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Filling Limits for Cargo Tanks on Liquefied Gas Tankers

This article talks about Cargo Tank Filling Limits (higher filling limitFL, and maximum loading limitLL) on different types of gas carriers.

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General

No cargo tanks shall have a higher tank filling limit (FL) than 98 % at the reference temperature, except as permitted beyond.

The maximum loading limit (LL) to which a cargo tank may be loaded shall be determined by the following formula:

LL=FLρRρL,

  • LL – loading limit expressed in percent which means the maximum allowable liquid volume relative to the tank volume to which the tank may be loaded;
  • FL – filling limit as specified above;
  • ρR – relative density of cargo at the reference temperature;
  • ρL – relative density of cargo at the loading temperature and pressure.
LNG Cargo tank
Inside in the tank on LNG tanker

The society may allow a greater filling limit (FL) than 98 % in beginning of this article at the reference temperature, taking into account the shape of the tank, arrangements of pressure relief valves, accuracy of level and temperature gauging and the difference between the loading temperature and the temperature corresponding to the vapour pressure of the cargo at the set pressure of the pressure relief valves, provided the conditions of “Cargo Temperature Control and Cargo Vent Systems”Cargo Vent Systems are maintained.

For the purpose of this article only, “reference temperature” means:

  1. The temperature corresponding to the vapour pressure of the cargo at the set pressure relief valves when no cargo vapour pressure/temperature control as referred to in “Cargo Temperature Control and Cargo Vent Systems”Cargo temperature control and Vent system is provided.
  2. The temperature of the cargo upon termination of loading, during transport, or at unloading, whichever is the greater, when a cargo vapour pressure/temperature control as referred to in “Cargo Temperature Control and Cargo Vent Systems”Cargo temperature control and Vent system is provided. If this reference temperature would result in the cargo tank becoming liquid full before the cargo reaches a temperature corresponding to the vapour pressure of the cargo at the set pressure of the relief valves required in “Cargo Temperature Control and Cargo Vent Systems”Pressure and Temperature Control, an additional pressure relieving system complying with “Cargo Temperature Control and Cargo Vent Systems”Additional pressure relieving system for liquid level contro is to be fitted.

The Society may allow type C tanks to be loaded according to the following formula provided that the tank vent system has been approved in accordance with “Cargo Temperature Control and Cargo Vent Systems”Cargo Vent Systems:

LL=FLρRρL,

  • LL – loading limit expressed in percent which means the maximum allowable liquid volume relative to the tank volume to which the tank may be loaded;
  • FL – filling limit as specified above;
  • ρR – relative density of cargo at the highest temperature which the cargo may reach upon termination of loading, during transport, or at unloading, under the ambient design temperature conditions described in “Cargo Temperature Control and Cargo Vent Systems”Cargo temperature control and Vent system;
  • ρL – relative density of cargo at the loading temperature and pressure.

This paragraph does not apply to products requiring a type 1G ship.

Information to be provided to the master

The maximum allowable loading limits for each cargo tank shall be indicated for each product which may be carried, for each loading temperature which may be applied and for the applicable maximum reference temperature, on a list to be approved by the Society. Pressures at which the pressure relief valves, including those valves required by “Cargo Temperature Control and Cargo Vent Systems”Additional pressure relieving system for liquid level contro, have been set shall be stated on the list. A copy of the list shall be permanently kept on board by the Master.

This article applies to all ships regardless of the date of construction.

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