MIL-HDBK-1022
a) For steel piping systems, use weld neck forged or
rolled steel flanges with raised faces having a modified
spiral serrated gasket surface finish.
b) Do not use cast iron flanges.
c) Do not use grooved pipe type couplings or similar
fittings in permanent fixed piping systems.
d) Do not direct bury flanges, valves, mechanical
couplings, threaded fittings, or any mechanical equipment. If
they must be used in an underground system, enclose them in an
accessible pit.
e) Use welded connections for joining steel pipe.
Use flange connections for joining pipe to equipment. Use
threaded connections only where unavoidable such as on
differential pressure gages, pressure snubbers, and fuel
sample points.
f) In steel piping systems, use socket weld joints
on 2-inch (50 mm) diameter nominal size and smaller pipe.
g) Make branch connections with butt welded tees
except where the branch is at least two pipe sizes smaller
than the run, in which case the branch connection can be made
with a forged or seamless branch outlet fitting, which is
designed in such a way that the connection can be
radiographed.
h) Do not use wrinkle bends or mitered bends for
changes in direction.
i) Do not use threaded joints in aluminum piping
systems.
j) Except for unions and control tubing couplings,
do not use threaded joints in stainless steel systems.
Socket-weld stainless steel drain, vent, and pressure relief
valve lines 2-inch (50 mm) in diameter or less. If
aboveground, flanges may be used.
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