MIL-HDBK-1003/8A
3.3.5
Distribution Circuits. Select a circuit which is economical, easy
to operate, balance and control, and is suitable for a particular project
terrain. Note that types easiest to balance and control are those where
pressure and temperature differences are fairly constant between equipment
supply and return branches.
3.3.6
Route Types. Run distribution piping through buildings,
aboveground, or underground and below piers.
3.3.6.1
Through Buildings. Select the route considered technically and
economically best justified; make full use of building piers, underpiling
spaces, basements, crawl spaces, and attics, including connecting corridors
between buildings, existing tunnels and concrete trenches. However, high-
pressure fuel gas, steam, and HTW piping inside buildings should be routed to
comply with federal and local fire and life safety codes. Gas piping shall
comply with ANSI B31.8, Gas Transmission and Distribution Piping Systems, and
NFPA 54, National Fuel Gas Code. Steam, condensate and compressed air lines
shall comply with ANSI B31.1, Power Piping.
3.3.6.2
Exterior Steam Distribution. Use NFGS-02695 for all steam
distribution piping exposed to the weather, on building exteriors, aboveground
piping supports, piers (pedestals), poles, and for all steam piping on piers
and under piers, in tunnels and in manholes. Use NFGS-02693 for piping in
trenches. Use NFGS-02694 for buried steam piping .
3.3.6.3
Aboveground Overhead Piping. Locate piping as low as 1 foot
(305 mm) or as high as 22 feet (6.7 m) above the ground surface. A 16-foot
(4.9 m) clearance is required for automobile and truck traffic, and a 22-foot
(6.7 m) clearance for railroad cars.
3.3.6.4
Buried Piping. For buried piping routes, the following criteria
apply (refer to NFGS-02694):
a) Compressed Air and Gas Piping. Compressed air and gas piping
generally require no insulation, but they should be shop coated, wrapped,
tested, and handled in accordance with provisions of NFGS-02685, Exterior
Buried Natural Gas Distribution Systems, NFGS-02682, Exterior Fuel
Distribution System), and NFGS-09809, Protection of Buried Steel Piping and
Steel Bulkhead Tie Rods. Provide for testing of coverings by electrical flow
detectors (spark test).
b) Minimum Cover. Protect all buried piping and conduits by
laying them under a minimum cover of 24 inches (610 mm). However, protect
buried piping under railroads, roads, streets, or highways or due to changes
in ground contours against possible external damage due to the superimposed
car or truck traffic. Lay pipes below the frost line. Casings may be needed
where there is no frost.
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