Stress Analysis. For methods of analyzing stresses in piping
systems, use piping handbooks and publications of pipe and pipe fitting
manufactures. These manufacturers also supply calculation forms and charts.
Keep calculated pipe stresses under those allowed by ANSI B31.1.
Use NFGS-02694 for insulation
design for underground heat distribution piping. Use NFGS-02696 for above
grade steam, condensate, HTW, MTW, and LTW. Use applicable sections of NFGS-
15250 for other systems.
Insulation Thickness. Insulation thicknesses indicated in NFGS-
02696 and in NFGS-15250 are suitable for most geographic locations. However,
in locations where extreme annual temperatures occur, the project designer
should evaluate different thicknesses of insulation. Make final selection
based on an economic analysis in accordance with para. 2.3.5.
Jackets. Design insulation jackets in waterfront or other
locations subject to flooding to drain; they shall not be watertight.
requirements listed below.
Pitch. The surrounding terrain and piping application both affect
the pitch of piping as indicated below.
a) Horizontal Piping. Pitch horizontal steam piping down at a
minimum of 2-1/2 inches (64 mm) per 100 feet (30.5 m) of length in the
direction of steam flow.
b) Underground Piping. Pitch horizontal piping down towards drain
points (unless otherwise noted) a minimum of 2-1/2 inches (64 mm) in 100 feet
(30.5 m). Where the ground surface slopes in the opposite direction to steam
piping, step up underground piping in vertical risers at drip points in
manholes, and pitch them down to the next drip point. Use this method also
for all very long horizontal runs, above- or belowground, to keep piping
within a reasonable range of elevations with reference to the ground surface.
c) Counter-Flow Conditions. Where counter-flow of condensate
within the steam pipe may occur in a portion of a pipeline because the stepped
construction cannot be built, or because of steam flow reversal in a loop
system, pitch that portion up in the direction of steam flow a minimum of 6
inches (152 mm) per 100 feet (30.5 m) and increase pipe diameter by one
standard pipe size.
d) Compressed Air and Natural Gas Lines.
Pitch compressed air and
gas piping as for steam piping.