Chemical Engineering October 2020 - 22

Cover Story
Leak Prevention in SmallBore
Piping and Tubing
Richard Palluzi
Richard P Palluzi LLC
IN BRIEF
COMMOM CAUSES OF
LEAKAGE
HEATING AND COOLING
STRESS AND TORQUE
CLEARANCE ISSUES
GUIDANCE TO MINIMIZE
LEAKAGE
L
eakage in pipes is an ongoing problem
in research and development
facilities across many sectors of the
chemical process industries (CPI),
such as petrochemicals, pharmaceuticals,
food and beverage and others. Leakage can
negatively affect operations in pilot plants
and laboratory units, and can affect a wide
range of laboratory equipment, analytical instruments
and testing equipment. Leaks are
costly and time-consuming to find, and often
are even more expensive to fix. Leaks result in
poor-quality data or invalid results, which can
require needless rework. Because leaks create
unnecessary downtime and program delays,
they drain stretched research resources.
Leakage is often ignored or accepted as a
" necessary evil. " It is common for scientists and
engineers to talk about getting a system " leak
tight " as if it is a one-time activity. Yet every system,
no matter how well designed or well maintained,
is almost certain to leak somewhere at
some time. Therefore, leak testing needs to be
a routine activity, not a one-time task. Simultaneously,
research personnel commonly think of
leaks as unfortunate, but inevitable occurrences,
like adverse weather conditions - " unfortunate,
but what can one do? " As a result of that mindset,
few efforts are made to prevent or minimize
the frequency of leaks.
Significantly better performance can be
achieved over time by (1) understanding the
common causes of leaks and (2) taking proactive
steps to reduce their frequency. This
article focuses on tubing and small-bore piping,
which are more common in research
and development.
Common causes of leakage
The following items constitute major causes
of leakage in piping systems.
Improper assembly. Pipe threads are often
under-tightened (Figure 1). Undersized
wrenches are often used because they are
handy or to get more clearance, but this results
in the need to exert more force in connecting
pipes, which is often not supplied.
22
Part 1
Improved understanding of the causes of piping leaks can reduce the frequency of leaks and
lead to significantly better performance over time
FIGURE 1. This photo shows a leaking pipe union, probably
resulting from being under tightened or forced together during
assembly
If upstream and downstream fittings are not
properly held, they may slip before the necessary
turns have been completed. In order
to achieve the desired alignment, fittings are
sometimes not tightened all the way. In order
to get fittings to match up, they are often
tightened insufficiently or forced into place.
The former results in a connection that is too
loose; the latter produces needless stresses,
eventually promoting leaks.
Poorly applied pipe sealant. Pipe sealant
is often seen as an area to reduce costs, so
inexpensive (and lower-quality) sealants may
be used, or sealant material may be applied
too lightly. Also, to save time, sealant may
be applied unevenly. Tapes are allowed to
bunch up due to poor assembly.
Badly threaded pipe fittings. Dies for
threading pipes are often used well past their
lifetimes, resulting in rounded threads that are
difficult to seal and are prone to leakage (Figure
2). When standard dies are used to thread
high-alloy pipe, they wear out quickly, usually
well before anyone realizes there is a problem.
Dies are sometimes not started carefully
enough, resulting in threads that are not
true and are more prone to leaks. Also, pipe
threads can be cut too short or too long to
make something fit an exact dimension.
Compression fittings are not tightened
properly. Pipe fittings are often tightened
by " feel " instead of by the number of turns.
Worse, many are deliberately under-tightCHEMICAL
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Chemical Engineering October 2020

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