Chemical Engineering August 2023 - 41

the piping to fire and the melting
point, degradation temperature,
loss of strength at elevated
temperature, and combustibility
of the piping material under
such exposure
* The susceptibility to brittle failure
or failure from thermal shock
of the piping material when
exposed to fire or to fire-fighting
measures, and possible hazards
from fragmentation of the material
in the event of failure
* The ability of thermal insulation
to protect piping against failure
under fire exposure (for example,
its stability,fire resistance,
and ability to remain in place
during a fire)
* The susceptibility of the piping
material to crevice corrosion
under backing rings, in threaded
joints, in socket welded
joints, and in other stagnant,
confined areas
* The possibility of adverse
electrolytic effects if the metal
is subject to contact with a dissimilar
metal
* The compatibility of lubricants or
sealants used on threads with
the fluid service
* The compatibility of packing,
seals, and O-rings with the
fluid service
* The compatibility of materials,
such as cements, solvents, solders,
and brazing materials, with
the fluid service
* The chilling effect of sudden
loss of pressure on highly
volatile fluids as a factor in determining
the lowest expected
service temperature
* The possibility of pipe support
failure resulting from exposure
to low temperatures (which
may embrittle the supports) or
high temperatures (which may
weaken them)
* The compatibility of materials,
including sealants, gaskets, lubricants,
and insulation, used in
strong oxidizer fluid service (for
example, oxygen or fluorine)
* The possibility of adverse effects
from microbiologically influenced
corrosion (MIC) or its remediation
And with regard to the selection
of material for systems that fall
under the rules for ASME B31.3
High Pressure piping, things become
much more complicated.
For a high-pressure system, you
will not only take into consideration
material compatibility with the fluid
service, but will also need to consider
the effect of high pressure,
we'll say, as an order of magnitude,
in excess of 1,000 psig, on the material
itself in conjunction with the
design temperature.
At higher pressures or elevated
temperatures, or both, you will
need to assess the risk to the selected
material for such concerns
as hydrogen embrittlement as well
as items of concern listed in ASME
B31.3, paragraph K302 Design Criteria
for high pressure piping. Those
concerns include the following:
* Tensile, compressive, flexural,
and shear strength at design
temperature
* Fatigue strength
* Design stress and its basis
* Ductility and toughness
* Possible deterioration of mechanical
properties in service
* Thermal properties
* Temperature limits
* Resistance to corrosion and
erosion
* Fabrication methods
* Examination and testing methods
* Hydrostatic test conditions
* Bore imperfections
And while the material selection
process, as discussed, pertains to a
piping system as an example, it can
also be applied to process vessels
and other equipment, with one glaring
exception. The rules for pressure
vessels are much broader and much
more specific and demanding than
the rules for piping. The dynamics
that have to be considered when
selecting material for equipment are
different, and the fabrication rules
are much different and varied than
they are for piping.
Material cost
The last thing to be considered will
be the installed cost of the selected
MoC. The installed cost is the last
thing to be considered because the
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AUGUST 2023
safety and integrity of a process system
is first and foremost in the selection
process. And once the selection
has been decided upon for compatibility,
safety and integrity, and you are
left with multiple materials, including
nonmetallic materials, it then comes
down to the installed cost.
Including the installed cost can
actually move the needle from a low
front-end cost for a material that
may be more costly to install to a
material that has a higher front-end
cost, but may be less costly to install.
So, when making that final decision
on which material to go with,
base it on the total installed cost,
not the base material alone.
The material selection process discussed
in this article is explained in
a rather straight-forward and simplified
manner, but the process itself,
and all that it entails, in all actuality
should be carried out by an individual
with years of experience in the CPI
- someone with a history of working
with the various materials and fluid
services used in this industry.
n
Edited by Gerald Ondrey
Author
William 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
(1070 Sarala Road, St. Louis, MO 63131-0154; Email:
wmhuitt@aol.com; Website: www.wmhuittco.com). His
experience covers both the engineering and construction
fields and crosses industry lines to include petroleum
refining, chemical, petrochemical, pharmaceutical, bioprocessing,
pulp-and-paper, nuclear power, biofuel and
coal gasification. He has written numerous specifications,
procedures on design and construction, guidelines, papers
and magazine articles on the topic of piping design
and engineering. Huitt has also written " Bioprocessing
Piping and Equipment Design - A Companion Guide for
the ASME BPE Standard, " published through the publishing
partnership of ASME Press and Wiley Publishing. He
is a past member of the International Society of Pharmaceutical
Engineers, the Construction Specifications Institute
and a current and active member of ASME. He is a
member of the B31.3 section committee, past Chair of
B31.3 Subgroup H on High Purity Piping, Vice Chair of
ASME BPE subcommittee on Certification, a member of
three other ASME- BPE subcommittees and is active on
several Task Groups. Huitt is also a member of the ASME
Board on Conformity Assessment for BPE Certification, a
member of the A13 Standards Committee for Standard
A13.1 Scheme for the Identification of Piping Systems, a
member of the API Task Groups for RP-2611 and RP1110.
He also authored the training program and provides
training to ASME consultants for auditing fitting
manufacturers who are applying for or renewing their
ASME BPE Certification.
41
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