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# RE: Pipe racks

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Pipe racks
• From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
• Date: Fri, 5 Oct 2001 15:18:15 -0400

```The forces on the structure due to piping depend on the details of the pipe
joints, the layout of the piping, internal pipe pressure, and on the
arrangement of the pipe supports. If the pipe joints are all restrained
(i.e. can transfer axial tension) and the supports do not restrain axial
movement, then there should be no need to resist static pipe thrust at
bends. But if there are unrestrained joints (e.g., pipe expansion joints,
couplings, etc), then the internal pressure will cause unbalanced thrust at
bends (or valves). (An easy way to look at pipe thrust due to internal
pressure is to draw force vectors along the axis of the pipe pointing
towards each bend. With restrained joints, the forces at each end of a
straight length of pipe will balance and will be resisted by tension in the
pipe wall. But if the pipe tension is broken due to an unrestrained joint,
then the force vector becomes unbalanced and must be externally restrained.)

Pipes with restrained joints should be provided with "pipe guides" to
laterally and/or vertically support the pipe periodically against movement
due to wind or seismic, but generally should not be axially restrained.
However, a single axial restraint near the center of a long run may be a
good idea to prevent longitudinal movement, but you should make sure the
bends can move freely to prevent restraint relative to the axial anchor.
Axial friction forces should be considered due to longitudinal thermal
movement or axial strain. Thermal movement causes very high forces if you
attempt to restrain axial movement but only frictional forces if the pipe is
free to expand axially. Friction coefficients for steel on steel can be 0.5
to 0.7; Teflon bearings can reduce friction to 0.04 to 0.10.

If you have structural beams between supports, I would recommend providing
slotted holes at one end support to allow thermal movement.

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