writers is to write a
specification for a generic type valve, one that can be bid on
by multiple potential suppliers, by using the description of
one particular valve as a template. What happens is that
proprietary manufacturer trade names, such as some of the
trim materials, are carried over to the generic valve spec.
When the procurement person for the mechanical contractor,
or whoever is buying the valves for the project, gets ready to
buy this valve the only manufacturer that can supply it with
the specified proprietary trim is the one from which the spec
was copied.
You would think that, in doing this, it would eliminate
multiple bids for the valve based on the unintentional
proprietary requirements in the spec. In actuality it creates
confusion and propagates questions. The valve bidders, other
than the one the spec was based on, will bid the valve with
an exception to the proprietary material, or they will contact
the purchasing agent for clarification. Since the purchasing
agent won‟t have the answer, the question, or actually the
clarification, then goes back to the engineer and/or the
Owner. The time necessary in responding to these types of
issues is better spent on more pressing matters.
When developing a spec be specific, but try not to
include proprietary data unless you intend to. As an example
when specifying Viton you are specifying a generic DuPont
5
product. Generic in that there are several different types of
Viton such as Viton A, Viton B, Viton GF, Viton GFLT, etc.
Each of these has specific formulations, which gives them
different fluid service compatibility and pressure/
temperature ranges. Viton is a type of fluorocarbon.
Fluorocarbons are designated FKM under ASTM D-1418.
So when specifying “Viton” you are identifying a specific
product from a specific manufacturer…almost.
If, in developing a specification, you wish to establish
minimum requirements for a component or a material it is
certainly acceptable to identify a specific proprietary item as
a benchmark. In doing this, and we‟ll stay with the
fluorocarbon gasket or seal material example, you could
identify Viton GF or equal, which would indicate that a
comparable material from one of the other fluorocarbon
manufacturers would be acceptable so long as the fluid
service compatibility and pressure/temperature ranges were
equal to or greater than the Viton GF material.
In saying “almost” above what I meant by that is, if you
write the spec as Viton you would most likely get the
original formulation, which is Viton A. The fluid service
may be more suited for an FKM with
polytetrafluoroethylene in it. That would be a Viton GF. Or
an FKM suitable for colder temperatures may be a better
choice. That would be a Viton GFLT. Be specific for those
that have to use the specs to design from and those that have
to purchase the material.
Point #2: All too often after a specification is developed
it will reside in the company‟s database without being
periodically reviewed and updated. Industry standards
change, part numbers change, manufacturers are bought and
sold; manufacturers improve their products, etc. All of these
things constitute the need and necessity to review and revise
specifications on a timely basis.
A company that houses their own set of specifications
should review those specifications at least every two years.
This timing works out for a couple reasons: 1. industry
standards, on average, publish every two years, and 2.
capital projects, from design through close-out, will arguably
have an average duration of two years. Lessons-learned from
projects can then be considered for adoption into company
specs, prompting a new revision.
Point #3: Specs being too broad in their content refers to
an attempt at making the specs all-inclusive. A piping
specification should contain only those components and
information that would typically be used from job to job.
That would include the following (as an example):
1. Pressure/Temperature limit of the spec
2. Limiting factor for Pressure/Temperature
3. Pipe material
4. Fitting type, rating and material
5. Flange type, rating and material
6. Gasket type, rating and material
7. Bolt & nut type and material
8. Manual valves grouped by type
9. Notes
10. Branch chart matrix with corrosion allowance
The ten line items above provide the primary
component information and notations required for a typical
piping system. Some specifications are written to include
such components as steam traps, sight glasses, 3-way or 4-
way valves, strainers, and other miscellaneous type items.
Those miscellaneous items are better referred to as specialty
items (or some other similar descriptive name) and are sized
and specified for each particular application. This does not
make them a good candidate for inclusion into a basic pipe
specification.
To explain the above we can use, as an example, a
carbon steel piping system that is specified to be used in a
150 psig steam service. The pipe, flanges, fittings, bolts,
gaskets and valves can all be used at any point in the system
as specified. The specification for a steam trap, however,
will vary depending on its intended application. And
depending on its application the load requirements for each
trap may vary.
As an example, a steam trap application at a drip leg
will have a light steady load, whereas a steam trap
application at a shell & tube heat exchanger may have a
heavier modulating load. And that doesn‟t take into account
the need for the different types of traps, e.g. F&T, inverted
bucket, thermodynamic, etc.
You could, depending on the size of the project, have
multiple variations of the four basic types of steam traps
with anywhere from 30 to 300 or more traps in multiple
sizes and various load requirements. I think you can see why
this type of requirement needs to be its own specification
and not a part of the piping specification.
A piping specification should be concise, definitive and
repeatable. Adding specialty type items to the specification
makes it convoluted and difficult to control and interpret.
Users of these specifications are designers, bidders,
procurement personnel, fabricators, receipt verification
clerks, validation and maintenance personnel.
With that in mind you can better understand, or at least
value the fact, that these documents have to be interpreted
and used by a wide range of personnel. Those personnel are
looking for particular information, written in a concise
manner that will allow them to design and order or verify
components within that specification. In attempting to
include the specialty type items it will, at the very least,
complicate and exacerbate the process.
DESIGN AND CONSTRUCTION GUIDELINES
6
Design and construction guidelines, working in
conjunction with the piping specifications, should convey to
the designer and constructor point by point requirements as
to how a facility is to be designed and constructed. The
guidelines should not be a rhetorical essay, but instead
should follow an industry standard format, preferably a CSI
(Construction Specifications Institute) format.
Look at it this way, the material specifications tell the
designer and constructor what material to use; the guidelines
should tell them how to assimilate and use the material
specifications in applying them to Good Design Practice.
Without these guidelines as part of any bid package or
Request For Proposal package, the Owner is essentially
leaving it up to the Engineer and/or Constructor to bring
their own set of guidelines to the table. And this may or may
not be a good thing. Leaving the full facilities delivery to the
Engineer and Constructor depends a great deal on the
qualifications of the Engineer and the Constructor, and
whether or not consistency from plant to plant and project to
project is an issue.
If the Owner approaches a project with expectations as
to how they would like their plant or facility designed and
built then some preparation, on the Owner‟s part, is in order.
Preparation should include, not only material specifications
as described earlier, but also the guidelines and narratives
(yes, narratives) necessary to define the design and
construction requirements.
I mention the use of narratives here because it helps
facilitate the understanding and convey the magnitude of the,
in most cases, reams of specifications and guidelines
necessary to build an industrial facility of any appreciable
size.
A narrative, in general, should explain in simple,
straight-forward language, for each discipline, the
numbering scheme used for the specifications and
guidelines; association between the material specifications
and the guidelines; an explanation as to why the project is
governed by a particular Code or Codes; and a brief
description of expectation.
The narrative allows you to be more explanatory and
descriptive than a formal point-by-point specification. It
gives the bidder/Engineer a Readers Digest version of the
stacks of specifications and guidelines they are expected to
read through and assimilate within a matter of a few weeks
How piping specifications are delivered to a project can
have a significant impact on the project itself. There are,
generally speaking, three scenarios in which project
specifications and guidelines are delivered to a project:
1. In scenario 1 the Owner, or Customer, has
developed, throughout their existence, a
complete arsenal of specifications and
guidelines. In the older, more established
petroleum refining and chemical companies you
will see entire departments whose mission is to
create, maintain and refine all of the
specifications and guidelines necessary to
execute a project. When a project is approved to
go out for bid to an Engineer the necessary
specifications and guidelines, along with the
requisite drawings, are assembled, packaged and
provided to the Engineer as bid documents, and
beyond that as working documents in the design,
engineering and construction efforts.
2. In scenario 2 the Owner, or Customer, has some
specifications and guidelines that have possibly
not been updated for several years. These are
provided to the Engineer with the understanding
and stipulation that any errors or omissions in
the documents should be addressed and
corrected by the Engineer. These too would be
used in the bid process as well as on the project
itself.
3. In scenario 3 the Owner, or Customer, brings no
specifications or guidelines to the project table.
Specification development becomes part of the
overall project engineering effort.
Scenarios 1 and 3 are at opposite ends of the spectrum,
but afford the best situation for both the Owner and
Engineer/Constructor. By providing the Engineer and
Constructor, as in scenario 1, with a full set of current
specifications and well articulated guidelines, making the
assumption that both the engineer and constructor are
qualified for the level of work required, they can very
effectively execute the design, engineering and construction
for the project.
Scenario 3 allows the Engineer and Constructor to bring
their own game-plan to the project. This too is effective, due
only to the fact that the learning curve is minimal. Most
engineering firms will be prepared to execute a project with
their own set of specifications and guidelines. This applies to
qualified Constructors as well. The down-side of this is the
project to project inconsistency in specifications and
methodology when using different engineers and
constructors.
Scenario 2 is a worse case situation. Ineffective and
outdated Owner specifications create confusion and
inefficient iterations in both the bid process and the
execution of a project. It additionally creates the greatest
opportunity for conflicts between Owner documents and the
Engineer‟s documents. For Project Management, this
translates into change orders at some point in a project.
A guideline should explain to the engineering firm or
constructor, in a concise, definitive manner, just what it is
the Owner expects of them in executing the design and
construction of a facility. By actively and methodically
developing a set of guidelines an Owner/Customer does not
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have to rely on an outside resource, such as an engineering
firm or constructor, to hopefully provide them with the
facility they require and hope to get.
Developing guidelines to convey your company‟s
requirements and expectations can be accomplished using
one or both of the following two basic methods:
1. A formal point-by-point format that covers
all necessary criteria that you, as the Owner,
require on a proprietary basis, plus a listing
and description of the necessary Code and
cGMP requirements.
2. A narrative, for each discipline, that allows
the writer to expand and define, in a much
more descriptive manner, the points that
aren‟t made clear enough, or readily
apparent in the more formal format.
The guideline itself can be structured based on one of
the CSI formats. The format examples provided by CSI give
a company sufficient flexibility in writing guidelines, or
specifications for that matter, to allow the document to
conform to their own particular brand of requirements and
nuances. It also lends a degree of intra-industry conformity
to the guidelines and specifications, providing a degree of
familiarity to the engineers and constructors that will have to
adhere to them.
Design Elements
In the first paragraph of this segment of the article,
“Piping Design”, I described the act of designing piping
systems for a facility as bringing a number of technical
components together to make the pipe conform to a specific
set of requirements, within a prescribed area.
That‟s pretty simplistic, and does not really convey the
magnitude of the experience, technical background or the
imagination required to execute such a task. Experience is
the essential component here. And that is simply because,
aside from whatever innate ability a good designer might
possess, the knowledge required is not taught through formal
education, but is instead learned by being involved in the
process of hands-on design over a period of time
accompanied by ongoing learning.
Ongoing learning can be in the form of organized
classes, a mentor and/or any other means available to help
learn and understand the physical requirements and restraints
of the various systems you will be designing and industries
you will be serving.
Since we do not have enough space here to cover all of
the design elements I would like to, I will key in on a few
topics that generally find their way to me for clarification.
And this doesn‟t even scratch the surface. We will discuss
flanges, pipe internal surface finish, weld seam factor, pipe
wall thickness, MAWP/MADP, design pressure/temperature,
and charge accumulation.
Flanges
In the learning process, some designers (I include
engineers as well) will gloss over some of the primary basics
of design and go directly to the bottom line information they
need. Case in point: In Part I, of this series of articles, we
discussed ASME flanges and their Classifications. Most
designers are familiar with ASME flange Classifications
such as 150, 300, 400, etc. And even though verbally stating
150 pound flange (we discussed the origin of this term in
Part I) rolls off the tongue much easier and is still an
industry accepted term; Class 150 is the proper terminology
and designation.
What you may not know is that the Class designation is
a factor in the calculation for determining the rated working
pressure of a flange. That calculation is:
(eq. 1)
Where:
Pc = ceiling pressure, psig, as specified in
ASME B16.5, para. D3 at temperature T
PT = Rated working pressure, psig,for the
specified material at temperature T
Pr = Pressure rating class index, psi1 (e.g., Pr =
300 psi for Class 300)
S1 = Selected stress, psi, for the specified
material at temperature T. See ASME
B16.5, paras. D2.2, D2.3 and D2.4. 1 This definition of Pr does not apply to Class 150. See ASME
B16.5, paras. D2.2, D2.3 and D2.4.
Pipe Internal Surface Finish
Internal surface roughness is a topic that is specific to
the pharmaceutical, bio-pharmaceutical and semiconductor
industries, but can also be an issue in the chemical industry.
Quantifying and specifying a maximum surface
roughness for internal pipe wall for use in, what is referred
to as direct impact fluid services, is a necessity in the above
mentioned industries.
Direct impact piping systems are those systems that
carry product or carry a fluid service that ultimately comes
in contact with product.
The need for a relatively smooth internal pipe wall is
predicated on three primary issues as it relates to the
industries mentioned above. Those issues are: 1.
Cleanability/Drainability, 2. The ability to hinder the growth
(we don‟t yet have the ability to control it) of biofilm and to
enhance the ability to remove it once it does appear, and 3.
To reduce, to a microscopic level, crevices in which
8
)(2 PYSE
PDt
microscopic particles can reside and at some point dislodge
and get carried along in the fluid stream to damage product.
Regarding the first point, cleanability and drainability
are associative in this context. Meaning that, in order for a
system to be fully cleanable it has to be designed and laid
out in a manner that will eliminate any pockets and provide
enough slope to eliminate any residual liquid (drainable).
Not only is this residual liquid, or hold-up, a contaminant,
from both a bacterial standpoint and as a cross batch
contaminant, it can also be costly due to the high cost of
some drug products. Along those lines, the ASME-BPE
Standard provides criteria for minimum slope, maximum
deadleg, gasket intrusion, gasket concavity, and many other
criteria for design of cleanable and drainable hygienic piping
systems.
Regarding the second point, biofilm (Fig. 1) is defined
as a bacterial population composed of cells which are firmly
attached as microcolonies to a solid surface.
A paper titled, “Microbial Biofilms – are they a problem
in the Pharmaceutical Industry?”, was delivered at an
ASME-BPE symposium in Cork, Ireland, June 2004 by
Frank Riedewald, a Senior Process Engineer with
Lockwood-Greene IDC Ltd. In it he explains the results of
testing that was performed to determine the relative
association between the formation of biofilm, pipe wall
surface finish and pipe wall surface cleanability.
Fig. 1 – Biofilm magnified ≈2000X
(Courtesy of Mr. Riedewald)
One of the many interesting factors that came from the
studies mentioned in this paper is the fact that the internal
surface of the pipe wall can actually be too smooth.
Referring to the graph in Fig. 2, results of the studies in the
above mentioned paper indicate that the surface finish range
best suited to reduce biofilm adherence to the internal pipe
wall surface is from 0.4Ra µm to 1.Ra µm (15.7Ra µin to
58.8Ra µin). What this implies is that while we currently do
not have the means to prevent the onset of biofilm on the
internal walls of hygienic or semiconductor piping systems
we can facilitate its removal in the cleaning process by
specifying the proper surface finish of the internal pipe
walls.
The accepted max surface finish in the pharmaceutical
and bio-pharmaceutical industries is 25Ra µin (0.6 µm). In
the semiconductor industry you might typically see surface
finishes in the 7Ra µin to 15Ra µin, particularly in gas
delivery systems. While the pharmaceutical industry is
concerned with bacterial growth and cross contamination,
the semiconductor industry is concerned more with
particulate damage to product, on the microscopic level.
This pertains to point three above.
Fig. 2 – Biofilm Attachment vs Surface Roughness
(Courtesy of Mr. Riedewald)
Pipe Weld Seam Factor
Part I, of this series of articles, mentioned the fact that
the weld seam in longitudinally welded pipe is a factor in the
pipe wall pressure design thickness calculation.
In ASME B31.3 there are two pipe wall thicknesses to
calculate for. One is pressure design thickness (t) and the
other is minimum required thickness (tm).
There are two equations for finding pressure design
thickness (t) for straight pipe under internal pressure. One is
where t < D/6. This calculation (eq. 2) is based on internal
pressure, actual (not nominal) OD of the pipe, stress value of
the material at design temperature, joint efficiency factor,
and the coefficient Y [a factor used to adjust internal
pressure (P) for a nominal material at temperature].
The other calculation used is that in which t ≥ D/6. This
calculation (eq. 3) is based on the above listed criteria except
for the OD and uses instead ID of the pipe, and the sum of
all mechanical allowances.
The two equations look like this:
Where t < D/6:
(eq. 2)
Where t ≥ D/6:
9
)]1([2
)2(
YPSE
cdPt
cttm
(eq. 3)
Where:
t = Pressure design thickness
tm = Minimum required thickness, including
mechanical, corrosion, and erosion
allowances
c = Sum of the mechanical allowances (thread
or groove depth) plus corrosion and
erosion allowances. For threaded
components, the nominal thread depth
(dimension h of ASME B1.20.1, or
equivalent) shall apply. For machined
surfaces or grooves where the tolerance is
not specified, the tolerance shall be
assumed to be 0.02 in. (0.5 mm) in
addition to the specified depth of the cut.
D = Actual pipe OD
d = Pipe ID
P = Internal design gage pressure
S = Stress value for material from ASME
B31.3 Table A-1, at design temperature
E = Quality factor, or joint efficiency factor
Y = Coefficient from ASME B31.3 Table
304.1.1, valid for t < D/6.
The minimum required thickness (tm) is simple enough:
(eq. 4)
To determine wall thickness for pipe under external
pressure conditions refer to the Boiler and Pressure Vessel
Code (BPVC) Section VIII, Division 1, UG-28 through UG-
30 and ASME B31.3, Para. 304.1.3.
Keep in mind that for seamless pipe E will be removed
from equations eq. 2 & eq. 3.
Taking a page from the BPVC we will go through a few
brief steps to determine Maximum Allowable Working
Pressure (MAWP) for straight pipe. But let me begin by
saying that MAWP is not a B31.3 expression, it comes from
the BPVC. We will instead transpose this term to MADP
(Maximum Allowable Design Pressure), which is also not a
B31.3 term, but more closely relates to piping.
When a vessel goes into design it is assigned a
coincidental design pressure and temperature. These are the
maximum conditions the vessel is expected to experience
while in service, and what the vessel engineers will design
to. The material, material thickness, welds, nozzles, flanges,
etc. are all designed predicated on this predetermined design
criteria.
Throughout design the vessel‟s intended maximum
pressure is referred to as its design pressure. All calculations
are based on specified material and component tolerances
along with fabrication specifics, meaning types and sizes of
welds, reinforcement, etc. Not until after the vessel is
fabricated can the engineer know what the actual material
thickness is, the type and size of each weld, thickness of
each nozzle neck, etc. Only when all of the factual data of
construction is accumulated and entered into vessel
engineering programs can the MAWP be determined. This
value, once determined, then replaces the design pressure,
and is calculated based on the installed configuration of the
vessel. That is, mounted vertically or horizontally; mounted
on legs; or mounted on lugs.
The difference between the design pressure and the
MAWP is that the engineer will design to the design
pressure, but the final MAWP is the limiting pressure of the
vessel, which may exceed the design pressure; it can never
be less than the design pressure.
In applying this to piping we will first calculate the
burst pressure of the pipe and then determine the MAWP, or,
as was mentioned earlier, a term more closely related to
piping, the Maximum Allowable Design Pressure (MADP).
There are three equations generally used in calculating
burst pressure for pipe. They are:
The Barlow formula;
(eq. 5)
The Boardman formula:
(eq. 6)
The Lame` formula:
(eq. 7)
Where:
PBA = Burst Pressure, psig (Barlow Formula)
PBO = Burst Pressure, psig (Boardman Formula)
PL = Burst Pressure, psig (Lame` Formula)
D = Actual pipe OD, inches
d = Pipe ID, inches
TF = Wall thickness, inches, minus factory
tolerance
ST = Minimum tensile strength, psi, from
D
STP TF
BA
2
)8.0(
2
TD
STP TF
BO
)(
)(22
22
dD
dDSP T
L
)8.0(
2
TD
STP TF
BO
10
B31.3 Table A-1
Sf = Safety factor, a factor of 3 or 4 is applied
to burst pressure to determine MADP
M = Maximum Allowable Design Pressure
(MADP)
Using the results from any one of the above equations
we can then solve for MADP as follows:
(eq. 8)
** = BA, BO, or L subscript
Design Pressure and Temperature
The ASME B31.3 definition for Design Pressure and
Design Temperature is stated as two separate definitions. I
will integrate them into one by stating: The design pressure
and temperature of each component in a piping system shall
be not less than the most severe condition of coincident
internal or external pressure and temperature (minimum or
maximum) expected during service.
It goes on to state: The most severe condition is that
which results in the greatest required component thickness
and the highest component rating.
How do you determine these values and where do you
apply them? We‟ll cover the where first. What we did earlier
in determining pipe wall thickness was based on design
conditions, in which P = Internal Design Gage pressure and
S = Stress value at design temperature. Design conditions are
also used to determine component rating and as a basis for
determining leak test pressure, which we will get into in the
final article of this series.
There is no published standard, or real industry
consensus on how to determine design conditions. It
basically comes down to an Owner‟s or engineer‟s
experience. What I will provide here is a resultant
philosophy developed from many sources along with my
own experiences.
In understanding what constitutes design conditions we
first of all need to define them. Following is some accepted
terminology and their definitions:
System Operating Pressure: The pressure at which a
fluid service is expected to normally operate at.
System Design Pressure: Unless extenuating process
conditions dictate otherwise, the design pressure is the
pressure at the most severe coincident of internal or external
pressure and temperature (minimum or maximum) expected
during service, plus the greater of 30 psi or 10%.
System Operating Temperature: The temperature at
which a fluid service is expected to normally operate at.
System Design Temperature: Unless extenuating
process conditions dictate otherwise, the design
temperature, for operating temperatures between 32°F and
750°F, shall be equal to the maximum anticipated operating
temperature, plus 25°F rounded off to the next higher 5°.
Applying a sort of philosophy created by the above
definitions is somewhat straight forward for utility services
such as steam, water, non-reactive chemicals, etc. However,
that part of the above definitions for design conditions that
provide the caveat, “…extenuating process conditions…”
implies a slightly different set of rules for process systems.
Extenuating process conditions can mean increased
pressure and temperature, beyond that defined above, due to
chemical reaction, loss of temperature control in heat
transfer, etc.
Charge Accumulation of Lined Pipe
Clarification
Internal and external charge accumulation, known as
static electricity, or more technically known, as triboelectric
charge accumulation, is the result of charge generation
unable to dissipate. If a charge generated in a flowing fluid
is allowed to dissipate to ground, as it does in grounded
metallic pipe, then there is no problem. However, if a charge
cannot dissipate and is allowed to accumulate, it now
becomes a problem by potentially becoming strong enough
to create an Electrostatic Discharge (ESD). With regard to
thermoplastic lined pipe there are two forms of this to be
considered: External Charge Accumulation (ECA) and
Internal Charge Accumulation (ICA).
External Charge Accumulation
ECA is a concern with lined pipe due to the possibility
of not achieving spool-to-spool continuity during installation
due, in large part, to improved paint primer on flanges.
To explain the loss of spool-to-spool continuity: this
lack of integral continuity is, as mentioned above, the result
of the prime paint coat that is applied by the manufacture.
When pipe spools, lined or un-lined, are joined by flanges
using non-metallic gaskets the only thing that completes the
Spool-to-spool continuity is the bolting. The improved paint
primer on lined pipe flanges makes this more difficult to
achieve because normal bolt tightening doesn‟t guarantee
metal-to-metal contact between the nut and the flange.
Pipe generally does not come with a prime coat of paint,
however lined pipe does. Since flange bolts are used to
complete continuity from spool to spool the installer has to
make certain, when installing lined pipe, that the bolts, at
least one of the bolts, has penetrated the primer and made
contact with bare metal. This was achieved in the past by
fS
PM **
11
using star washers on at least one flange bolt while assuming
possible bare metal contact with the other bolts allowing the
washers, as they were tightened, to scrape away the prime
coat so that contact was made with the bare metal of the
flange. With improved prime coat material this is no longer a
guarantee.
If continuity from spool to spool is not achieved any
charge generation resulting from an internal or an external
source cannot readily dissipate to ground. The voltage in
triboelectric charge generation will build until it is strong
enough to jump to the closest grounded object creating an
undesired spark of electricity in doing this (Electrostatic
Discharge).
Internal Charge Accumulation
ICA, with regard to pipe, is unique to thermoplastic
lined pipe and solid thermoplastic pipe. Without being
impregnated with a conductive material, thermoplastics are
not good conductors of electricity. PTFE
(Polytetrafluoroethylene), as an example, used as a pipe
liner, has a high (>1016
Ohms/Square), resistivity factor. This
is a relatively high resistance to conductivity. This means
that any charge created internally to the pipe cannot readily
be conducted away to ground by way of the PTFE liner.
Instead the charge will be allowed to build until it exceeds
its total dielectric strength and burns a pinhole in the liner to
the internal metal wall of the casement pipe. It isn‟t charge
generation itself that is the problem, it‟s the charge
accumulation. When the rate of charge generation is greater
than the rate of charge relaxation (the ability of material to
conduct away the generated charge), charge accumulation
occurs.
The dielectric strength of PTFE is 450 to 500 volts/mil.
This indicates that for every 0.001” of PTFE liner 450 volts
of triboelectric charge will be required to penetrate the liner.
For a 2” pipeline with a 0.130” thick liner this translates into
58500 volts of triboelectric charge to burn through the liner
thickness.
When the liner is penetrated by an accumulated charge
two additional problems (time bombs) are created: 1.
Corrosive fluid (a major user of lined pipe) is now in contact
with and corroding the metal pipe wall and at some point,
depending on rate of corrosion, will fail locally causing fluid
to leak to the environment, and 2. The initial charge that
burned through the liner is now charging the outer metal
pipe, which, if continuity has not been achieved for the outer
pipe, a spark of triboelectric charge is, at some point, going
to jump to ground causing a spark.
Corrective Action
External Charge Generation
The simplest method to ensure continuity is to sand
away any primer on the back side of each flange to ensure
good metal-to-metal contact between nut and flange. Aside
from that or the use of a conductive prime paint, the current
ready-made solution to the external continuity problem is the
addition of stud bolts located in close proximity to flanges
on both pipe spools and fittings (see Fig. 3). These studs can
be applied at the factory or in the field. At each flange joint a
grounding strap (jumper) is then affixed to a stud on one
spool with a nut, extended over the flange joint and attached
to a stud on the connecting spool completing continuity
throughout the chain of connecting spools and fittings.
Figure 3 – Grounding Lug Location
Another method of creating continuity at flange joints,
while being less obtrusive and more integral, is described as
follows and represented in Fig. 4:
Referring to Fig. 4, flanges would be purchased pre-
drilled and tapped in the center of the outer edge of the
flange between the backside of the flange and the face side
of the flange. The drilled and tapped hole in each flange will
need to be centered between boltholes so that they line up
after the flange bolts are installed. The tapped hole is 1/4”
dia. x 1/2” deep.
After a flange set is installed and fully bolted the
Continuity Plate (Fig. 4) can be installed using two 1/4”
x1/2” long hex head screws and two lock washers. The
Continuity Plate has two 0.312” slotted boltholes allowing
for misalignment and movement.
The entire continuity plate assembly is relatively simple
to install, unobtrusive and establishes integral contact with
the pipeline.
12
Figure 4 – Continuity Flange Plate
Internal Charge Generation
One of the first options in preventing Internal Charge
Accumulation is by minimizing charge generation. This can
be done by adjusting the flow velocity relative to the liquid‟s
conductivity. To minimize design impact, cost and even
schedule impact on a project this needs to be evaluated early
in the project due to the possibility of a change in line size.
To retard charge generation by reducing flow velocities
British Standard (BS) suggests the following as represented
in Table 1 per BS 5958:
TABLE 1 - RECOMMENDED VELOCITIES
Liquid Conductivity BS 5958 Recommended Flow
Velocity
>1000 pS/m No restriction
50 – 1000 pS/m Less than 7 m/s
Less than 50 pS/m Less than 1 m/s
pS/m (picosiemens/meter)
If velocity reduction is not an option, or if further
safeguards against charge accumulation are warranted then a
mechanical solution to provide a path to ground for Internal
Charge Generation might be called for.
One method for conducting charge accumulation from
the interior of the pipe to ground is indicated in Figures 5 &
6. What is shown is an orifice plate made of conductive
(static dissipative) material that is compatible with the fluid
service. The orifice itself is off center to the OD of the plate
and the pipeline itself. With the shallow portion of the ID at
the invert of the pipe it allows the piping to drain in
horizontal runs.
The tab portion of the plate extends beyond the flange
OD. On the tab is a bolthole for attaching the modified
Continuity Flange Plate. The plate is designed to come in
contact with the interior surface of the liner wall as well as
protrude into the flowing fluid providing a conduit for
internally generated charge. Continuity is achieved by
attaching the plate to the flange OD that is in contact with
the piping, which is, in turn, grounded through equipment.
Figure 5 – Conductive Orifice Plate Assembly
Figure 6 – Conductivity Orifice Plate Assembly Section
Conclusion and Recommendations
It is difficult to pre-determine what fluid services and
systems will be candidates for charge accumulation
prevention and Electrostatic Discharge protection. The
simplest and most conservative answer to that is to assume
that all fluid services in lined pipe systems are susceptible.
In saying that, we then have to declare that a company‟s pipe
specifications need to reflect a global resolution that will
affect all installations.
With regard to External Charge Accumulation, the
recommendation for future installations with the least impact
would be to specify pipe with no prime coat or at least no
primer on the flanges, or a prime coat using a conductive
paint. The un-primed pipe would be primed prior to
installation with care given to primer touchup on flanges
after installation by the installing contractor or their sub.
This would better ensure spool-to-spool external continuity.
For existing installations either the studs or the
continuity plate installation would work. It can also be
suggested that the continuity plates can be tacked on to one
flange rather than drilling and tapping both flanges.
For dissipating internal charge generation the orifice
plate, as shown in Figures 5 & 6, is the only
recommendation.
PIPE FABRICATION
Entering this part of the article on fabrication does not
mean that we leave engineering behind. Indeed, the majority,
if not all, fabricators (referring to the fabricators that are
qualified for heavy industrial work) will have an engineering
staff.
13
As a project moves from the design phase into the
construction phase anyone with a modicum of project
experience can acknowledge the fact that there will most
certainly be conflicts, errors and omissions, no matter how
diligent one thinks they are during design. This is inherent in
the methodology of today‟s design/engineering process.
There are methods and approaches to design in which this
expected result can be minimized. It‟s actually a
retrospective concept, but we will save that for a future
article.
The preparation for such errors and omissions is always
prudent. If, on the other hand, the assumption is made that
the Issued for Construction design drawings will facilitate
fabrication and installation with minimal problems, then you
can expect to compound whatever problems do occur
because you weren‟t prepared to handle them. The greatest
asset a project manager can have is the ability to learn from
past experience and the talent to put into practice what they
have learned.
Fabrication
Pipe fabrication, in this context, is the construction of
piping systems by forming and assembling pipe and
components with the use of flanged, threaded, clamped,
grooved, crimped and welded joints.
In Article I we discussed the flange joint, we will
discuss the others here. There are various factors, or
considerations, that prompt the decision as to which type of
connection to use in the assembly of a piping system. To
start with, any mechanical joint is considered a potential leak
point and should be minimized. Also, the decision as to
which type of joint should be specified comes down to
accessibility requirements, installation requirements and
joint integrity. Using that as our premise we can continue to
discuss the various joining methods.
Threaded Joints
Pipe thread, designated as NPT (National Pipe Taper)
under ASME B1.20.1, is the type of thread used in joining
pipe. This is a tapered thread that, with sealant, allows the
threads to form a leak-tight seal by jamming them together
as the joint is tightened.
I described the threaded flange joint in Article I. Those
same criteria apply also to threaded fittings, in which the
benefits of the threaded joint is both in cost savings and in
eliminating the need for welding. In this regard, to
paraphrase Article I, threaded components are sometimes
used in high-pressure service in which the operating
temperature is ambient. They are not suitable where high
temperatures, cyclic conditions or bending stresses can be
potential concerns.
Hygienic Clamp Joint
The clamped joint, as mentioned in Article I, refers to
the sanitary or hygienic clamp. As you can see in Fig. 7
there are issues with this type clamp.
Figure 7 – Hygienic Clamp Joint
(Courtesy Rubber Fab Technologies Group)
Represented in Fig. 7 are three installed conditions of
the hygienic joint, minus the clamp. Joint „A‟ represents a
clamp connection that has been over tightened causing the
gasket to intrude into the ID of the tubing. This creates a
damming effect, preventing the system from completely
draining.
In joint „B‟ the clamp wasn‟t tightened enough and left
a recess at the gasket area. This creates a pocket where
residue can accumulate and cleanability becomes an issue.
Joint „C‟ represents a joint in which the proper torque
was applied to the clamp leaving the ID of the gasket flush
with the ID of the tubing.
The clamp „C‟ representation is the result that we want
to achieve with the hygienic clamp. The problem is that this
is very difficult to control on a repeatable basis. Even when
the gasket and ferrules are initially lined up with proper
assembly and torque on the joint, some gasket materials
have a tendency to creep (creep relaxation), or cold flow.
Creep relaxation is defined as: A transient stress-strain
condition in which strain increases concurrently with the
decay of stress. More simply put, it is the loss of tightness in
a gasket, measurable by torque loss.
Cold Flow is defined as: Permanent and continual
deformation of a material that occurs as a result of
prolonged compression or extension at or near room
temperature.
There have been a number of both gasket and fitting
manufacturers that have been investing a great deal of
research in attempting to resolve this issue with the clamp
joint. Some of the solutions regarding fittings were
14
addressed in Article I. Additionally, gasket manufacturers,
and others have been working on acceptable gasket materials
that have reduced creep relaxation factors, as well as
compression controlled gasket designs.
When mentioning acceptable gasket material in the
previous paragraph, what I am referring to is a gasket that is
not only compatible with the hygienic fluid service, but also
meets certain FDA requirements. Those requirements
include Gasket material that complies with USP Biological
Reactivity Test #87 & 88 Class VI for Plastics and FDA
CFR Title 21 Part 177.
Grooved Joint
The grooved joint (Fig. 8), from simply a static internal
pressure containment standpoint, is as good as or, in some
cases superior to the ASME Class 150 flange joint. In the
smaller sizes, 1” through 4” the working pressure limit will
be equal to that of a Class 300, carbon steel, ASTM A105,
ASME B16.5 flange.
Its main weakness is in its allowable bending and
torsional stress at the coupling. This can be alleviated with
proper support. Because of this design characteristic the
manufacturers of grooved joint systems have focused their
efforts and created a niche in the fire protection and utility
fluid service requirements, with the exception of steam and
steam condensate.
This type of joint is comparatively easy to install and
enhances that fact in areas that would require a fire card for
welding. Since no welding is required modifications can be
made while operation continues. Some contractors choose to
couple at every joint and fitting, while others choose to
selectively locate couplings, much as you would selective
locate a flange joint in a system. It‟s a decision that should
be made based on the particular requirements or preference
of a project or facility.
Figure 8 – Grooved Pipe & Coupling
(Courtesy Victaulic)
Pressed Joint
The pressed joint is actually a system that uses thin wall
pipe, up through 2” NPT, to enable the joining of pipe and
fittings with the use of a compression tool. Welding is not
required and threading is only necessary when required for
instrument or equipment connection.
Figure 9 – Pressed Joint
(Courtesy Victaulic)
These types of systems are available from various
manufacturers in carbon steel, 316 and 304 stainless steel
and copper. Because of the thin wall pipe corrosion
allowance becomes a big consideration with carbon steel.
While the static internal pressure rating of these systems
is comparable to an ASME Class 150 flange joint there are
additional fluid service and installation characteristics that
need to be considered. With axial and torsional loading
being the weak spot in these systems they are not practical
where water hammer is a potential, such as in steam
condensate. The axial load consideration carries over to
supporting the pipe as well. Ensure that vertical runs of this
pipe are supported properly from beneath. Do not allow
joints in vertical runs to be under tension. They must be
supported properly from the base of the vertical run.
Welded Joint
The welded joint is by far the most integrated and
secure joint you can have. When done properly it is as strong
as the pipe itself. The key to a weld‟s integrity lies in the
craftsmanship of the welder or welding operator, the
performance qualification of the welder or welding operator,
and the weld procedure specification.
Before I go further I want to explain the difference
between the terms welder and welding operator. A welder is,
as you might have guessed, someone who welds. To be more
precise, it is someone who welds by hand, or manually. A
welding operator is someone who operates an automatic
welding machine. The ends of the pipe still have to be
prepared and aligned, and the automatic welding machine
has to be programmed.
The advantage of machine welding is apparent in doing
production welds. This is shop welding in which there is a
quantity of welds to be made on the same material type, wall
thickness and nominal pipe size. Once the machine is set up
15
for a run of typical pipe like this it is very efficient and
consistent in its weld quality.
This is another topic that could easily stand alone as an
article, but we won‟t do that here. Instead we will focus on
some of the primary types of welding used with pipe. Those
types include:
1. GMAW (Gas Metal Arc Welding) or MIG
2. GTAW (Gas Tungsten Arc Welding) or TIG
3. SMAW (Shielded Metal Arc Welding) or MMA or
Stick Welding
4. FCAW (Flux Cored Automatic welding)
GMAW: Most often referred to as MIG, Metal Inert
Gas welding, GMAW (Gas Metal Arc Welding) can be an
automatic or semi-automatic welding process. It is a process
by which a shielding gas and a continuous, consumable wire
electrode is fed through the same gun (Fig. 10). The
shielding gas is an inert or semi-inert gas such as argon or
CO2 that protects the weld area from atmospheric gases,
which can detrimentally affect the weld area.
There are four commonly used methods of metal
transfer used in GMAW. They are:
1. globular,
2. short-circuiting,
3. spray, and
4. pulsed-spray
With the use of a shielding gas the GMAW process is
better used indoors or in an area protected from the wind. If
the shielding gas is disturbed the weld area can be affected.
Figure 10 – GMAW (MIG) Welding
(Courtesy The Welding Institute)
GTAW: Most often referred to as TIG, Tungsten Inert
Gas welding, GTAW (Gas Tungsten Arc Welding) can be
automatic or manual. It uses a nonconsumable tungsten
electrode to make the weld (Fig. 11), which can be done
with filler metal or without filler metal (autogenous). The
TIG process is more exacting, but is more complex and
slower than MIG welding.
In Article 1 I mentioned the use of orbital welding for
hygienic tube welding. Orbital welding uses the GTAW
method. Once the orbital welder is programmed for the
material it is welding it will provide excellent welds on a
consistent basis. Provided, that is, that the chemistry of the
base material is within allowable ranges.
Figure 11 – GTAW (TIG) Welding
(Courtesy The Welding Institute)
A wide differential in sulfur content between the two
components being joined can cause the weld to drift into the
high sulfur side. This can cause welds to be rejected due to
lack of full penetration.
SMAW: Also referred to as MMA, Manual Metal Arc
welding, or just simply Stick welding, SMAW (Shielded
Metal Arc Welding) is the most common form of welding
used. It is a manual form of welding that uses a consumable
electrode, which is coated with a flux (Fig. 12). As the weld
is being made the flux breaks down to form a shielding gas
that protects the weld from the atmosphere.
The SMAW welding process is versatile and simple,
which allows it to be the most common weld done today.
Figure 12 – SMAW (Stick) Welding
(Courtesy The Welding Institute)
FCAW: Flux Cored Arc Welding is a semiautomatic or
automatic welding process. It is similar to MIG welding, but
the continuously fed consumable wire has a flux core. The
flux provides the shielding gas that protects the weld area
from the atmosphere during welding.
Welding Pipe
The majority of welds you will see in pipe fabrication
will be full penetration circumferential buttwelds, fillet
16
welds or a combination of the two. The circumferential
buttwelds are the welds used to weld two pipe ends together
or other components with buttweld ends. Fillet welds are
used at socketweld joints and at slip-on flanges. Welds in
which a combination of the buttweld and fillet weld would
be used would be at a stub-in joint or a joint similar to that.
A stub-in joint (not to be confused with a stub-end) is a
connection in which the end of a pipe is welded to the
longitudinal run of another pipe (Fig. 13). Depending on
what the design conditions are this can be a reinforced
connection or an unreinforced connection. The branch
connection can be at 90º or less from the longitudinal pipe
run.
Figure 13 – Sample Stub-In Connections
(Courtesy ASME B31.3)
Hygienic Fabrication and Documentation
Hygienic and semiconductor pipe fabrication uses
automatic autogenous welding in the form of orbital
welding. This, as explained in Article I, is a weld without the
use of filler metal. It uses the orbital welding TIG process. In
some cases hand welding is required, but this is kept to a
minimum, and will generally require pre-approval.
When fabricating pipe for hygienic services it will be
necessary to comply with, not only a specific method of
welding, but also an extensive amount of documentation. As
mentioned in Article I, developing and maintaining the
required documentation for hygienic pipe fabrication and
installation can add an additional 30% to 40% to the piping
cost of a project.
The documentation needed, from the fabrication effort
for validation, may include, but is not limited to:
1. Incoming Material Examination Reports
2. Material Certification
a. MTR‟s
b. Certification of Compliance
3. Weld Gas Certification
4. Signature Logs
5. WPQ‟s (Welder & Welding Operator Performance
Qualification)
6. Welder & Welding Operator Inspection Summary
7. Mechanical and electropolishing procedures
8. Examiner Qualification
9. Inspector Qualification
10. Welder Qualification Summary
11. Gage Calibration certifications
12. Weld Continuity Report
13. WPS‟s (Weld Procedure Specifications)
14. PQR‟s (Procedure qualification Record)
15. Weld Coupon log
16. Weld Maps
17. Slope Maps
18. Weld Logs
19. Leak Test Reports
20. Inspection reports
21. Passivation Records
22. Detail mechanical layouts
23. technical specifications for components
24. As-Built Isometrics
25. Original IFC isometrics
26. Documentation recording any changes from IFC to
As-Build isometrics
The above listed documentation, which closely parallels
the list in ASME-BPE, is that which is generally required to
move an installed hygienic system through validation,
commissioning and qualification (C & Q). And this isn‟t all
that‟s required. There is additional supporting
documentation such as P&ID‟s, procedural documents, etc.
that are also required. Depending on the size and type of a
project it can be a massive undertaking. If not properly set
up and orchestrated it can become a logistical nightmare.
What you do not want to do is discover during C&Q
that you are missing a portion of the required
documentation. Resurrecting this information is labor
intensive and can delay a project‟s turn-over significantly. I
cannot stress it strongly enough just how imperative it is that
all necessary documentation be identified up front. It needs
to be procured throughout the process and assimilated in a
turnover package in a manner that makes it relatively easy to
locate needed information while also allowing the
information to be cross indexed and traceable within the TO
package.
The term validation is a broad, generalized, self-
defining term that includes the act of commissioning and
qualification. Commissioning and qualification, while they
go hand in hand, are two activities that are essentially
distinct within themselves.
For this article I will go no further with the topic of
Validation, Commissioning and Qualification. This is a topic
that I will touch on again in Article III.
Future Articles
The third and final article in this series, titled “Piping
Design Part III – Installation, Cleaning, Testing and
Verification”, will wrap up the series by discussing the four
title points.
Acknowledgement:
17
I wish to thank Earl Lamson, Senior Project Manager
with Eli Lilly and Company, for being kind enough in taking
time out of a busy schedule to read through the draft of this
second article. Earl has a remarkable set of project and
engineering skills that set him apart from many I have
worked with. That and the fact that I value his opinion are
the reasons I asked him to review this article.
About the author:
W. M. (Bill) Huitt has
been involved in industrial
piping design, engineering
and construction since 1965.
Positions have included
design engineer, piping design
instructor, project engineer,
project supervisor, piping
department supervisor,
engineering manager and
president of W. M. Huitt Co. a
piping consulting firm
founded in 1987. His experience covers both the engineering
and construction fields and crosses industrial lines to include
petroleum refining, chemical, petrochemical,
pharmaceutical, pulp & paper, nuclear power, biofuel, and
coal gasification. He has written numerous specifications,
guidelines, papers, and magazine articles on the topic of pipe
design and engineering. Bill is a member of ISPE
(International Society of Pharmaceutical Engineers), CSI
(Construction Specifications Institute) and ASME
(American Society of Mechanical Engineers). He is a
member of three ASME-BPE subcommittees, several Task
Groups, an API Task Group, and sets on two corporate
specification review boards. He can be reached at:
W. M. Huitt Co.
P O Box 31154
St. Louis, MO 63131-0154
(314)966-8919
www.wmhuitt.com
As published in the September and October 2007 issues of Chemical Engineering Magazine
Efficiency, quality and safety are the imperatives that are factored in when considering field fabrication, but
don’t forget cost. W. M. (Bill) Huitt
W. M. Huitt Co.
As the title implies this article will discuss the
Installation, Cleaning, Testing and, to a lesser degree,
Validation of piping systems. I say to a lesser degree with
Validation because Validation is a very complex, often
proprietary and exceedingly difficult-to-define topic. Rather
than delve into it in great detail as part of a multi-topic
article I will attempt to simply provide some understanding
as to its function and need.
PIPE INSTALLATION
But first things first, the installation of pipe follows its
fabrication and is very frequently a part of it. The installation
of pipe can be accomplished in the following four primary
ways, or combinations thereof:
1. Field fabricate and install,
2. Shop fabricate and field erected,
3. Skid fabrication, assembly & installation, and
4. Modular construction
I would like to assure you that I am not going to diverge
off into fabrication again since we discussed it, although
somewhat briefly, in Article II. I am including fabrication in
this article simply because fabrication is such an integral part
of pipe installation.
FIELD FABRICATE AND INSTALL
Field fabrication and installation is just what it implies.
The pipe is fabricated on site either in place or in segments
at an on-site field fabrication area and then erected. A
number of factors will dictate whether or not it is feasible to
field fabricate: The size and type of the project, pipe size and
material, the facility itself, weather conditions, availability
of qualified personnel, existing building operations,
cleanliness requirements, time available to do the work, etc.
Efficiency, quality and safety are the imperatives that
are factored in when considering field fabrication. And
before you think I missed it, cost is the fallout of those
factors. Logistically speaking, if all pipe could be fabricated
on-site in a safe and efficient manner, maintaining quality
while doing so, it would make sense to do it in that manner.
However, before making that final decision, let’s look at
some of the pros and cons of field fabrication:
Pros:
1. Only raw material (pipe, fittings, valves, etc.)
need to be shipped to the site location. This is
much easier to handle and store than multi-plane
configurations of pre-fabricated pipe.
2. No time-consuming need to carefully crib, tie-
down and chock pre-fabricated *spool pieces for
transport to the job site.
3. Reduced risk of damage to spool pieces.
4. More efficient opportunity to fab around
unexpected obstacles (structural steel, duct,
cable tray, etc.)
5. Fabricate-as-you-install reduces the rework risk
assumed when pre-fabricating spools, or the cost
Piping Design Part 3:
Installation, Cleaning,
Testing & Verifification
2
related to field verification prior to shop
fabrication.
6. The field routing installation of pipe through an
array of insufficiently documented locations of
existing pipe and equipment, on a retrofit
project, is quite frequently more effective than
attempting to pre-fabricate pipe based on
dimensional assumptions. *Spool pieces are the pre-fabricated sections of pipe that are fabricated and numbered in the fab shop then shipped to the job site
for installation.
Cons:
1. Weather is arguably the biggest deterrent. If the
facility under construction is not enclosed then
protection from the elements will have to be
provided.
2. When welding has to be done in conditions that
are not environmentally controlled then pre-
heating will be required if the ambient
temperature (not the metal surface temperature)
is 0° F or below.
3. In a new facility, as opposed to having to route
piping through an array of poorly located
existing pipe and equipment, field fabrication of
buttwelded pipe is not as efficient and cost
effective as shop fabrication.
4. Concerns about safety and efficiency when
working in a facility while it is in operation in
advance of a turnaround or to begin advance
work on a plant expansion.
Generally speaking, threaded, socketweld, grooved, and
other proprietary type joints that do not require buttwelding
are field fabricated and installed. Buttwelding of small, 1
1/2” NPS and less, are very often field fabricated and
installed because of the added risk of damage during
transport, in pre-fabricated form, from the shop to the site.
SHOP FABRICATE AND INSTALL
Shop fabrication is, generally speaking, any pipe,
fittings and components that are assembled by welding into
spool assemblies at the fabricator’s facility. The spools are
then labeled with an identifier and transported to the job site
for installation.
Each spool piece needs its own identifier marked on the
piece itself in some fashion that will make it easy to know
where its destination is in the facility and/or where it belongs
in a multi-spool system of pipe. This will allow the installer
to efficiently stage the piece and ready it for installation.
As part of the process of developing spool sections
field-welded joints need to be designated. These are welded
joints that connect the pre-fabricated spools. In doing this
the designer or fabricator will identify two different types of
field-welded joints.
One is a Field Weld (FW) and the other is a Field
Closure Weld (FCW). The FW indicates a joint in which the
end of a pipe segment is prepared for the installer to set in
place and weld to its connecting joint without additional
modification in the field. This means that the length of pipe
that is joined to another in the field is cut precisely to length
and the end prepared in the shop for welding.
The FCW provides the installer with an additional
length of pipe, usually 4” to 6” longer than what is indicated
on the design drawings, to allow for field adjustment.
What has to be considered, and what prompts the need
for a FCW, is the actual, as-installed, location of both the
fixed equipment that the pipe assemblies may connect to and
the actual installed location of the pipe assembly itself. Odds
are that all equipment and piping will not be installed
exactly where indicated on design drawings.
The dimensional location of the equipment items given
on design drawings is not a finite location, they are merely
intended locations, as are drawings for building steel, pipe
supports and others. What factors into the installation of
shop fabricated pipe is the actual location of the equipment
nozzle it will be connecting to in relation to the pipe’s
installed location.
In connecting to equipment there is a build-up, or stack-
up, of tolerances that will effectively place the actual, or
final, location of the nozzle at some point in the xyz
geometry of three-dimensional space, other than where the
design drawing indicates. The tolerance stack-up comes
from the following:
1. Manufacturing tolerances in material forming,
nozzle location, and vessel support location.
2. The actual set-in-place location of the vessel.
3. Load cell installation (when applicable).
4. The actual set-in-place pipe run-up location.
In order to allow for these inevitable deviations between
the drawing dimensions used to fabricate the vessel, set the
vessel, and install the pipe assembly, and the actual installed
location of the connecting points, a field closure piece, or
two, will be required for that final adjustment.
The field closure piece is a designated section of the
pipe assembly in which a field weld has been indicated. The
section with the field closure weld would be the length
required to agree with that indicated on the design drawing,
plus an additional 4” to 6” (more or less depending on
fabricator’s comfort level with the equipment locations).
What this does is allow the field to make the final
determination in the adjustments when connecting to fixed
equipment.
SKID (SUPER SKID) FABRICATION
3
A skid is a pre-packaged assembly that may contain all
or some of the following that make up an operating system:
vessels, rotating equipment, piping, automation components,
operator interfaces, instrumentation, gages, electrical panels,
wiring and connectors, framework, supports, in-line piping
components, and insulation. A single process or utility
system may fit onto one skid or, depending on size
restraints, may comprise multiple skids.
After fabrication of a skid is complete it will typically
go through Factory Acceptance Testing (FAT) at the
fabricator’s facility. The skid is then shipped to the job site
where it is installed in its final location. After installation it
would typically go through a follow-up Site Acceptance Test
(SAT), including additional hydro-testing. This is basically a
system shake-down to determine that everything is intact,
and that those things that did not remain intact during
transport are discovered and repaired.
Logistics and the necessary skill-set required for the
installation, connection and start-up of a particular skid
package will dictate to what extent the skid fabricator will be
involved after it is shipped to the job site.
MODULAR CONSTRUCTION
The term module or modular construction is quite often,
in this context, interchanged with the term skid fabrication.
A module can refer to pre-fabricated units that actually form
the structure of a facility as each is installed. Or, the units
may be smaller sub-assemblies that, when combined, make
up a complete process or utility system.
Modules too consist of all or some of the following:
vessels, rotating equipment, piping, automation components,
HVAC, instrumentation, electrical wiring and connectors,
framework, walls, architectural components, lighting,
supports, in-line piping components, and insulation. This, as
an example, allows a complete locker room module to be
placed and connected to a complete water treatment module.
The smaller sub-assembly modules, in many cases, are
interchanged with the term skid. It saves on misperception
when a company defines these terms, both for internal
discussion and for the purpose of making it clear to outside
contractors, as to what is meant when using the term
module.
INSTALL APPROACH
Now that we have a general idea of the four primary
approaches to piping installations how do we decide which
is the best method, or combination of methods, to use for a
particular project? But there is one major caveat I would like
to address before launching into this subject.
Each project is individualized with its own particular set
of decision drivers with regard to a selected execution
approach. There are no hard and fast rules for determining a
best approach at job execution. It requires experienced
personnel assigning values to the various aspects of project
execution, overlaying a timeline, and then assessing
logistics. Sounds simple, but is in actuality can be a very
complex process.
What I am attempting to say here is, that the following
is a guideline and not hard and fast rules. There are simply
too many project variables and complexities to allow it.
In approaching this decision keep in mind that the
method of installation needs to be weighed against a
contractor’s preferred methodology. In saying that I am not
implying that the contractor’s preferred methodology should
drive your decision on how to execute a job. On the
contrary, once you determine how the job needs to be
executed you then look to only those contractors whose
preferred methodology agrees with your project execution
plans.
Some contractors prefer to do most, if not all fabrication
in the shop, others prefer to set up at the job-site, while
others are flexible enough to utilize the best of both
methods.
The three main criteria, efficiency, quality and safety
indicated earlier under “Field Fabricate and Install”, would
apply here as well. Using those three elements as a basis for
making our determination let us look at some common
variables:
1. Environment
a. Controlled environment
b. Open to the elements
2. Industry
a. Pharmaceutical
b. Biopharmaceutical
c. Semiconductor
d. Food & Dairy
e. Petroleum refining
f. Bulk chemical
g. Pulp & paper
h. Off-Shore
i. Pipeline
j. Power generation
3. Type of project
a. Retrofit
b. Fast track approach
c. New (Grassroots/Greenfield) project
d. Clean-build
e. Single level
f. Multi-level
g. Room repetition
4. Range of pipe material and sizes
a. Small percentage of alloy pipe
b. Large percentage of alloy pipe
c. Large % of large pipe sizes
4
d. Large % of small pipe sizes
e. Mix of small and large pipe sizes
5. Location
a. Close to metropolitan area
b. Remote location
c. Country with limited resources
Environment
The environment is only a factor when work has to be
done in an open-air structure or other outdoor installation
(tank farm, pipeline, pipe rack or yard piping, etc.). Working
in an open air structure will require protection from the
elements (rain, snow, wind, cold, etc.). There may
additionally be a requirement to work in elevated areas on
scaffolding and otherwise. All of this can have a potential
impact on safety and efficiency.
Pipe rack installation consists mainly of straight runs of
pipe, and will not necessarily have a requirement or need for
pre-fabrication. That is, unless it is pre-fabricated as modular
skid units. Depending on the project it could be cost
effective on an overall strategic basis to modularize the pipe
rack, steel and all.
The big advantage to shop fabrication is the controlled
environment in which it’s done. This includes the Quality
Control aspect, better equipment (generally speaking), a
routine methodology of how a piece of work progresses
through the shop, and better control, through a developed
routine, of required documentation.
Industry
I know this is generalizing, but we can group the
various industries into clean/indoor build and non-
clean/outdoor build. There are exceptions to this, but under
clean/indoor build we can list the following;
Clean/Indoor build
a. Pharmaceutical
b. Biopharmaceutical
c. Semiconductor
d. Food & Dairy
Under non-clean/outdoor build we can list the
following;
Non-Clean/Outdoor Build
a. Petroleum refining
b. Bulk chemical
c. Pulp & paper
d. Off-Shore
e. Pipeline
f. Power generation
The clean build philosophy comes from the need to
construct certain facilities with a more stringent control on
construction debris. Those industries listed above under
Clean/Indoor Build often require a facility, at least a portion
of a facility, to be microbial and particulate free, as
stipulated by the design.
There can be no debris, organic or inorganic, remaining
after construction in accessible or inaccessible spaces of the
facility. Of particular concern with the pharmaceutical,
biopharm and food 7 dairy is food waste and hidden
moisture. Food waste can entice and support rodents and
insects, and hidden moisture can propagate mold, which can
eventually become airborne. If not discovered until the
facility is in operation the impact, upon discovery, can
potentially be devastating to production.
Such contamination can be discovered in one of two
ways. Discovery at the source, possibly behind a wall or
some other out-of-the-way place, means that not only does
current production have to cease, but product will have to be
analyzed for possible contamination. Once found it hen has
to be remediated.
The other method of discovery comes from the
continuous testing and validation of the product stream. If a
contaminant is discovered in the product the production line
is stopped and the problem then becomes an investigation in
to finding the source of the contamination.
The clean-build philosophy therefore dictates more
stringent and strict requirements for controlling and
inspecting for debris on an ongoing basis throughout
construction and start-up.
It will be necessary, on a clean-build site, to follow
some rather simple rules:
1. Smoking or smokeless tobacco products of any
kind are not allowed on the site property,
2. Off site break and lunch areas, no food or drink,
other than water, allowed on the site premises,
3. Do not begin installing pipe, duct or equipment
until, at the very least, a roof is installed,
4. After roof and walls are installed ensure that
there is no standing water remaining in the
facility,
5. Prior to and during the construction of hollow
walls, such as those framed and dry-walled,
ensure on a daily basis that there is no moisture
or debris in the wall cavity,
6. Duct work delivered to the job site shall have the
ends covered with a plastic sheet material, which
shall remain on the ends until connected in place,
7. Fabricated pipe delivered to the job site shall
have the ends covered in a suitable fashion with
suitable material, and shall remain on the ends
until connected in place,
8. During and after flushing and testing of pipelines
all water spills shall be controlled to the extent
possible and shall be cleaned up after flushing
and testing or at the end of the work day,
5
Type of Project
While the type of project is not the main influence in
determining how you approach the execution of a project it
does play a key role. It will help drive the decision as to how
the piping should be fabricated and installed.
As an example, if the project is a retrofit it will require
much of the pipe, regardless of size and joint connection, to
be field fabricated and installed. This is due simply to the
fact that the effort and cost necessary to verify the location
of all existing pipe, equipment, walls, columns, duct, etc. in
a somewhat precise manner, would not be very practical.
You would be better served by field verifying the
approximate location of the above items with existing
drawings, for planning and logistic purposes, then shop or
field fabricate, verify and install as you go.
A fast track project, one that has a compressed schedule,
will require parallel activities where possible. Whereas shop
and skid fabrication would be utilized as much as possible
simply to expend more man-hours over a shorter time period
while attempting to maintain efficiency. Even though there
may be added cost to this approach. This approach is time
driven and not budgetary driven.
A new grassroots facility still requires routing
verification as you go, but certainly not the much more
involved need to locate previously installed obstructions as
needs to be done when working with an existing facility.
If the project is a clean-build project (typical for the
pharmaceutical, biopharmaceutical, semiconductor and food
& dairy industries) inside an environmentally controlled area
it will be more practical to shop fabricate or utilize skid or
modular fabrication for most, if not all of the piping. This
will reduce the number of personnel and the amount of
fabrication debris in the facility, and provide better control
for keeping it out of the pipe itself. With personnel you
could have food wrappers, drink cans and bottles, food
waste, and clothing items. Fabrication debris could include
metal filings, cutting oil, pieces of pipe, weld rod and weld
wire remnants, etc.
If the project is not a clean-build, but is still inside an
environmentally controlled facility the same logic does not
necessarily apply. The decision to shop fab and install or to
field fab and install becomes one based on efficiency rather
than how best to maintain a clean area. And that’s not to say
that if it doesn’t qualify as a clean-build project then the
construction debris can just be allowed to pile up.
There is still safety and efficiency to be concerned with
on any project and a clean job site is a major part of that.
Maintaining a clean job site is an integral component of
good project execution.
Keeping personnel and equipment to a minimum at the
job site is not an absolute, but is one of the key
considerations to the efficiency of pipe installation.
Following that logic most of the buttwelded pipe should be
shop fabricated. A couple of things to consider, when
determining which buttwelded pipe to shop fabricate, is size
and material.
Range of Pipe Material and Sizes
Shop fabricated spools need to be transported to the job
site. This requires handling. Handling and transporting small
diameter pipe and/or thin-wall tubing spools creates the
potential for damage to those spools.
If you are shop fabricating everything and the distance
from shop to site is simply across town the risk to damaging
small diameter pipe spools is a great deal less than if they
have to be shipped half way across the US, Europe or Asia.
Or even across an ocean.
In transporting spools over long distances, unless there
is a great deal of thought and care given to cribbing the load
of spools, it may not be beneficial to transport buttwelded
pipe spools NPS 1 ½” and less. It may be more practical to
fabricate these sizes on site, unless you are fabricating
hygienic or semi-conductor piping. These types of systems
require a great deal more control and a cleaner fabrication.
Meaning that pipe fabrication will require a clean shop area
on-site, or the pipe will need to be fabricated at an off-site,
better controlled shop facility.
A practical rule of thumb in determining what to shop
fab and what to field fab follows in Table 3-1:
Table 3-1 Shop and Field Fabrication
Size (in) Material Joint Shop/Field
≤ 1 ½ Pipe 1, 2, 3, 6 Field
≤ 1 ½ Pipe 4 & 5 Shop
≥ 2 Pipe 3 & 6 Field
≥ 2 Pipe 4 & 5 Shop
≤ 1 Tubing 5 Field
≤ 1 Tubing 5 Shop (a, b)
≥ 1 ½ Tubing 5 Shop Joint Type:
1 = Socketweld
2 = Threaded 3 = Grooved – Fully (Grooved fittings and pipe ends.)
4 = Grooved – Partially (Shop-welded spools with grooved ends.)
5 = Buttweld 6 = Flanged – Lined or unlined Pipe
Notes:
a. Hygienic tubing b. Special cribbing and support for transport
The above Table 3-1 is a general methodology. Dictates
of the project and a contractors SOP will determine how best
to define what gets shop fabricated and what gets field
fabricated.
6
Petroleum refining and bulk chemical projects are
generally open air projects in which field fabrication and
installation of pipe is exposed to the elements. While a clean
build is not a requirement on these types of projects
efficiency and, above all, safety is, as it is on any type
project. Because of this, it would make sense to utilize shop
fabrication as much as possible.
Fabricating pipe spools under better controlled shop
conditions will provide improved efficiency and safer per
hour working conditions over what you will generally find in
the field. This translates into fewer accidents.
Referring back to Table 3-1, with respect to the
potential for damage during transport, pipe sizes NPS 2” to
3” and larger ship much better than smaller pipe sizes.
Particularly when working with thin-wall tubing. This is a
consideration when determining what to shop fab and what
to field fab.
Location
Job site location is one of the key markers in
determining shop or field fabrication. In many cases building
a facility in a remote location will be a driver for utilizing a
disproportionate amount of skid or module fabrication.
Disproportionate in the sense that project management may
look at modularizing the entire job, rather than mobilize the
staffing and facilities needed to fab and install on or near the
job site. This would constitute a larger amount of
modularization over what might normally be expected for
the same type project in a more metropolitan region, or an
area with reasonable access to needed resources.
To expand on that thought; it was pointed out to me by
Earl Lamson, Senior Project Manager with Eli Lilly and
Company, an observation I fully agree with, that project
resources, even in metropolitan areas, are quite frequently
siloed around a specific industry. In certain regions of the
US for example, you may discover that there are an
abundance of craftsman available when building a refinery,
but that same region may have difficulty, from a trained and
experienced personnel perspective, in supporting the
construction of a semiconductor facility.
Consequently when building a pharmaceutical facility in
another region you may find a sufficient population of
trained and experienced craftsman for that industry, but may
not find that resource adequate when building a chemical
plant.
Building a project in a remote location requires the
project team to rethink the job-as-usual methodology. From
a logistics standpoint mobilization of personnel and material
become a major factor in determining the overall execution
of such a project. Project planning is a big component in
project execution, but is more so when attempting to build in
remote areas. And this doesn’t even touch on the security
aspect.
Nowadays, when constructing in any number of remote
areas, security is a real concern that requires real
consideration and real resolution. Reduced on-site staffing is
a good counter-measure in reducing risk to personnel when
building in remote or even non-remote third-world areas.
PIPE SYSTEM CLEANING
While there are requirements in ASME for leak testing
cleaning requirements do not exist. In ASTM A 380 & 967
you will find Standards on cleaning, descaling and
passivation, but nothing in ASTM on simply flushing and
general cleaning. Defining the requirements for the internal
cleaning of piping systems falls within the responsibilities of
the Owner.
The term “cleaning”, in this context, is a catch-all term
that also includes flushing, chemical cleaning, and
passivation. So before we go further let me provide some
definition for these terms as they apply in this context. I say,
“as they apply in this context”, because these terms are
somewhat flexible in their meaning, depending on source
and context, and could be used to describe activities other
than what is intended in this dialog.
Definitions
Cleaning: A process by which water, solvents, acids or
proprietary cleaning solutions are flushed through a piping
system to remove contaminants such as cutting oils, metal
filings, weld spatter, dirt, and other unwanted debris.
Flushing: A process by which water, air or an inert gas
is forced through a piping system either in preparation for
chemical cleaning or as the only cleaning process. Flushing
can be accomplished by using dynamic pressure head or
released static pressure head, as in a fill-and-dump
procedure. Blow-down can be considered as flushing with a
gas.
Passivation: A process by which a chemical solution,
usually with a base of nitric, phosphoric, citric acid or other
mild oxidant, is used to promote or accelerate the formation
of a thin (25 to 50 Angstroms) protective oxide layer (a
passive layer) on the internal surface of pipe, fittings and
equipment. In stainless steels, the most commonly used alloy
at present, it removes any free iron from the pipe surface to
form a chromium-rich oxide layer to protect the metal
surface from aggressive liquids such as high purity waters.
Note: Cleaning and Flushing can be interchanged when the process
only requires water, air or an inert gas to meet the required level of
cleanliness. When the term “cleaning” is used in this context it may
infer what is defined as flushing.
Cleaning and Testing
7
With regard to cleaning and leak testing, and which to
do first, there are drivers for both and different schools of
thought on the overall process. Each contractor will have
their preference. It is in the Owner’s best interest to
determine their preference or be at risk in just leaving it to
the contractor. In either case you should have a line of
thought on the process, if for no other reason than to be able
to understand what it is the contractor is proposing to do.
At the very least, in advance of leak testing, perform
either a basic flush of a *test circuit, or perform an internal
visual examination as the pipe is installed. A walk-down of
the test circuit should be done just prior to filling the system
with any liquid. The last thing you want to happen is to
discover too late that a joint wasn’t fully connected or an in-
line component was taken out of the pipeline. In a facility
that is not a clean-build it can simply be a mess that has to
be cleaned up. In a clean-build facility an incident such as
this can potentially be costly and time-consuming to
remediate.
Note: *refer to the following section on “Leak Testing”
Before getting into further specifics of this discussion
we need to define some general cleaning and testing
procedures and assign them some easy to use indicators. In
this way it will be much easier to discuss the various
processes. We can then work through some general
scenarios and see which sequencing works best.
Following is a list of cleaning requirements:
Table 3-2 – General Cleaning Scenarios
Category Description
C-1 Flush only (water, air or inert gas)
C-2 Flush, clean with cleaning solution, flush
C-3 Clean with cleaning solution, flush
C-4 Flush, clean, passivate, flush
Following is a list of leak testing requirements:
Table 3-3 – General Leak Testing Scenarios
Category Description
T-1 Initial service leak test
T-2 Hydrostatic leak test
T-3 Pneumatic leak test
T-4 Sensitive leak test
T-5 Alternative leak test
While the cleaning descriptions are self explanatory the
leak testing descriptions may not be. Please refer to the
following section on “Leak Testing” to find clarification of
the terms used in Table 3-3.
One other thing I would like to mention before we go
on. Since we are discussing new pipe installation we will not
include steam-out cleaning or pipeline pigging. These are
cleaning procedures that are used on in-service piping to
clean the fluid service residue build-up from interior pipe
walls after a period of use.
Before subjecting the system to an internal test pressure
the piping should first be walked down to make certain, as
mentioned earlier, that there are no missing or loose
components. The system is then flushed with water or air to
make sure that there are no obstacles in the piping. Over the
years we have discovered in installed piping systems
everything from soda cans to shop towels, work gloves, nuts
& bolts, weld rod, Styrofoam cups, candy wrappers, and
other miscellaneous debris including dirt and rocks.
After this initial flush, which could also be the only
flush and cleaning required, the system is ready for chemical
cleaning or to leak test. In large systems it may be beneficial
to leak test smaller test circuits and then perform a final
cleaning once the entire system is installed and tested. This
would include a final completed system leak test that would
test all of the joints that connect the test circuits. That is,
unless these joints were tested as the assembly progressed.
If it is decided, on large systems, to leak test smaller
segments, or test circuits as they are installed, prior to
flushing the entire system, the piping needs to be examined
internally as it is installed. This is to prevent any large debris
items, as listed above, from remaining in the piping during
the test.
Now that we have touched on those generalities let’s
take a look at each of the cleaning Categories listed in Table
3-2 and see how to apply them.
Cleaning Category C-1 is simply a flush with water, air
or inert gas. The one non-manual assist that water requires in
order for it to clean the inside of a piping system is velocity.
But what velocity is necessary?
The main concept behind flushing a pipeline is to
dislodge and remove suspected debris. In order to dislodge,
suspend and remove this unwanted material in the piping
system it is necessary that water or air be forced through the
piping system at a velocity sufficient to suspend the heaviest
suspected particles and move them along the pipeline.
The velocity required to suspend the particles and move
them along the pipeline for removal is dependent upon their
size and weight, and the flush medium. Metal filings,
arguably the heaviest particles normally found in newly
fabricated pipe, will have a terminal mid-range settling
velocity, in water, of approximately 10 feet per second.
Therefore, a flushing velocity of approximately 10 feet per
second should be achieved during the flush. (This does not
apply to acid cleaning.)
8
The following Table 3-4 indicates the rate of flow
required to achieve approximately 10 feet per second of
velocity through various sizes and schedules of pipe.
Table 3-4 – Rate of Flushing Liquid Needed to Maintain
Approximately 10 FPS Velocity (GPM)
Pipe Pipe Sizes (inches)
Sch. ½ ¾ 1 1 ½ 2 3 4
5s 12 20 34 77 123 272 460
40 10 16 27 64 105 230 397
80 7 13 22 55 92 ─ ─
Purging a piping system clear of debris with air requires
a velocity of approximately 25 feet per second. The
following Table 3-5 indicates the rate of air flow required to
achieve approximately 25 feet per second of velocity through
various sizes and schedules of pipe.
Table 3-5 – Rate of Air Flow to Maintain Approx 25 FPS Velocity
(SCFS)
Pipe
Sch
Pipe Sizes (inches)
½ ¾ 1 1 ½ 2 3 4
Press
15
psig
5s 0.14 0.23 0.39 0.86 1.39 3.06 5.17
40 0.11 0.19 0.30 0.71 1.18 2.59 4.47
80 0.08 0.15 0.25 0.62 1.04 2.32 4.03
Press
50
psig
5s 0.30 0.51 0.84 1.88 3.02 6.67 11.3
40 0.23 0.41 0.66 1.56 2.56 5.65 9.73
80 0.18 0.33 0.55 1.35 2.26 5.05 8.79
One thing you might notice is that the size range only
extends to 4” NPS for both the liquid flush and for the air or
gas blow-down. The reason for that is the volume of liquid
or gas required to achieve the necessary velocity through the
larger pipe sizes is quite significant.
As an example a 6” NPS pipeline would require
approximately 900 to 1000 GPM, depending on wall
thickness of the pipe, to achieve a velocity of 10 FPS. This
gets a little cumbersome and costly. That is unless you have
pumps or compressors in place that can achieve the
necessary flow rate.
The alternative for liquid flushing the larger pipe sizes
other than using source line pressure or a pump is to perform
a fill-and-dump. In this process the pipe system is
completely filled with liquid and then drained through a full
line size, quick opening valve.
In doing this there has to be enough static head to
generate sufficient force and velocity to achieve essentially
the same result as the pumped or line pressure liquid.
Cleaning Category C-2 is a three-step process by which
the piping system is initially flushed out with a liquid to
remove most of the loose debris. This is followed by the
circulation of a cleaning solution, which is then followed by
a final flush of water.
Cleaning solutions are, in many cases, proprietary
detergent or acid-based solutions each blended for specific
uses. Detergent-based solutions are generally used for
removing dirt, cutting oils and grease. Acid-based solutions
are used to remove the same contaminants as the detergent-
base plus weld discoloration and residue. The acid based
solution also passivates the pipe wall.
As defined earlier, passivation provides a protective
oxide barrier against corrosion. The acids used in some
cleaning solutions for ferrous and copper materials leave
behind a passivated interior pipe surface as a result of the
cleaning process. In utility water services such as tower
water, chilled water, etc., this barrier against corrosion is
maintained with corrosion inhibitors that are injected into
the fluid stream on an ongoing basis.
And keep in mind that when I talk about passivated
surfaces this is a natural occurrence with metals in an
oxygen environment. The acid merely initiates and speeds
up the process.
When using stainless alloys, usually 316L, in hygienic
water services such as Water For Injection (WFI), Purified
Water, Deionized (DI) Water and in some cases Soft Water,
passivation is a final intended step in the preparation for
service of these pipelines.
Passivation is also a periodic ongoing preventative
maintenance procedure. To explain: High purity water is
very corrosive and attacks any free iron found on the surface
of stainless pipe. Free iron has a tendency to come out of
solution when material is cold worked, as in bending or
forming pipe without the benefit of heat. It also occurs with
the threading of alloy bolts, which are solution annealed
(heat treated) after threading. Passivation removes this free
iron while also accelerating, in the presence of O2, the
oxidation rate of the stainless steel providing a chromium
rich oxide corrosion barrier as defined above.
Over time (and this is one hypothetical thought on the
subject), this very thin corrosion barrier tends to get depleted
or worn off, particularly at high impingement areas of the
piping system (elbows, tees, pump casings, etc.). Once the
passive layer wears through any free iron exposed to the
high purity water will oxidize, or rust. This will show up as
surface rouge.
Rouging is an unwanted surface discoloration which is
periodically removed by means of a derouging process. This
is an operational, as-needed chemical cleaning process that
will remove all or most of the rouge and also re-passivate the
internal pipe surface.
9
Discussions and research on the topic of rouging
continues. This is a subject that has more questions than
answers at the present time. Currently the ASME-BPE is
looking into this issue. One of the questions to be answered
is whether or not rouge is actually detrimental to product
streams.
Cleaning Category C-3 is a two-step cleaning process
that uses a detergent or acid based solution to clean the pipe
interior of any unwanted residue or debris. This is then
followed by a final flush of water.
Cleaning Category C-4 is a three or four-step process
generally used in hygienic service piping. In most cases,
simply due to the clean fabrication approach used in
hygienic pipe fabrication, only a water flush with Deionized
(DI) quality water or better would be necessary for cleaning
followed by passivation of the piping system, then a final
flush of water.
There are variations to each of these primary cleaning
functions and it would be in an Owner’s best interest to
define these requirements, by fluid service, in advance of the
work to be done.
LEAK TESTING
Pressure testing is a misnomer that is quite often used
when referring to leak testing of piping systems. And as long
as all parties understand what is meant by that, then that’s
fine. However, in a true sense a pressure test is a test you
perform on a relief valve to test its set point pressure. The
intent, when pressure testing a relief valve, is not to check
for leaks, but to test the pressure set point of the valve by
gradually adding pressure to the relief valve until it lifts the
valve off of the seat.
A leak test, on the other hand, is performed to check the
sealing integrity of a piping system by applying internal
pressure to a pre-determined limit, based on design
conditions, then checking joints and component seals for
leaks. It is not intended that the MAWP of a piping system
be verified or validated.
Before discussing the various types of leak tests and
leak test procedures I would like to briefly talk about
controlling and tracking this activity.
Cleaning and testing, like many aspects of a project,
should be a controlled process. Meaning, there should be a
formal method of documenting and tracking this activity as
the Contractor proceeds through the leak testing process..
In documenting the leak testing activity there are certain
forms that will be needed. They consist of the following:
1. A dedicated set of P&ID’s to identify the limits
and number the test circuits;
2. A form to record components that were either
installed or removed prior to testing;
3. A checklist form for field supervision to ensure
that each step of the test process is
accomplished; and
4. Leak test data forms
The two sets of documents, from those listed above, that
need to be retained are the P&ID’s (#1) and the Leak Test
Data Forms (#4). The other two sets of forms are procedural
checklists.
The Leak Test Data forms should contain key data such
as:
1. Test circuit number
2. P&ID number(s)
3. Date of test
4. Project name and/or number
5. Location within facility
6. Line number(s)
7. Design pressure
8. Test pressure
9. Test fluid
10. Test fluid temperature
11. Time (military) recorded test begins
12. Pressure at start of test
13. Time (military) recorded test ends
14. Pressure at end of test
15. Total elapsed time of test
16. Total pressure differential (plus or minus) from
beginning to end of test period
17. Comment section (indicate if leaks were found and
system was repaired and retested or if system
passed)
18. Signatures & dates
Also make certain that the testing contractor has current
calibration logs of their test instruments, such as pressure
gages.
To continue with the leak testing, ASME B31.3 defines
five primary leak tests as follows:
Initial Service Leak Test: This applies only to those
fluid services meeting the criteria as defined under ASME
B31.3 Category D fluid service. This includes fluids in
which the following apply:
(1) the fluid handled is nonflammable, nontoxic,
and not damaging to human tissue;
(2) the design gage pressure does not exceed 1035
kPA (150 psi); and
(3) the design temperature is from -29°C (-20°F)
through 186°C (366°F).
The Initial Service leak test is a process by which the
test fluid is the fluid that is to be used in the intended piping
system at operating pressure and temperature. It is
accomplished by connecting to the fluid source with a
10
valved connection and then gradually opening the source
valve and filling the system. In liquid systems air is purged
during the fill cycle through high point vents. A rolling
examination of all joints is continually performed during the
fill cycle and for a period of time after the system is
completely filled and is under line pressure.
In a situation in which the distribution of the pipeline
that is being tested has distribution on multiple floors of a
facility there will be pressure differentials between the floors
due to static head differences. This will occur in operation
and is acceptable under initial service test conditions.
The test pressure achieved for initial service testing
pressure is what it is. Meaning that what you achieve in the
test is what it will be in operation. The only difference is that
the flowing fluid during operation will incur an amount of
pressure drop that will not be present during the static test.
Hydrostatic leak test: This is the most commonly used
leak test and is performed by using a liquid, normally water,
and in some cases with additives to prevent freezing, under a
calculated pressure.
(eq. 1)
(eq. 1.1)
Eq. 1 represents the equation for that calculated
pressure. However, as long as the metal temperature of ST
remains below the temperature at which the allowable stress
value for ST begins to diminish and the allowable stress
value of S and ST are equal then ST and S cancel each other
leaving the simpler eq. 2:
(eq. 2)
Unlike initial service testing, pressure variations due to
static head differences in elevation have to be
accommodated in hydrostatic testing. What I mean by that is
the calculated test pressure is the minimum pressure required
for the system. When hydrostatically testing a multi-floor
system the minimum calculated test pressure shall be
realized at the highest point. This is not stated, but is inferred
in B31.3.
Pneumatic leak test: This test is performed using air or a
preferred inert gas. This is a relatively easy test to perform
simply from a preparation and cleanup standpoint. However,
this test has a hazardous potential because of the stored
energy in the pressurized gas. And for that reason alone it
should be used very selectively.
When pneumatic testing is performed it must be done
under a strictly controlled procedure with on-site supervision
in addition to coordination with all other crafts and
personnel in the test area.
(eq. 3)
(eq. 4)
(eq. 5)
The test pressure for pneumatic leak testing under B31.3
is calculated using eq. 3, for B31.9 it is calculated using eq.
4, and for B31.1 it is calculated using eq. 5.
One misconception I need to address here with
pneumatic leak testing is in its procedure, as described in
B1.3. There is a misconception that the test pressure should
be maintained while the joints are examined. This is not
correct. As B31.3 explains, pressure is increased gradually
until the test pressure is reached. At that point the test
pressure is held until piping strains equalize throughout the
system.
After allowing a sufficient amount of time for piping
strains to equalize the pressure is then reduced to the design
pressure (refer to article II for design pressure). While
holding design pressure all joints are examined for leaks. It
is not required that the examination take place while holding
test pressure.
There is more to the entire procedure that I did not
include here. Please refer to B31.3 or B31.1 for full details
on pneumatic leak testing.
Sensitive leak test: This leak test is performed when
there is a higher than normal potential for fluid leakage, such
as for hydrogen. I also recommend its use when a fluid is
classified as a Category M fluid service. B31.1 refers to this
test as Mass-Spectrometer and Halide Testing.
In B31.3 the process for sensitive leak testing is as
follows:
The test shall be in accordance with the gas and bubble
test method specified in the BPV Code, Section V, Article 10,
or by another method demonstrated to have equal sensitivity.
Sensitivity of the test shall be not less than 10-3
atm-ml/sec
under test conditions.
(a) The test pressure shall be at least the lesser of
105kPa (15 psi) gage, or 25% [of] the design pressure.
Where:
PT = Test Pressure, psi
P = Internal design gage pressure, psig
ST = Stress value at test temperature, psi (see B31.3 Table A-1)
S = Stress value at design temperature, psi (see B31.3 Table A-1
S
PSP T
T
5.1
PPT 5.1
PPT 1.1
PPT 4.1
PPtoPT 5.12.1
11
12)(K
UL
Dy
(b) The pressure shall be gradually increased until a
gage pressure the lesser of one-half the test pressure or 170
kPa (25 psi) gage is attained, at which time a preliminary
check shall be made. Then the pressure shall be gradually
increased in steps until the test pressure is reached, the
pressure being held long enough at each step to equalize
piping strains.
In testing fluid services that are extremely difficult to
seal against, or fluid services classified as a Category M
fluid service I would suggest the following in preparation for
the process described under B31.3: prior to performing the
sensitive leak test perform a low pressure (15 psig) test with
air or an inert gas using the bubble test method. Check every
mechanical joint for leakage.
After completing the preliminary low pressure
pneumatic test, purge all of the gas from the system using
helium. Once the system is thoroughly purged, and contains
no less than 98% helium, continue using helium to perform
the sensitive leak test with a helium mass spectrometer.
Helium is the trace gas used in this process and has a
molecule that is close to the size of the hydrogen molecule
making it nearly as difficult to seal against as hydrogen
without the volatility. Test each mechanical joint using the
mass-spectrometer to determine leak rate, if any.
Alternative leak test: In lieu of performing an actual
leak test, in which internal pressure is used, the alternative
leak test takes the examination and flexibility analysis
approach.
This test is conducted only when it is determined that
hydrostatic or pneumatic testing would be detrimental to the
piping system and/or the fluid intended for the piping
system, an inherent risk to personnel, or impractical to
achieve.
As an alternative to testing with internal pressure it is
acceptable to qualify a system through examination and
flexibility analysis. The process calls for the examination of
all groove welds, and includes longitudinal welds used in the
manufacture of pipe and fittings that have not been
previously tested hydrostatically or pneumatically. It
requires a 100% radiograph or ultrasonic examination of
those welds. Where applicable, the sensitive leak test shall
be used on any untested mechanical joints. This Alternative
leak test also requires a flexibility analysis as applicable.
Very briefly, a flexibility analysis verifies, on a
theoretical basis, that an installed piping system is within the
allowable stress range of the material and components under
design conditions if a system: (a) duplicates or replaces
without significant change, a system operating with a
successful service record; (b) can be judged adequate by
comparison with previously analyzed systems; and (c) is of
uniform size, has no more than two points of fixation, no
intermediate restraints, and falls within the limitations of
empirical equation (eq. 6).
(eq. 6)
Where:
D = outside diameter of pipe. in. (mm)
y = resultant of total displacement strains to be
absorbed by piping system, in. (mm)
L = developed length of piping between anchors, in.
(mm)
U = anchor distance, straight line between anchors,
ft. (m)
K1 = 208,000 SA/Ea, (mm/m)2
= 30 SA/Ea, (in./ft.)2
SA = allowable displacement stress range per
equation (1a) of ASME B31.3, ksi (MPa)
Ea = reference modulus of elasticity at 70°F
(21°C), ksi (MPa)
One example in which an alternative leak test might be
used is in making a branch tie-in to an existing, in-service
line using a saddle with an o-let branch fitting with a weld
neck flange welded to that and a valve mounted to the
flange. Within temperature limitations, the fillet weld used
to weld the saddle to the existing pipe can be examined
using the dye penetrant or magnetic particle method. The
circumferential butt or groove weld used in welding the weld
neck and the o-let fitting together should be radiographically
or ultrasonically examined. And the flange joint connecting
the valve should have the torque of each bolt checked after
visually ensuring correct type and placement of the gasket.
There are circumstances, regarding the tie-in scenario
we just discussed for alternative leak testing, in which a
hydrostatic or pneumatic test can be used. It depends on
what the fluid service is in the existing pipeline. If it is a
fluid service that can be considered a Category D fluid
service then it is quite possible that a hydrostatic or
pneumatic leak test can be performed on the described tie-in.
By capping the valve with a blind flange modified to
include a test rig of valves, nipples and hose connectors, you
can perform a leak test rather than an alternative leak test.
As mentioned this does depend on the existing service fluid.
If the existing fluid service is steam or a cryogenic fluid then
you might want to consider the alternative leak test.
Cleaning and Leak Testing Procedures
As you can see by equations eq. 1 through eq. 5 above,
the leak test pressure, except for initial service testing, is
based on design pressure and design temperature. In Article
2 we described design pressure and temperature. What we
will do here is apply that understanding and describe a few
general procedures for cleaning and testing.
12
As in all other project functions control and
documentation is a key element in the cleaning and testing
of piping systems. It does, however, need to be handled in a
manner that is dictated by the type of project. Meaning that
you don’t want to bury yourself in unwarranted paperwork
and place an unneeded burden on the contractor when it isn’t
necessary.
Building a commercial or institutional type facility will
not require the same level of documentation and stringent
controls that an industrial type facility would require. But
even within the industrial sector there are varying degrees of
required testing and documentation.
To begin with, documentation requirements in industry
standards are simplistic and somewhat generalized, as is
apparent in ASME B31.3, which states in Para. 345.2.7:
Records shall be made of each piping system during the
testing, including:
(a) date of test
(b) identification of piping system tested
(c) test fluid
(d) test pressure
(e) certification of results by examiner
These records need not be retained after completion of
the test if a certification by the inspector that the piping has
satisfactorily passed pressure testing as required by this
Code is retained.
ASME B31.3 goes on to state, in Para. 346.3:
Unless otherwise specified by the engineering design,
the following records shall be retained for at least 5 years
after the record is generated for the project:
(a) examination procedures; and
(b) examination personnel qualifications.
Standards, that cover such a broad array of industrial
manufacturing, do not, as a rule, attempt to get too specific
in some of their requirements. Beyond the essential
requirements, such as those indicated above, the Owner,
engineer or contractor has to assume responsibility and
know-how for providing more specific and proprietary
requirements for a particular project specific to the particular
needs of the Owner. The following will help, to some extent,
fill that gap.
Cleaning Procedures
This section will describe some fundamental cleaning
procedures as they might appear in a specification or
guideline, and this includes the leak test procedures that
follow. This will give you some idea as to what you might
consider developing for your own set of specifications.
Assuming that if your company repeatedly executes projects
you will have cleaning and testing guidelines, in some form,
prepared for your contractor. If not you may not get what
you expect. It’s better to give some forethought to these
activities rather than be surprised at the results.
Once a menu of these cleaning and testing procedures
are developed, using pre-assigned symbols, much as those
given in the following, they can then be specified in the line
list with the respective fluid services as you require. In this
manner there is no second guessing during construction.
Each piping circuit is assigned a specific clean and test
protocol in advance.
Many pre-developed procedures I have seen over the
years, those developed by Owners in particular, have been
very simplistic, and typically out of date. This is an indicator
to most contractors that the Owners Rep will most likely not
attempt to enforce them. The contractor, in making that
assumption, may simply ignore them and perform their own
procedures.
What your procedural guidelines should do is be explicit
enough and current to the point where the contractors know
that someone has given some thought as to how they want
that work accomplished. Making it far more likely they (the
contractors) will execute your procedure instead of their’s.
It is certainly acceptable to accommodate suggestions to
a procedure from a contractor when it doesn’t compromise
the intent of the Owner’s requirements and improves the
efficiency of the contractor. If a submitted alternate
procedure does not compromise the intent of the Owner it is
recommended that they be accepted. This will allow the
Owner to see if that efficiency is really there. With that in
mind let’s create a couple of general cleaning procedures.
A general practice in the flushing and cleaning process,
also indicated in leak testing, is the evacuation of air when
using liquids. Always provide high point vents for
evacuating air during the fill cycle and low point drains for
clearing out all of the liquid when the process is complete.
Using the same symbology indicated in Table 3-2 these
cleaning procedures will be categorized as follows:
Category C-1: Flush or Blow Down only (water, air or inert
gas)
C-1.1 These systems shall be flushed with the fluid that the
system is intended for. There shall be no hydrostatic
or pneumatic leak test. An Initial Service leak test will
be performed. Refer to test Category T-1.
a. Connect system to its permanent supply line.
Include a permanent block valve at the supply line
connection. All outlets shall have temporary hoses
run to drain. Do not flush through coils, plates,
strainer or filter elements.
13
b. Using supply line pressure, flush system through all
outlets until water is clear and free of any debris at
all outlet points. Flush a quantity of fluid through
each branch not less than three times that contained
in the system. Use Table 3-6 to estimate volume of
liquid in the system.
c. These systems are required only to undergo an
Initial Service leak test. During the flushing
procedure, and as the system is placed into service,
all joints shall be checked for leaks.
d. Any leaks discovered during the flushing process,
or during the process of placing the system into
service, will require the system to be drained and
repaired. After which the process will start over
with step 2.
C-1.2 These systems shall be flushed clean with Potable
Water.
a. Connect a flush/test manifold at a designated inlet
to the system, and a temporary hose or pipe on the
designated outlet(s) of the system.
b. Route temporary hose or pipe from potable water
supply, approved by Owner, and connect to
flush/test manifold. Route outlet hose or pipe to
sewer, or as directed by Owner rep. Secure end of
outlet.
c. Using a Once through procedure (not a re-
circulation), and the rate of flow in Table 3-4,
perform an initial flush through the system with a
quantity of potable water not less than three times
that contained in the system. Use Table 3-6 to
estimate volume of liquid in the system. Discharge
to sewer, or as directed by Owner rep.
d. After the initial flush, insert a conical strainer into
a spool piece located between the discharge of the
piping system and the outlet hose. Perform a second
flush with a volume of potable water not less than
that contained in the system.
e. After the second flush (step 4), pull the strainer
and check for debris; if debris is found repeat step 3.
If no debris is found the system is ready for leak
testing.
Category C2: Flush then clean with cleaning solution,
followed by a neutralization rinse. Because of the
thoroughness of the flush, clean and rinse process there
should be no need to check for transient debris, only for
neutralization. However, if circumstances dictate otherwise
then a final check for debris may be warranted.
C-2.1 These systems shall be pre-flushed with potable water,
cleaned with (indicate cleaning agent) then a
rinse/neutralization followed by leak testing with
potable water. If it is determined that the system will
be installed and tested progressively in segments, the
sequence of cleaning and testing can be altered to
follow the segmented installation. Thereby leak
testing segments of a piping system as they are
installed without cleaning. The entire system would
then cleaned once installed and tested.
a. Hook up flush/test manifold at a designated
temporary inlet to the system between the
circulating pump discharge and the system inlet.
Install a temporary hose or pipe on the designated
outlet(s) of the system.
b. Route temporary hose or pipe from potable water
supply, approved by Owner, and connect to
flush/test manifold. Route outlet hose or pipe to
sewer, or as directed by Owner’s Rep.
c. Close valve between the circulating pump (if no
valve included in the system design insert a line-
blind or install a blind flange with a drain valve)
discharge and flush/test rig. Open valve between
flush/test manifold and piping system.
d. Using the once through procedure (meaning the
cleaning fluid is not re-circulated), and the rate of
flow in Table 3-4, perform an initial flush through
the system, by-passing the circulation pump, with a
quantity of potable water equal to not less than three
times that contained in the system. Use Table 3-6 to
estimate volume of liquid in the system.
(Note: During the water flush check the system for
leaks. Verify no leaks prior to introducing chemical
cleaning solution to the piping system.)
Table 3-6 – Volume of Water Per Lineal Foot of Pipe (gal.)
Pipe Sizes (inches)
Sch. 1/2 3/4 1 11/2 2 3 4 6 8 10 12 14 16 18 20 24
5s .021 .035 .058 .129 .207 .455 .771 1.68 ─ ─ ─ ─ ─ ─ ─ ─
20 ─ ─ ─ ─ ─ ─ ─ ─ 2.71 4.31 6.16 7.34 9.70 12.4 15.2 22.2
40 .016 .028 .045 .106 .176 .386 .664 1.51 2.61 4.11 5.84 9.22 9.22 14.5 14.5 ─
80 .012 .023 .037 .093 .154 .345 .60 1.36 ─ ─ ─ ─ ─ ─ ─ ─
14
e. Discharge to sewer, or as directed by Owner’s
Rep.
f. After completing the initial flush, drain remaining
water in the system. Or, retain water if cleaning
chemicals will be added to the circulating water.
g. Configure valves and hoses to circulate through
pump. Connect head tank, or other source
containing cleaning agent, to connection provided
on circulation loop.
h. Fill the system with the pre-measured (indicate
preferred cleaning agent and mixing ratio or % by
volume) and circulate through the system for 48
hours. To minimize corrosion, if anticipated,
circulate cleaning agent at a low velocity rate
prescribed by the cleaning agent manufacturer.
i. Drain cleaning agent to sewer or containment, as
directed by Owner.
j. Reconnect as in step #1 for the once through
flush/neutralization, and flush system with potable
water using a quantity not less than three times that
of the system volume. Since the (name cleaning
agent) solution has a neutral pH the rinse water will
have to be visually examined for clarity. Rinse until
clear. The rinse must be started in as short as
quickly after the cleaning cycle as possible. If
cleaning residue is allowed to dry on the interior
pipe wall, it will be more difficult to remove by
simply flushing. The final rinse and neutralization
must be accomplished before any possible residue
has time to dry.
k. Test pH for neutralization. Once neutralization is
achieved proceed to step #12.
l. Remove pump and temporary circulation loop
then configure the system for leak testing. This may
include removal of some components, insertion of
line-blinds, installation of temporary spools pieces,
etc.
Those three examples should provide an idea as to the
kind of dialog that needs to be created in providing guidance
and direction to the contractor responsible for the work.
And, as I stated earlier, these procedures, for the most part,
are flexible enough to accommodate suggested
modifications from the contractor.
Leak Test Procedures
As in the cleaning procedures we will keep this general,
but provide enough specifics for you to develop leak testing
procedures that will suit your company’s own particular
needs.
In Article 1 I stated the B31.3 definition for Category D
fluid services. I then indicated that while Category D fluid
services qualified for initial service leak testing there are
caveats that should be considered.
Again, this is a situation in which ASME provides
some flexibility in testing by lowering the bar on
requirements where there is reduced risk in failure.
Provided, that if failure should occur the results would not
cause catastrophic damage to property or irreparable harm to
personnel.
The Owner’s responsibility, for any fluid service
selected for initial service leak testing lies in determining
what fluid services to place into each of the fluid service
Categories. Those Categories being: Normal, Category D,
Category M, and High Pressure.
Acids, caustics, volatile chemicals and petroleum
products are usually easy to identify as those not qualifying
as a Category D fluid service. Cooling tower water, chilled
water, air, and nitrogen are all easy to identify as qualifyiers
for Category D fluid services. The fluid services that fall
within the acceptable Category D guidelines, but still have
the potential for being hazardous to personnel are not so
straight forward.
Using water as an example, at ambient conditions water
will simply make you wet if you get dripped or sprayed on.
Once the temperature of water exceeds 140°F (60°C), by
OSHA standards, it starts to become detrimental to
personnel upon contact. At this point the range of human
tolerance becomes a factor. However, as the temperature
continues to elevate it eventually moves into a range that
increasing becomes scalding upon human contact and human
tolerance is no longer a factor because it is now hazardous
and the decision is made for you.
Before continuing I need to be clear on the above
subject matter. The 140ºF temperature mentioned above is
with respect to simply coming in contact with an object at
that temperature. Brief contact at that temperature would
not be detrimental. In various litigation related to scalding it
has been determined that an approximate one-second
exposure to 160°F water will result in third degree burns.
An approximate half-minute exposure to 130°F water will
result in third degree burns. And an approximate ten minute
exposure to 120°F water can result in third degree burns.
With the maximum temperature limit of 366°F
(185.5°C) for Category D fluid services what the Owner
needs to consider here are three factors: within that range of
140°F (60°C), the temperature at which discomfort begins to
set in, to 366°F (185.5°C), the upper limit of Category D
fluids, what do we consider hazardous; what is the level of
15
opportunity for risk to personnel; and what is the level of
assured integrity of the installation.
What I mean by assured integrity is this: if there are
procedures and protocols in place that require, validate and
document third-party inspection of all pipe fabrication,
installation and testing, then there is a high degree of assured
integrity in the system. If some or all of these requirements
are not in place then there is no assured integrity.
All three of these factors: temperature, risk of contact,
and assured integrity, have to be considered together to
arrive at a reasonable determination for borderline Category
D fluid services. If, for instance, a fluid service is hot
enough to be considered hazardous, but is in an area of a
facility that sees very little personnel activity then the fluid
service could still be considered as a Category D fluid
service.
One factor I have not included here is the degree of
relative importance of a fluid service, or in other words, if a
system failed how big of a disruption would it cause in plant
operation, and how does that factor into this process.
As an example, if a safety shower water system has to
be shut down for leak repair the down-time to make the
repairs has little impact on plant operations. This system
would therefore be of relative low importance and not a
factor in this evaluation process.
If on the other hand a chilled water system has to be
shut down for leak repair to a main header, this could have a
significant impact to operations and production. This could
translate into lost production and could be considered a high
degree of importance.
You could also extend this logic a bit further by
assigning normal fluid service status to the primary headers
of a chilled water system and assigning Category D status to
the secondary distribution branches then leak test
accordingly. You need to be cautious in considering this. By
applying different Category significance to the same piping
system it could cause more confusion than it is worth. In
other words it may be more value added to simply default to
the more conservative Category of Normal.
Continuing; if we can consider that there is a high
assured integrity value for these piping systems there are two
remaining factors to be considered. The first would be:
within the above indicated temperature range at what
temperature should a fluid be considered hazardous; and
secondly, how probable is it that personnel could be in the
vicinity of a leak, should one occur.
For our purpose here let us determine that any fluid
160°F (71°C) and above is hazardous upon contact with
human skin. If the fluid you are considering is within this
temperature range then it has the potential of being
considered a normal fluid, as defined in B31.3, pending its
location as listed in Table 3-7.
Table 3-7 – Areas Under Consideration For Cat. D
Group Description Yes No
1 Personnel Occupied Space √
2 Corridor Frequented by
Personnel
√
3 Sensitive Equipment (MCC,
Control Room, etc.) √
4 Corridor Infrequently Used by
Personnel √
5 Maintenance & Operations
Personnel Only Access √
As an example, if you have a fluid that is operating at
195°F (90.6°C) it would be considered hazardous in this
evaluation. But, if the system is located in a Group 5 area
(ref. Table 3-7) it could still qualify as a Category D fluid
service.
After the above exercise in evaluating a fluid service we
can now continue with a few examples of leak test
procedures. Using the same symbology indicated in Table 3-
3 these leak test procedures will be categorized as follows:
Category T-1: Initial Service Leak Test
T-1.1 This Category covers liquid piping systems
categorized by ASME B31.3 as Category D Fluid
service and will require Initial Service Leak Testing
only.
1. If the system is not placed into service or tested
immediately after flushing and cleaning, and has set
idle for an unspecified period of time it shall require
a preliminary pneumatic test at the discretion of the
Owner. In doing so, air shall be supplied to the
system to a pressure of 10 psig and held there for 15
minutes to ensure that joints and components have
not been tampered with, and that the system is still
intact. After this preliminary pressure check
proceed.
2. After completion of the flushing and cleaning
process, connect the system, if not already
connected, to its permanent supply source and to all
of its terminal points. Open the block valve at the
supply line and gradually feed the liquid into the
system.
3. Start and stop the fill process to allow proper high
point venting to be accomplished. Hold pressure to
its minimum until the system is completely filled
and vented.
4. Once it is determined that the system has been filled
and vented properly, gradually increase pressure
16
until 50% of operating pressure is reached. Hold
that pressure for approximately 2 minutes to allow
piping strains to equalize. Continue to supply the
system gradually until full operating pressure is
achieved.
5. During the process of filling the system, check all
joints for leaks. Should leaks be found at any time
during this process drain the system, repair leak(s)
and begin again with step 1. (Caveat: Should the
leak be no more than a drip every minute or two on
average at a flange joint, it could require simply
checking the torque on the bolts without draining
the entire system. If someone forgot to fully tighten
the bolts then do so now. If it happens to be a
threaded joint you may still need to drain the
system, disassemble the joint, clean the threads, add
new sealant and reconnect the joint before
continuing.)
6. Record test results and fill in all required fields on
the leak test form.
T-1.2.This Category covers pneumatic piping systems
categorized by ASME B31.3 as Category D Fluid
service and will require Initial Service Leak Testing.
1. After completion of the blow-down process, the
system shall be connected to its permanent supply
source, if not already done so, and to all of its
terminal points. Open the block-valve at the supply
line and gradually feed the gas into the system.
2. Increase the pressure to a point equal to the lesser of
one-half the operating pressure or 25 psig. Make a
preliminary check of all joints by sound or bubble
test. If leaks are found release pressure, repair
leak(s) and begin again with step 1. If no leaks are
identified continue to step 3.
3. Continue to increase pressure in 25 psi increments,
holding that pressure momentarily (approximately 2
minutes) after each increase to allow piping strains
to equalize, until the operating pressure is reached.
4. Check for leaks by sound and/or bubble test. If leaks
are found release pressure, repair leak(s) and begin
again with step 2. If no leaks are found the system is
ready for service.
5. Record test results and fill in all required fields on
the leak test form.
Category T-3.1: Hydrostatic Leak Test
T-3.1.This Category covers liquid piping systems
categorized by ASME B31.3 as Normal Fluid service.
1. If the system is not placed into service or tested
immediately after flushing and cleaning, and has set
idle for an unspecified period of time it shall require
a preliminary pneumatic test at the discretion of the
Owner. In doing so, air shall be supplied to the
system to a pressure of 10 psig and held there for 15
minutes to ensure that joints and components have
not been tampered with, and that the system is still
intact. After this preliminary pressure check
proceed.
2. After completion of the flushing and cleaning
process, with the flush/test manifold still in place
and the temporary potable water supply still
connected (reconnect if necessary), open the block
valve at the supply line and complete filling the
system with potable water.
3. Start and stop the fill process to allow proper high
point venting to be accomplished. Hold pressure to
its minimum until the system is completely filled
and vented.
4. Once it is determined that the system has been filled
and vented properly, gradually increase pressure
until 50% of the test pressure is reached. Hold that
pressure for approximately 2 minutes to allow
piping strains to equalize. Continue to supply the
system gradually until test pressure is achieved.
5. During the process of filling the system, and
increasing pressure to 50% of the test pressure,
check all joints for leaks. Should any leaks be found
drain system, repair leak(s) and begin again with
step 1.
6. Once the test pressure has been achieved, hold it for
a minimum of 30 minutes or until all joints have
been checked for leaks. This includes valve and
equipment seals and packing.
7. If leaks are found evacuate system as required,
repair and repeat from step 2. If no leaks are found,
evacuate system and replace all items temporarily
removed.
8. Record all data and activities on leak test forms.
Those three examples should provide an idea as to the
kind of guideline that needs to be created in providing
direction to the contractor responsible for the work.
For leak testing to be successful on your project, careful
preparation is key. This preparation starts with gathering
information on test pressures, test fluids, and the types of
tests that will be required. The most convenient place for this
information to reside is the piping line list or piping system
list.
17
A piping line list and piping system list achieve the
same purpose only to different degrees of detail. On some
projects it may be more practical to compile the information
by entire service fluid systems. Other projects may require a
more detailed approach by listing each to and from line
along with the particular data for each line.
The line list itself is an excellent control document that
might include the following for each line item:
1. Line size
2. Fluid
3. Nominal material of construction
4. Pipe Spec
5. Insulation spec
6. P&ID
7. Line sequence number
8. from and to information
9. Pipe code
10. Fluid Service Category
11. Heat Tracing
12. Operating Pressure
13. Design Pressure
14. Operating Temperature
15. Design Temperature
16. Type of Cleaning
17. Test Pressure
18. Test Fluid
19. Type of Test
Developing this type of information on a single form
provides everyone involved with the basic information
needed for each line. Having access to this line-by-line
information in such a concise well organized manner
reduces guess-work and errors during testing.
Test results, documented on the test data forms, will be
maintained under separate cover. Together the line list
provides the required information on each line or system and
the test data forms provide signed verification of the actual
test data of the test circuits that make up each line or system.
VALIDATION
The process of Validation has been around for longer
than the 40 plus years I have been in this business. You may
know it by its less formal namesakes walk-down and
checkout. Compared to validation, walk-down and checkout
procedures are not nearly as complex, stringent, or all
inclusive.
Validation is actually a subset activity under the
umbrella of Commissioning and Qualification (C&Q). It is
derived from the need to authenticate and document
specifically defined requirements for a project and stems
indirectly from, and in response to, the Code of Federal
Regulation 29CFR Titles 210 and 211 current Good
Manufacturing Practice (cGMP) and FDA requirements.
These CFR Titles and FDA requirements drove the need to
demonstrate or prove compliance.
These requirements can cover everything from
verification of examination and inspection, documentation of
materials used, software functionality and repeatability to
welder qualification, welding machine qualification, etc.
The cGMP requirements under 29CFR Titles 210 & 211
are a vague predecessor of what validation has become, and
continues to become. From these basic governmental
outlines companies, and the pharmaceutical industry as a
whole, have increasingly provided improved interpretation
of these guidelines to meet many industry imposed, as well
as self-imposed requirements.
To a lesser extent, industrial projects outside the
pharmaceutical, food & drug, and semi-conductor industries,
industries not prone to require such in-depth scrutiny, could
benefit from adopting some of the essential elements of
validation. Elements such as: material verification, leak test
records, welder and welding operator qualification records,
etc.
At face value this exercise would provide an assurance
that the fabricating/installing contractor is fulfilling their
contractual obligation. The added benefit is that in knowing
that this degree of scrutiny will take place the contractor will
themselves take extra pain to minimize the possibility of any
rejects.
And I am not inferring that all contractors are out to get
by with as little as they can. Just the opposite is actually true.
Most contractors qualified to perform at this level of work
are in it to perform well and to meet their obligations. Most
will already have their own verification procedure in place.
The bottom line is that the Owner is still responsible for
the end result. No one wants to head for the litigation table at
the end of a project. And the best way to avoid that is for the
Owner to be proactive in developing their requirements prior
to initiating a project. This allows the spec writers and
reviewers the benefit of having time to consider just what
those requirements are and how they should be defined
without the time pressures imposed when this activity is
project driven.
Performing this kind of activity while in the heat of a
project schedule tends to force quick agreement to
specifications and requirements written by parties other than
those with the Owner’s best interest at heart.
Validating a piping system to ensure compliance and
acceptability is always beneficial and money well spent.
Wrapping Up
18
Before closing out this last of three articles there are just
a couple of things I would like to touch on. We had
discussed industry Standards earlier and how they are
selected and applied on a project. What I didn’t cover is the
fact that most projects will actually have a need to comply
with multiple industry Standards.
In a large grass-roots pharmaceutical project you may
need to include industry compliance Standards for much of
the underground utility piping, ASME B31.1 for boiler
external piping (if not included with packaged boilers),
ASME B31.3 for chemical and utility piping throughout the
facility, and ASME-BPE for any hygienic piping
requirements.
These and other Standards, thanks in large part to the
cooperation of the standards developers and ANSI, work
hand-in-hand with one another by referencing each other
where necessary. These Standards committees have enough
work to do within their defined scope of work without
inadvertently duplicating work done by other Standards
organizations.
An integrated set of American National Standards is the
reason that, when used appropriately, these Standards can be
used as needed on a project without fear of conflict between
those Standards.
One thing that should be understood with industry
Standards is the fact that they will always be in a state of
flux; always changing. And this is a good thing. These are
changes that reflect updating to a new understanding,
expanded clarification on the various sections that make up a
Standard, staying abreast of technology, and simply building
the knowledge base of the Standard.
As an example, two new Parts are being added to the
seven Parts currently existing in ASME-BPE. There will be
a Metallic Materials of Construction Part MMOC, and a
Certification Part CR. This is all part of the ever-evolving
understanding of the needs of the industrial community and
improved clarification, through discussion and debate on
content.
Writing these articles was a form of informational triage
for me. There were definite piping topics I wanted to include
and others I would have preferred to include, but could leave
out without too much of an impact. And then there were the
extended discussions on some topics that ultimately had to
be sacrificed. This is why some topics were briefer than I
would have liked.
My attempt at covering such a wide range of discussion
on industrial piping was to provide a basic broad
understanding of some key points on this topic, not, as I said
earlier, to go into great detail on any specific topic.
I hope that in writing these articles I piqued enough
interest that some of you will dig deeper into this subject
matter to discover and learn some of the more finite points
of what we discussed here. I also hope these articles
provided enough basic knowledge of piping for you to
recognize when there is more to a piping issue than what you
are being told.
Acknowledgement:
My deep appreciation again goes to Earl Lamson, senior
Project Manager with Eli Lilly and Company, for taking the
time to review each of these three articles. His comments
help make this article, and the others, better documents than
they otherwise would have been. He obliged me by applying
the same skill, intelligence and insight he brings to
everything he does. His comments kept me concise and on
target.
About the author:
W. M. (Bill) Huitt has been
involved in industrial piping
design, engineering and
construction since 1965.
Positions have included design
engineer, piping design
instructor, project engineer,
project supervisor, piping
department supervisor,
engineering manager and
president of W. M. Huitt Co. a
piping consulting firm founded
in 1987. His experience covers both the engineering and
construction fields and crosses industrial lines to include
petroleum refining, chemical, petrochemical,
pharmaceutical, pulp & paper, nuclear power, biofuel, and
coal gasification. He has written numerous specifications,
guidelines, papers, and magazine articles on the topic of pipe
design and engineering. Bill is a member of ISPE
(International Society of Pharmaceutical Engineers), CSI
(Construction Specifications Institute) and ASME
(American Society of Mechanical Engineers). He is a
member of three ASME-BPE subcommittees, several Task
Groups, an API Task Group, and sets on two corporate
specification review boards. He can be reached at:
W. M. Huitt Co.
P O Box 31154
St. Louis, MO 63131-0154
(314)966-8919
www.wmhuitt.com