MIL-HDBK-1022
relief pressure created by the additive effect of these delta
pressure-type valves does not exceed the maximum pressure
rating of the system component with the lowest pressure
rating. See Facility Plate Nos. 026 through 029. If the
additive effects of cascading pressure relief valves produce
excessive pressure, consider using a series of ball check
valves around each shutoff valve to relieve thermal expansion
back to storage. For any isolated pipe segment on which the
relief valve discharge cannot be connected as described above,
provide a vented aboveground or below ground sump tank of
suitable capacity which is equipped to be emptied by means of
a portable pump. Equip the sump tank with self-checking high
level alarms and containment. Provide valves used for relief
of thermal expansion of not less than 3/4-inch (20 mm) nominal
pipe size. Require valves to be set to open at a pressure
approximately 10 percent above the operating pressure of the
line. Use a ball valve with handle removed on both inlet and
outlet sides. Provide visual sight glass downstream of all
pressure relief valve piping discharging to a recovery tank or
a return line. Locate relief valves and sight glass between
ball valves with removable handles.
9.3
UNDERGROUND PIPING. Provide underground piping
which passes under public roadways or railroad tracks in
accordance with Department of Transportation regulations
49 CFR 195 and API RP 1102. Refer to Section 2 of this
handbook for corrosion protection and for environmental
protection. Before installing underground pipelines, review
all local, state, and federal regulations for double wall
pipe, leak detection, and corrosion protection requirements.
9.3.1
Depth of Cover. Use the following criteria for
depth of cover over buried fuel pipelines:
a) Locate top of lines below design frostline and at
a minimum of 3 feet (0.9 m), except that less cover is
permissible for occasional stretches where overriding
conditions exist, such as the need to pass over a large
culvert or beneath drainage ditches. At such locations, build
sufficient slack into the line to allow for vertical and
lateral movement due to frost heave. Refer to Corps TM 5-852
series for additional guidance. Protective measures, such as
the installation of reinforced concrete slabs above the pipe,
may also be required where depth is less than required under
Paragraph (b) below.
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