Liquefied Gas Carrier

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Cargo system leaks - Emergency response for liquefied gas carriers

In the event of cargo system leaks & contact with LNG chilled to its temperatures of about –160 degree C will damage living tissue. Most metals lose their ductility at these temperatures; LNG may cause the brittle fracture of many materials. In case of LNG spillage on the ship’s deck, the high thermal stresses generated can result in the fracture of the steel.

Leaks on the Cargo System, Continuous Flow

This comprises all leaks that cannot be easily stopped by operational routines, rupture in a pipe.

i) Advise CCR (Terminal) / Bridge (Port/Sea) Location and dimension of the leak

ii) Activate ESDS or stop cargo operations

iii) Change course in order to get rid of vapour gas

iv) Advise terminal as to why ESDS has been activated

v) Try to stop the leak if that is possible (wrapping with wet rugs, tightening bolts)

vi) If leak cannot be stopped isolate leakage by means of closing valves

vii) Flush water in leak area

viii) Avoid any kind of external ignition source

ix) Make the dry powder system ready for possible outbreak of fire

x) Ensure that all doors, (hatches, etc.) opening to the upper deck from the accommodation area, (engine room etc..) are closed

xi) Stop ventilation fans if necessary. Put Air-conditioning in re-circulation mode if it is not already

xii) Activate water spray system if necessary

xiii) Consider - alternatives to continue loading/discharging operations

xiv) Consider - alternatives to continued spraying

xv) Consider - alternatives to continued cooling down of cargo lines, transferring cargo

xvi) Once situation has stabilised, consider - repairs (temporary or permanent)

xvii) Advise all parties involved Owners, Agent, Terminal, P&I if situation required

Collision - Involving uncontrollable escape of LNG cargo (MEMBRANE)

The event can only be described in a hypothetical context, as no such situation has actually occurred. The following is therefore based on theoretical studies and investigations.
  1. In the loaded condition with failure of the primary and secondary membranes, liquid cargo will pass through the primary, secondary barriers, inner hull and the ruptured ballast tank and out to the sea. As the membrane containment system is supported by the inner hull steel structure, failure of the inner hull due to the collision damage and embrittlement would lead to collapse of the membrane containment system in the damaged area. This would lead to a further major increase of the outflow of LNG.

  2. Ignition may not take place within the vessel due to the over-rich concentration of vapours. In such cases, the attempted separation of the vessel from a colliding vessel or other structure should not be attempted, if circumstances permit, in order to avoid the risk of creating an ignition source during separation. This despite the colliding vessel probably encountering hull structure failure from both the collision damage and the embrittlement from the outflow of LNG.

  3. The vaporisation of the spillage will initially form a heavy white vapour cloud and this is likely to quickly envelope the deck and accommodation areas. Hence it is essential that all potential sources of ignition are isolated and the decks cleared of all personnel.

  4. If separation has taken place from the colliding vessel or obstruction and there is no gas concentration in the propulsion machinery space, attempts should be made to manoeuvre in such a way as to place the vessel clear of the vapour cloud. This may involve steaming the vessel astern.

  5. As far as possible, the damaged tank and barriers should be isolated from other tanks and barriers. This will prevent both back flow of boil-off vapour from undamaged tanks to the ruptured tank and, at later stage, the possible admixture of air and cargo vapour in the whole cargo system.

  6. Flooding the ballast tanks adjacent to the damaged tank with sea water, where possible, will reduce the effect of embrittlement on the adjoining bulkheads and prevent gas vapour from entering undamaged tanks.

  7. The operation of water sprays and curtains will reduce the possibility of vapour cloud ignition on deck, assuming the deluge and fire main systems are still intact.

  8. If ignition does occur, the resulting fire may be such that the dry powder capacity onboard could be exhausted or, if the fire is extinguished, reserves have been run so low that any re-ignition could not be contained. Therefore, thought should be given to the desirability of allowing the fire to burn in a controlled manner.

  9. Before attempting to fight large fires, due consideration should be given to the possible options:
    i) Allowing a fire to continue to burn thus running the risk of the fire spreading and greater damage being caused.
    ii) Extinguishing the fire and running the risk of damage to life and property if unignited vapour is allowed to drift under light wind conditions to areas of high ignition risk.

  10. Where cargo is jettisoned, personnel should be aware of the Rapid Phase Transition (RPT) phenomenon. When LNG, particularly if the LNG is aged, is spilled on to water, a violent interaction can occur. This is the result of rapid vaporisation of the LNG, superheated by contact with water.

  11. A very careful check should be maintained on all intact cargo tanks, barriers and adjacent compartments.

  12. Once the situation has been stabilised and the stability of the vessel is secured, consideration can be given to the problem of what to do with the remaining cargo in the damaged tank.
    Factors will include:

    i) Damage to the vessel and quantity of remaining cargo.
    ii) The operational status of the propulsion machinery, cargo containment system and cargo transfer system.
    iii) The location of the vessel.
    iv) If the cargo containment system is intact, the possibility of ship to ship transfer may be considered.

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

  5. Connection and disconnection of cargo hoses and hard arms

Related Information:

  1. Procedure for Water washing after Ammonia Cargoes

  2. Procedure for Changing Liquefied Gas Cargoes

  3. Use of cargo as fuel -Cargo conditioning, reliquefaction and boil-off control for LNG carriers

  4. Displacing with Vapour of the Next Cargo (Purging)

  5. Dispersal of Vented Cargo Vapours

  6. Details of various cargo handling equipment onboard

More info pages

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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