MIL-HDBK-1022
b) Most systems designed in accordance with this
manual will have ANSI Class 150 flanges and a maximum
allowable working pressure of 285 psig (2000 kPa) at 100
degrees F (38 degrees C) for carbon steel and 275 psig (1900
kPa) at 100 degrees F (38 degrees C) for stainless steel
systems. This means that the total pressure including surge,
pump shutoff pressure, and static pressure in any part of the
system should never exceed those maximum allowable working
pressures. Other equipment items such as tank trucks,
aircraft fuel tanks, or shipboard fuel tanks which may be
damaged by shock pressures may require lower maximum surge
pressure. Assume a near instantaneous shut-off by the
aircraft in the design of aircraft hydrant systems.
c) Do not use manual calculations instead of
computer modeling when system surge pressures are crucial and
the piping system is complex. However, for simple piping
systems that operate under 80 psi (550 kPa), use the following
calculations to ascertain if surge is a problem:
(1) Determine the critical time of the system.
This is defined as the time it takes for the first increment
of the pressure wave to travel upstream, reflect, and return
to the valve. Use the following equation:
EQUATION: Tc = 2L/a
(1)
where:
Tc =
critical closure time of system(s)
L=
length of pipe (ft or m)
a=
surge pressure wave velocity (fps or m/s)
Values for "a" for liquid petroleum in schedule 40
steel pipe are as follows. These values are based on
hydrocarbons with a specific gravity of 0.8 at a temperature
of 68 degrees F (20 degrees C):
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