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Cargo tank rupture caused by increase of pressure - Emergency procedure for gas carriers

Cargo tank ruptures due to increased pressure are highly improbable with the existing tank protection systems. There are multiple devices/systems protecting the cargo tanks - it is almost impossible for all devices to fail at the same time. Additionally, cargo tanks may support much higher pressure than the actual settings of the relief valves. However in this scenario we have two different situations - whether the affected tank is loaded or empty: .

If the tank is empty the risk is less as no liquid cargo will be released. In that case, the hold space should be inerted at once.

If the tank contains cargo and it is liquid cargo that is released: A minor leak may be controlled by via the hold space ejector

LNG tanks internal barrier
LNG tanks internal barrier

A major leak may be impossible to control. In that case the two main options available are either abandonment or the jettisoning of the cargo

In either case the first indication will be by the one or more of the detection systems - the gas detector, level switch or temperature sensor.

Major Leak

If a major leak occurs and it can not be confined then jettisoning should be considered. Inerting of hold spaces shall be completed as described for a minor leak.

Sound general alarm

Stop cargo operation. Activate ESDS

Disconnect loading arms. Activate PERC

Leave jetty

As safety measure - Inert hold space where leakage (Cargo Tank rupture) has been detected until the O2% is reduced to 2%. Continue blowing inert gas to hold space in order to keep temperature as high as possible. Remember to open the hold space vent in order to avoid overpressure in the hold space

Transfer cargo to other tanks in order to empty the tank. Considering stability and stress factors

Consider - jettisoning. Remember two cargo pumps are required in order to have proper pressure

Consider - external assistance

Prepare fire-fighting equipment

Consider - abandonment. Prepare life-rafts, lifeboats

Minor Leak

If a small leak occurs the vessel will be able to handle the leak through the drip pan. The liquid will flow to the drip pan where liquid will be transferred by the eductor back to the tank. Driving liquid to the eductor is supplied by spray pump. (for Moss type LNG Carriers) Data to remember: The tank designer advises that if a cargo tank cracks an average of 8 liter/hour will be released. The Drip pan will be able to contain such kind of leakage for 15 days without transferring cargo to another cargo tank.

Release pressure in order to avoid further damages

Isolate the rest of the hold spaces

Transfer cargo to other tanks if possible, normally loaded passage all tanks full

The majority of liquefied gases are clean, non-polluting, products and create no danger to the marine environment. If however certain liquefied gases spill on to the sea you should be aware that they may:

The Data Sheets will give information on pollution, if any Pollution is most likely to occur during cargo or bunkering operations:
  • if the operation is not correctly monitored
  • if the cargo hose or loading arm connections are not properly made
  • when disconnecting cargo lines that have not been drained.
  • if moorings are not checked and excessive strain is placed on the cargo connections or the ship "breaks out" of the berth.
  • if cargo equipment is not properly maintained

  • Related Information:

    1. LNG tank leaks and immediate action by gas carriers

    2. Leaks from a Loading Arm due to Tidal or Current Effects

    3. Minor or major leaks from LNG tanks

    4. Risk of Overfilling of Cargo Tank during Loading

    LNG spill risk during marine transportation and hazards associated

    How to tackle fire on board LNG ship

    Fire fighting plan for LNG cargo

    Cargo conditioning, reliquefaction and boil-off control requirement for a liquefied gas carrier

    Cargo Containment Systems in Liquefied Gas Carriers

    cargo emergency shutdown requirement

    damage stability guideline for liquefied gas carriers

    Various Cargo handling equipments onboard

    Cargo hoses connection guideline

    Documents accompanying a liquid gas cargo

    How LNG transferred from shore to ships cargo tanks ?

    Cargo operation guideline onboard a liquefied gas carrier

    Cargo piping Systems in Liquefied Gas Carriers

    cargo planning requirement

    cargo and pumproom safety precautions

    cargo stripping guideline

    Emergency response for cargo system leaks

    Emergency response for cargo tank rupture

    Risk of overfilling of cargo tank during loading onboard a liquefied gas carrier

    Preparation for cargo transfer

    cargo transfer between vessels- safety guideline

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