MIL-HDBK-1003/11
12.3.1.3 Obtaining System Flexibility.
The following are available methods
for obtaining pipe system flexibility.
a) Offsets. Changing the pipe direction is the most economical
method of flexibility control when feasible, especially when used with ball
joints or grooved couplings.
b) Expansion Loops. Use expansion loops to limit pipe stresses
and to gain the necessary flexibility where changes in pipe direction cannot
be used or are insufficiently flexible. Pipe loops and offsets are
preferred over bellows or slip type expansion joints as they have high
reliability, are maintenance free, and require less anchorage and guiding.
c) Expansion Joints. Where space conditions are very restricted,
as in a trench, expansion joints of either the bellows or slip type are
applicable for axial movements, and the bellows type for some lateral
movement, when the bellows is designed for it. Both types may be used for
service pressures up to 250 lb/in2 (17.5 kg/cm2) for saturated steam.
Higher temperatures have a deteriorating effect on the packings of the slip
type. Also refer to NFGS-15711, Hot-Water Heating System, and NAVFAC DM
3.08. Maintaining pipe alignment is essential to the proper operation of
all types of expansion joints.
d) Pipe Sections with Ball Joints or Grooved Couplings. Where
pressure conditions permit, pipe sections with ball joints or grooved
connections may be used for three dimensional movements. Ball joins and
grooved couplings are self-restraining; their proper use can minimize the
need for anchors and pipe alignment guides. Proper selection of ball
coatings and seal materials will ensure lengthy low maintenance life.
Grooved coupling gaskets shall be of materials suitable for the fluids and
the temperatures involved.
12.4
Anchors and Supports.
12.4.1 Location. Locate anchors to control pipe line expansion and
contraction characteristics and to limit movements of branch takeoffs from a
main line. Careful consideration should be given to placement of anchors in
piping systems. Often a more flexible system and lower stresses will result
by the use of a minimum number of anchors, except in long straight lines.
Anchors must be provided to limit lateral motion of piping systems due to
seismic forces when installed inactive seismic zones.
12.4.1.1 Stops and Guides. Use stops or guides to direct movements away
from sensitive equipment such as pumps or turbines or to keep axial
alignments, particularly at expansion joints.
12.4.1.2 Rigid Hangers. Use roller or rod rigid hangers where vertical
movement is limited but not where they interfere with pipe flexibility.
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