16.3.1 Gas fuel piping should
not pass through accommodation spaces, service spaces, or control
stations. Gas fuel piping may pass through or extend into other spaces
provided they fulfil one of the following:
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.1 the gas fuel piping should be a double wall piping
system with the gas fuel contained in the inner pipe. The space between the
concentric pipes should be pressurized with inert gas at a pressure greater than
the gas fuel pressure. Suitable alarms should be provided to indicate a loss of
inert gas pressure between the pipes; or
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.2 the gas fuel piping should be installed within a
ventilated pipe or duct. The air space between the gas fuel piping and inner wall
of this pipe or duct should be equipped with mechanical exhaust ventilation having
a capacity of at least 30 air changes per hour. The ventilation system should be
arranged to maintain a pressure less than the atmospheric pressure. The fan motors
should be placed outside the ventilated pipe or duct. The ventilation outlet
should be placed in a position where no flammable gas-air mixture may be ignited.
The ventilation should always be in operation when there is gas fuel in the
piping. Continuous gas detection should be provided to indicate leaks and to shut
down the gas fuel supply to the machinery space in accordance with 16.3.10. The master gas fuel valve required by 16.3.7 should close automatically, if the required air flow
is not established and maintained by the exhaust ventilation system.
16.3.2 If a gas leak occurs,
the gas fuel supply should not be restored until the leak has been
found and repaired. Instructions to this effect should be placed in
a prominent position in the machinery spaces.
16.3.3 The double wall piping
system or the ventilated pipe or duct provided for the gas fuel piping
should terminate at the ventilation hood or casing required by 16.3.4.
16.3.4 A ventilation hood or casing should be provided for
the areas occupied by flanges, valves, etc., and for the gas fuel piping, at the gas
fuel utilization units, such as boilers, diesel engines or gas turbines. If this
ventilation hood or casing is not served by the exhaust ventilation fan serving the
ventilated pipe or duct as specified in 16.3.1.2, then it should be equipped with an exhaust ventilation
system and continuous gas detection should be provided to indicate leaks and to shut
down the gas fuel supply to the machinery space in accordance with 16.3.10. The master gas fuel valve required by 16.3.7 should close automatically if the required air flow is not
established and maintained by the exhaust ventilation system. The ventilation hood or
casing should be installed or mounted to permit the ventilating air to sweep across the
gas utilization unit and be exhausted at the top of the ventilation hood or casing.
16.3.5 The ventilation inlet
and discharge for the required ventilation systems should be respectively
from and to a safe location.
16.3.6 Each gas utilization
unit should be provided with a set of three automatic valves. Two
of these valves should be in series in the gas fuel pipe to the consuming
equipment. The third valve should be in a pipe that vents, to a safe
location in the open air, that portion of the gas fuel piping that
is between the two valves in series. These valves should be arranged
so that failure of the necessary forced draught, loss of flame on
boiler burners, abnormal pressure in the gas fuel supply line, or
failure of the valve control actuating medium will cause the two gas
fuel valves which are in series to close automatically and the vent
valve to open automatically. Alternatively, the function of one of
the valves in series and the vent valve can be incorporated into one
valve body so arranged that, when one of the above conditions occurs,
flow to the gas utilization unit will be blocked and the vent opened.
The three shut-off valves should be arranged for manual reset.
16.3.7 A master gas fuel
valve that can be closed from within the machinery space should be
provided within the cargo area. The valve should be arranged so as
to close automatically if leakage of gas is detected, or loss of ventilation
for the duct or casing or loss of pressurization of the double wall
gas fuel piping occurs.
16.3.8 Gas fuel piping in
machinery spaces should comply with sections 5.2, 5.3, 5.4 and 5.5 as far as found applicable. The piping
should, as far as practicable, have welded joints. Those parts of
the gas fuel piping, which are not enclosed in a ventilated pipe or
duct according to 16.3.1 and are
on the open deck outside the cargo area should have full penetration
butt welded joints and should be fully radiographed.
16.3.9 Provision should be
made for inerting and gas-freeing that portion of the gas fuel piping
system located in the machinery space.
16.3.10 Gas detection systems
provided in accordance with the requirements of 16.3.1 and 16.3.4 should comply with 13.6.2 and 13.6.4, 13.6.5, 13.6.6, 13.6.7 and 13.6.8 as applicable; they should activate
the alarm at 30% of the lower flammable limit and shut down the master
gas fuel valve referred to in 16.3.7 before
the gas concentration reaches 60% of the lower flammable limit.