Appendix LR 6 - Use of Liquefied Petroleum Gas (LPG) Cargo as Fuel

1 General

1.1 Use of liquefied petroleum gas (LPG) as fuel is subject to agreement by the Administration, as required by 16.9.1.

1.2 The requirements given in Sections 16.1 to LR 16.10 are to be applied to ships which use LPG cargo as fuel in machinery spaces of Category A, as applicable and as amended by the requirements of this appendix.

1.3 The requirements in this appendix apply to LPG which is composed of propane or butane or mixtures of both unless specifically identified otherwise.

1.4 References to ‘gas’ in the requirements in Chapter 16 are to be taken as referring to LPG.

1.5 A risk-based study as described in LR 16.9-01 and LR 16.9-02 is to be carried out. The following are also to be considered:

• LPG fuel system leakages and spills and their consequences, particularly the accumulation of LPG vapours at low points and their spreading over the ship's spaces through openings.
• Risks associated with any LPG fuel storage tanks locations such as the open deck.
• The location for leak detection in LPG fuel system is to be assessed by means of a gas dispersion analysis where gas shall be present outside the cargo area.
• Vent arrangements, including the possibility of two-phase release from any pressure relief system and the requirement for a blowdown vessel.
• Instrumentation and control system failure conditions, considering criticality and safety requirements.
• Failsafe positions of all remotely operated valves in the LPG fuel system.

1.6 In addition to the information and plans required in Section 16.1, the following are to be submitted for consideration:

• Risk-based study report as defined in Section 16.9.
• Details and schematic of vent mast (if separate from the cargo venting arrangements).
• Details and schematic of ventilation systems in spaces containing LPG piping and LPG consumers.
• Purging calculations and procedure for gas freeing the LPG piping after shutdown of the gas consumers. This is to include minimum nitrogen capacity requirements for shutdown operations (normal and emergency shutdown).
• Details and schematic of LPG detection system, see 13.6.17.
• Details and schematic of engine crankcase ventilation system.
• Plans and capacity calculation of safety relief valves fitted within the LPG fuel system.
• Calculations of the thermal impact are to be provided in accordance with 4.4 in this appendix.
• Emergency shutdown system including detailed ‘cause and effect’ matrix.

2 Use of LPG cargo vapour/liquid as fuel

2.1 The set point value of the Exhaust Gas High Temperature alarm required by Pt 5, Table 2.7.1 Engines for propulsion purposes: Alarms and slow-downs of the Rules and Regulations for the Classification of Ships, July 2018 shall be calculated to ensure that the uptake exhaust temperature at the funnel outlet is at least 10 per cent below the fuel gas auto-ignition temperature.

3 Arrangement of spaces containing LPG consumers

3.1 Gas detectors are to be fitted as defined in 16.3.2, and consideration shall be given to the locations, such as the bottom of spaces where LPG is likely to be present, and in the ventilation outlets.

3.2 Depressurisation lines containing liquid fuel shall be led to either cargo tanks, dedicated LPG fuel tanks, blowdown vessels or knockout drums. Blowdown vessels or knockout drums connected to the vent mast are to be provided with a means to detect and dispose of any liquid fuel.

4 LPG fuel supply

4.1 For LPG fuel pipes installed in pipes or ducts, in addition to 16.4.3.2, the ventilation shall be arranged to ensure efficient air flow at the lowest point of the annular space. Both the inlet to and outlet from the ventilated pipe or duct are to be located in a safe location in the cargo area.

4.2 Gas consumer isolation by automatic double block and bleed valve, given in 16.4.5, is to be arranged in a way that the LPG fuel system is safely depressurised and LPG fuel is vented to a safe location in the cargo area in accordance with 8.2.12.

4.3 Non-continuous double barriers as described in 16.4.6.2 are not permitted on ships using LPG as fuel.

4.4 Thermal stresses in pipework resulting from leakage and rapid expansion of LPG are to be evaluated.

4.6 For double wall fuel piping systems containing high pressure liquid fuel in the inner pipe, the design pressure of the outer pipe or duct shall not be less than the maximum working pressure of the inner pipe unless the design pressure of the outer pipe or duct has been based on calculations demonstrating the duct or pipe integrity to safely contain a failure of the inner pipe or, alternatively, the strength has been verified by representative testing.