Chemical Engineering October 2020 - 27

Un-defl ected
shape
Bellows type
fl ex joints
Hot water heater
can reduce the reaction to a negligible
level. This can be achieved by mounting
the pump on spring mounts, on a
slide base or on threaded rods, allowing
them to bend.
Pipe guide
Exaggerated
defl ected
shape
Equipment nozzles
FIGURE 2. Expansion joints can reduce the loads
on equipment nozzles
pressure vessels also have load limits.
Loads due to gravity from smallbore
piping are generally not a major
concern, but loads induced by thermal
expansion can be enormous.
There are several strategies to reduce
these nozzle loads:
1. Create changes of direction in the
piping design to allow flexibility and
reduce forces
2. Consider designing cold spring
into the piping during installation
3. Evaluate the use of spring hangers
or supports to reduce thermal
and gravity loads across different
load cases
4. Consider flexible mounting of the
process
equipment.
Often,
high
forces can occur on a pump suction
- for example, when it is directly connected
to a tank with a straight piece
of pipe. While the thermal growth or
contraction of the pipe segment may
only be a small fraction of an inch, the
force required to resist the force generated
by the expansion can be tens
of thousands of pounds. Allowing the
pump to float by a 1/16th of an inch
5. Expansion/flex joints are an option
to reduce loads on equipment
nozzles. Unfortunately, they are often
incorrectly applied. Due to the pressure
thrust forces created by the
joint, it is very unlikely that a straight
bellows-type flex joint intended to
allow axial compression will resolve
forces on the pump suction example
above, unless the maximum pressure
that the system will experience
(which is typically test pressure) is
very low. These types of joints can
be very beneficial, however, in a lateral-displacement
configuration, as
shown in Figure 2.
Sometimes space constraints can
complicate supports near equipment,
and out-of-the-box solutions need
to be found. The images in Figure 3
show supports at pump suctions in a
hot-oil system, where the pipe needed
to be controlled both laterally and vertically,
but also needed freedom to grow
away from the pump suction.
Anchors, guides and slides
Anchors are critical components in
any large piping system, and are intended
to resist movement from all
forces in every direction. They establish
the boundaries and the control
conditions for all other pipe-stress
and support analysis. Anchors are
interesting in that they are not just
designed to support applied loads,
like hangers and guides. Instead,
they need to be evaluated for rigidity
or stiffness. For example, if an
anchor is attached to the top flange
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Un-stiffened
Support is intended
to be fl exible along
pump
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FIGURE 3. Pipe supports can allow lateral and vertical control, while also allowing freedom to grow
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OCTOBER 2020
ChemEng 2019.08 PP.indd 4
27
29.05.2019 14:34:33

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Chemical Engineering October 2020

Table of Contents for the Digital Edition of Chemical Engineering October 2020