Section
2 Fuel gas supply
2.1 Supply requirements
2.1.1
General
- The requirements of Pt 11, Ch 16, 2 Fuel gas supply apply to fuel gas supply piping outside of the cargo
area. Fuel piping shall not pass through accommodation spaces, service
spaces, electrical equipment rooms or control stations. The routeing of the
pipeline shall take into account potential hazards due to mechanical damage,
such as stores or machinery handling areas. Provision shall be made for
inerting and gas-freeing that portion of the gas fuel piping systems located
in the machinery space.
2.1.2
Leak detection
- Continuous monitoring and alarms shall be provided to indicate
a leak in the piping system in enclosed spaces and shut down the relevant
gas fuel supply.
2.1.3
Routeing of fuel supply pipes
- Fuel piping may pass through or extend into enclosed spaces
other than those mentioned in Pt 11, Ch 16, 1.3 Arrangement of spaces containing gas consumers 1.3.1, provided it fulfils one of the following conditions:
- A double wall design with the space between the
concentric pipes pressurised with inert gas at a pressure greater
than the gas fuel pressure. The isolating valve, as required by
Pt 11, Ch 16, 2.1 Supply requirements 2.1.5, closes automatically upon loss of inert gas
pressure; or
- Installed in a pipe or duct equipped
with mechanical exhaust ventilation having a capacity of at least 30
air changes per hour, and shall be arranged to maintain a pressure
less than the atmospheric pressure. The mechanical ventilation shall
be in accordance with Pt 11, Ch 12 Artificial Ventilation in the Cargo Area as
applicable. The ventilation shall always be in operation when there
is fuel in the piping and the isolating valve, as required by Pt 11, Ch 16, 2.1 Supply requirements 2.1.5, shall close automatically if the required air
flow is not established and maintained by the exhaust ventilation
system. The inlet or the duct may be from a non-hazardous machinery
space, the ventilation outlet shall be in a safe location.
2.1.4
Requirements for fuel gas with pressure greater than 1 MPa
- Fuel delivery lines between the high pressure fuel
pumps/compressor and consumers shall be protected with a double walled
piping system capable of containing a high pressure line failure, taking
into account the effects of both pressure and low temperature. A single
walled pipe in the cargo area up to the isolating valve(s) required by Pt 11, Ch 16, 2.2 Spaces containing gas consumers 2.2.1 is acceptable.
- The arrangement in Pt 11, Ch 16, 2.1 Supply requirements 2.1.3.(a).(ii) may also be acceptable providing the pipe or trunk is
capable of containing a high pressure line failure, according to the
requirements of Pt 11, Ch 16, 2.2 Spaces containing gas consumers 2.2.3 and taking into account the effects of both pressure and
possible low temperature and providing both inlet and exhaust of the outer
pipe or trunk are in the cargo area.
2.1.5
Gas consumer isolation
- The supply piping of each fuel gas consumer unit shall be
provided with fuel gas isolation by automatic double block and bleed, vented
to a safe location, under both normal and emergency operation. The automatic
valves shall be arranged to fail to the closed position on loss of actuating
power. In a space containing multiple consumers, the shutdown of one shall
not affect the fuel gas supply to the others.
2.2 Spaces containing gas consumers
2.2.1
Piping aspects
- If the double barrier around the fuel gas supply system is not
continuous due to air inlets or other openings, or if there is any point
where single failure will cause leakage into the space, it shall be possible
to isolate the fuel gas supply to each individual space with an individual
master gas fuel valve, which shall be located within the cargo area. It
shall operate under the following circumstances:
- Automatically by
- Gas detection within the space;
- Leak detection in the annular space of a double
walled pipe;
- Leak detection in other compartments inside the
space, containing single walled gas piping;
- Loss of ventilation in the annular space of the
double walled pipe;
- Loss of ventilation in other compartments
inside the space, containing single walled gas piping;
- Manually from within the space, and at least one remote
location.
The isolation of fuel gas supply to a space, shall not
affect the fuel gas supply to other spaces containing gas consumers and
shall not cause loss of propulsion or electrical power.
- If the double barrier around the fuel gas supply system is
continuous, an individual master valve located in the cargo area may be
provided for each gas consumer inside the space. The individual master valve
shall operate under the following circumstances:
- Automatically by:
- Leak detection in the annular space of a double
walled pipe served by that individual master valve;
- Leak detection in other compartments containing
single-walled gas piping that is part of the supply system
served by that individual master valve;
- Loss of ventilation or loss of pressure in the
annular space of a double walled pipe;
- Manually from within the space, and at least one remote
location.
- It shall be possible to isolate the fuel gas supply to each
individual space containing a gas consumer(s) with an individual master gas
fuel valve, which is located within the cargo area. It shall operate under
the following circumstances:
- Automatically by:
- Gas detection within the space;
- Leak detection in the annular space of a double
walled space;
- Loss of ventilation in the annular space of the
double walled pipe;
- Manually from within the space, and at least one remote
location.
- The isolation of fuel gas supply to a space shall not affect
the gas supply to other spaces containing gas consumers.
2.2.2
Piping and ducting construction
- Fuel gas piping in machinery spaces shall comply with Pt 11, Ch 1 General to Pt 11, Ch 5, 4.2 Welding, post-weld heat treatment and non-destructive testing as applicable. The piping shall, as far as practicable,
have welded joints. Those parts of the fuel gas piping that are not enclosed
in a ventilated pipe or duct according to Pt 11, Ch 16, 2.1 Supply requirements 2.1.3, and are on the weather decks outside the cargo area,
shall have full penetration butt-welded joints and shall be fully
radiographed.
- The fuel gas piping in the machinery space is to be tested in
place by hydraulic pressure to 7 bar or twice the working pressure,
whichever is the greater. Subsequently, the lines are to be tested by air at
the working pressure using soapy water, or equivalent, to verify that all
joints are absolutely tight.
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