TM 5-848-1/AFM 88-12, Chap. 1
1. Scope
objectionable effects of dead ends can often be
relieved to some extent by looping such line
This manual contains instructions and engineering
around the area it serves and then back into itself.
information relating to gas distribution pipe sys-
At large stations it will usually be advantageous to
tems, including pressure regulators, valves, meters,
extend the high-pressure line to provide two or
and other necessary appurtenances, for the
more connections with the distributing lines for
distribution of fuel gas, natural and manufactured,
purposes of uniformity and assurance of adequate
from the point of delivery by the gas supplier 10 the
pressure.
points of connection with building piping. The
b. Line locations. Gas distribution system lines
appendix contains a list of references used in this
will never be installed under a building. They will
manual. A bibliography citing sources where addi-
not be laid in the same trench with other utilities to
tional information can be found is also attached to
preclude the possibility of leaking gas following
this manual.
along or collecting in other conduits and creating
2. Purpose.
an explosion hazard. For the same reason, gas lines
will be above other utilities whenever they cross, if
The purpose is to furnish a guide for designing new
practicable. Gas lines will not be laid under paved
gas distribution systems, for checking the adequacy
streets or in other locations subject to heavy traffic
of designs furnished by gas suppliers, and for
whenever practicably avoidable. Whenever it is
analyzing existing systems to determine their
necessary to locate gas lines in such locations, the
adequacy for supplying the demands of proposed
lines will be protected by suitable casing or by
additions.
burying to a depth to provide at least 2 feet of
3. Safety requirements.
cover over the top of the pipe. Sufficient clearance
must be maintained between plastic mains and
The design will include all safety requirements of
steam, hot water, power lines, and other sources of
ANSI B31.8 including guidance for abandoning gas
heat, to avoid temperatures in excess of 60 degrees
lines. The requirements of ANSI B31.8 are
C (140 degrees F) for thermoplastics or 66 degrees
adequate for safety under conditions normally
encountered in the gas industry. Requirements for
C (150 degrees F) for thermo-setting epoxy resin
all abnormal or unusual conditions cannot be
pipe.
specifically provided in this manual, nor are all
c. Drips. Drips will be installed at all low points
details of engineering prescribed.
in lines transmitting manufactured gas or a mixture
of natural and manufactured gas. In lines
4. Pressure classes of distribution sys-
transmitting natural gas, drips will be installed at
tems.
the low points immediately following reduction
a. Low-pressure system. In a low-pressure gas
from high pressure to low pressure and at occa-
distribution system, the gas pressure in the mains
sional low points throughout the system to provide
and service lines is substantially the same as that
for blowing out the lines.
delivered to the user's appliances. In such a system
d. Grading lines. Gas mains will be buried deep
a service regulator is not required on the individual
enough to provide at least 2 feet of cover over the
service lines.
top of the pipe. Where manufactured gas is used,
b. High-pressure systems. A high-pressure gas
the lines will be uniformly graded to drain the low
distribution piping system operates at a pressure
points to prevent the formation of pockets where
higher than the standard service pressure delivered
condensate could restrict the flow of gas. Lines
to the user. In such a system, a service regulator is
transmitting natural gas need not be graded but
required on each service line to control the
may follow the contour of the grounded surface.
pressure.
e. Value spacing in distribution systems.
Whether for operations or emergency uses, valves
5. System planning.
on distribution mains will be spaced as required in
a. Layout. Gas distribution systems will be
the following subparagraphs.
planned carefully with due consideration for econ-
(1) High-pressure systems. Valves will be in-
omy, safety, and uniformity of pressure. The lines
stalled in readily accessible locations to reduce the
will be well-looped within the main area and in all
time to shut down a section of a main in an
outlying areas whenever practicable and economi-
emergency. When determining the spacing of the
cally feasible to do so. It is not always practicable
valves, consideration should be given to the oper-
to loop a supply line to an outlying area and then
ating pressure and size of the mains and to local
back into the main system, but in such cases the
physical conditions as well as to the number and
Change 1
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