Chemical Engineering October 2020 - 25

but the savings in time and effort in finding and correcting
needless leaks always outweighs these initial outlays.
Consider in-house or custom fabricating those things
you can't purchase. Machining specialty fittings, welding
two stock fittings together, or getting a custom component
manufactured is often feasible. The extra time spent
and cost are always recouped quickly through reduced
leak testing and locating and remedying leaks found.
Properly mount equipment. Make sure the mounting
provides adequate strength to resist the forces that will be
applied to it. How often have you seen tubing bent near
a cartridge filter that required a wrench to remove or a
valve that can be seen to move slightly when it is turned?
Substantial-looking brackets can flex in unplanned directions.
Often the support for the bracket is too flimsy and
flexes. Supporting pipe or tubing to other pipe or tubing is
a bad practice. While it can prevent sagging on long runs,
it provides little support to prevent leakage.
Pipe removable components properly. Consider how
you would assemble and disassemble any component
that needs maintenance or changing such as filters, purifiers
or traps. How do you remove instruments for calibration
or control valves to replace trims? Plan on how
you remove them without generating needless leaks.
Zero-clearance fittings are well worth the extra cost.
Flexible hoses and removable U bends often eliminate or
at least reduce needless leakage. This may require extra
space during the layout.
Isolate vibrating equipment with damping pads or
springs. Flexible connections to fixed systems, such as
compressors, pumps, vacuum pumps and mixers, are
important for all piping (Figure 7). Make sure the supporting
structure is stiff enough that it does not vibrate or flex
during operation. Make sure that any residual vibration is
dampened as much as possible. Do not anchor tubing
supports to the rotating equipment stand. That usually
just transmits the vibration even further.
Carefully design systems subject to temperature
changes. Wherever possible, avoid or minimize joints.
Instead, use welding, brazing or soldering to eliminate
these potential leak points. Utilize specialty fittings and
components with fewer joints. Use more leak-resistant
components like vacuum fittings. Consider packless
valves and similar " sealless " components. Avoid heat
tracing if possible and consider small heated enclosures
instead. These raise the temperature of all the internal
components at a similar rate and minimize leaks due to
uneven thermal stresses. Heated enclosures will, unfortunately,
still result in piping leaks upon cooling or other
temperature changes, but will avoid numerous routine
temperature differentials that are always produced by
heat-tracing systems. These differentials are certain to
increase the number of leaks. The use of heated enclosures
also allows modification, leak testing and maintenance
without insulation removal and replacement -
another cost savings.
Consider keeping the system at a constant temperature
when not in service. The extra expense associated
with doing so is often more than offset by a reduced
leak rate. Provide for gradual heat up or cool down -
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
the slower, the better. Automating the process to slowly
ramp up or down over time is often a good way to implement
this method. Allow for expansion and contraction,
even in shorter runs.
Is it possible to implement all of these suggestions all
the time on all your units? Sadly, in the real world, probably
not. You likely will not have enough space, money or
time to always do everything 100% correctly 100% of the
time. But by following these guidelines as much as possible,
you can make significant improvements in reducing
pipe leakage.
■
Edited by Scott Jenkins
Author
Richard Palluzi, PE, CSP, is founder and owner of Richard P.
Palluzi LLC (72 Summit Drive, Basking Ridge, NJ 07920; Email:
rpalluzi@verizon.net; Phone: 1-908-285-3782), a consultancy
for the pilot-plant and laboratory research community. Palluzi
provides consulting on all aspects of safety and design for pilot
plants, laboratories, research facilities and operations. He retired
as a distinguished engineering associate after 40 years at ExxonMobil
Research and Engineering, where he was involved in the
design, construction and support of pilot plants and laboratories
for ExxonMobil affiliates worldwide. He is the author of two
books, over 100 articles and 40 presentations. Palluzi was chair of the AIChE Pilot
Plant Committee, ExxonMobil's Pilot Plant and Laboratory Safety Standards Committee
and ExxonMobil's Safe Operation Team for its Clinton Facility. He is on the National Fire
Protection Association NFPA-45 Fire Protection for Laboratories Using Chemicals and
NFPA-55 Industrial and Medical Gases committees. Palluzi also teaches courses for
the University of Wisconsin's Department of Engineering Professional Development, as
well as provides customized training to the research community. He holds B.S.Ch.E.
and M.S.Ch.E. degrees from Stevens Institue of Technology in Hoboken, N.J.
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Chemical Engineering October 2020

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