MIL-HDBK-1005/7A
7.2.5
Pipe Installation . Except in special cases, all pipes
should be buried with a minimum cover of 2.5 ft. Where frost
penetration exceeds 2.5 ft, as indicated on National Weather
Service charts, the depth of cover should be increased to 6 in.
below the maximum recorded depth of frost penetration based on
local records in the area of installation. See Figure 1 for
generalized frost information.
7.2.5.1
Exposed Pipe . Exposed pipe may be placed on bridges
or piers for crossing streams or ravines. Exposed nonmetallic
pipe may be used only in climates not subject to freezing.
Exposed cast iron or steel pipe subjected to freezing should be
insulated or protected.
7.2.5.2
Inspection. All large conduits should be accessible
for internal inspection.
a)
Joints.
Refer to par. 7.1 for recommended
joints.
b)
Trenches, Backfill, Anchors, and Supports. Refer
to par. 7.1 for criteria related to trenches, backfill, anchors,
and supports.
c)
Railroad Crossings.
Refer to par. 7.1 for
criteria for railroad crossings.
d)
River C rossings.
Refer to par. 7.1 for criteria
for river crossings.
e)
Valves. Refer to par. 7.4 for detailed
information on valve types, applications and characteristics.
The following paragraphs pertain to transmission line valves.
(1) Provide air release valves as required based
on an analysis of the system. For flexible pipe which might
collapse under a vacuum, place vacuum valves as necessary, based
on an analysis of the system; also adjacent to each shutoff
valve on the downstream side. An active building service
connection at a summit may serve as an air release valve.
(2) Provide a blowoff at each depression for
draining the pipe. The minimum size of blowoff valves should be
2 in. for every foot of diameter of the pipeline.
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