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:
1. 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
2. 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, 2.1 Supply requirements 2.2.1 is acceptable.
The arrangement in Pt 11, Ch 16, 2.1 Supply requirements 2.1.3 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, 2.1 Supply requirements 2.2.2 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:
1. Automatically by
  1. Gas detection within the space;
  2. Leak detection in the annular space of a double walled pipe;
  3. Leak detection in other compartments inside the space, containing single walled gas piping;
  4. Loss of ventilation in the annular space of the double walled pipe;
  5. Loss of ventilation in other compartments inside the space, containing single walled gas piping;
2. 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:
1. Automatically by:
  1. Leak detection in the annular space of a double walled pipe served by that individual master valve;
  2. Leak detection in other compartments containing single-walled gas piping that is part of the supply system served by that individual master valve;
  3. Loss of ventilation or loss of pressure in the annular space of a double walled pipe;
2. 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:
1. Automatically by:
  1. Gas detection within the space;
  2. Leak detection in the annular space of a double walled space;
  3. Loss of ventilation in the annular space of the double walled pipe;
2. 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 5, 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.

2.2.3 Gas detection

Gas detection systems provided in accordance with the requirements of this chapter shall activate the alarm at a relatively low per cent LFL (typically 20 per cent of the LFL in air) and shut down the master fuel gas valve required by Pt 11, Ch 16, 2.1 Supply requirements 2.2.1. at not more than 60 per cent LFL. See also Pt 11, Ch 13, 1.6 Gas detection 1.6.17.