TM 5-848-1/AFM 88-12, Chap. 1
(f) A series regulator as described in (1)(e)
standards on plastics. In addition, the latest infor-
above.
mation issued by manufacturers of plastic pipe, or
(3) Design requirements for pressure relief and
piping components will present in detail the special
pressure limiting devices. Such devices will:
or specific properties and recommendations related
(a) Be constructed of materials normally
to their products.
resistant to atmospheric corrosion externally and
(2) Plastic piping materials are significantly
gas corrosion internally.
more resistant to corrosion than metallic piping
(b) Have valves and seats designed so they
materials being used for the distribution of natural
will not stick in positions which prevent the devices
and other fuel gases. Galvanic corrosion of plastics
from operating properly.
does not occur since all plastics are nonconductors
(c) Be designed and installed for easy main-
and are not subject to electrochemical reactions as
tenance operation to check for leakage, pressure
are metals.
rate actuation, and free valve movement.
(3) All plastic pipes are significantly lighter than
(4) Telemetering or recording gauges.
the same size metal pipes. Compared to steel pipe,
(a) Each distribution system supplied by more
weight advantage varies from approximately 8 to 1
than one district pressure regulating station must be
for polyethylene pipe to about 4 to 1 for
equipped with telemetering or recording pressure
fiberglass pipe; thus it is easier for the construction
gauges to indicate the gas pressure in the district
crews to handle the plastic pipe.
line.
7. Miscellaneous.
(b) On distribution systems supplied by a
single district pressure regulating station, the
a. Odorization. A suitable malodorous agent
designer will determine the necessity of installing
will be injected into any gas which does not possess
telemetering or recording gauges in the supply line,
a natural distinctive odor for the purpose of detect-
taking into consideration the number of buildings
ing leaks. Unless the gas in the supply lines has
supplied, the operating pressures, the capacity of
already been odorized by the gas supplier, it will be
installation, and other operating conditions.
necessary to provide facilities for injecting a
malodorant. A storage tank and controlled device
6. Materials and equipment.
for injecting the odorizing agent at a rate that is
a. General requirements. Materials and equip-
proportional to the rate of gas flow, as determined
ment which will become permanent components of
by pressure drop across an orifice, will be required.
a gas distribution system will be suitable and safe
The point of injection will be on the downstream
for the conditions in the locality in which they are
side of the central regulating and metering station.
to be installed. As a minimum, components will
Recommendations can usually be obtained from gas
meet the safety requirements of Title 49, Code of
suppliers for type and quantity of malodorant to
Federal Regulations, Part 192. To the extent prac-
use and for suitable injecting equipment.
b. Liquefied petroleum gas (LPG) systems.
ticable, all materials will meet the requirements of
ANSI B31.8 and the approval of the gas supplier.
(1) Liquefied petroleum gases usually include
Plastic or steel pipe is preferred for distribution
butane and propane or mixtures of them which can
systems. Cathodic protection is mandatory for un-
be stored as liquids under moderate pressures of
derground ferrous gas distribution lines. Design of
80-250 psig at ambient temperature.
cathodic protection will be in accordance with TM
(2) LPG gas distribution systems will be de-
5-811-7. Stations will be provided for testing the
signed to comply with the requirements of NFPA
cathodic protection system.
58 instead of ANSI B31.8. Polyethylene and fiber-
b. Equipment specifications. The designer must
glass pipe will not be used in LPG systems.
specify equipment compatible with the system's
8. Plans and engineering data.
materials and operating requirements. In every
case, the safety requirements for equipment in a gas
a. Plans. The plans will include a layout drawing
piping system will be comparable with those of the
showing the entire distribution system and detail
piping components.
drawings clearly showing pipe sizes, the location of
c. Plastic pipe.
gas mains, service connections, details for
(1) In view of the rapid progress of technology
abandoning gas piping, valves, and regulators.
in the field of plastic pipe materials, engineers
ANSI B31.8 requires that abandoned gas lines be
should consult the latest issues of the AGA Plastic
physically disconnected from gas sources. Shutoff
Pipe Manual for Gas Service; Title 49, Code of
valves are not an acceptable means of disconnect.
Federal Regulations, Part 192; and the ASTM
Change 1
5
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