Liquefied Gas Carrier

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Preparation for discharging LNG cargo - gas carrier guide

Before arrival at a terminal prior discharging
: The following checks and procedures are to be regarded as the minimum before cargo operations can commence.
  1. Preparation and approval by the Master of a Cargo plan including valve line up.
  2. Calculation of Drafts, Stress and Stability for the vessel throughout the cargo operation and the forthcoming voyage.
  3. Cargo lines walked and checked, in correct status, particular attention to be paid to valves and blinds that are not frequently moved. After dry dock or maintenance particular attention is to be paid to blanks, flanges etc that may not have been tightened correctly.
  4. Remote and if applicable local valve operation and remote indicators to be verified as in synch with each other.

  5. Cargo pumps, spray/stripping pumps and where appropriate compressor motors to be megger tested and the results are logged. Operation of ballast valves and pumps to be verified.
  6. Ballast water has been exchanged in line with international, Port State/Terminal and company requirements.
  7. Fire fighting equipment including hoses, dry powder units/guns and other appropriate safety equipment in place and fully operational.

    Liquid line cooling by LNG ship before discharging cargo

    Fig:Liquid line cooling by LNG ship before discharging cargo

  8. HD compressors ready for operation.
  9. Sufficient Nitrogen is available for the cargo operation and forthcoming voyage. Nitrogen equipment is operational and correctly lined up.
  10. High High Alarms tested and verified as operational.
  11. Overflow alarms and activation of the ESD system tested and recorded as operational.
LNG carrier seaway

Preparation for LNG discharging

When terminal regulations allow, ship lines are to be cooled prior to arrival alongside. The operation is normally commenced 2 hours prior to arrival. LNG is normally supplied to the cargo liquid lines by one of the spray pumps. It is required that the pipelines be thoroughly circulated and cooled until final custody transfer measurement.

To avoid accident the best procedures is to circulate from the spray tank and back to the same spray tank. This avoids the risk of overflow. Once the vessel is berthed alongside the ships side water curtain should be started. The cargo arms can now be connected.

The manifold connection should be purged with N2 gas until the O2 contents is <1%. The manifold should be leak checked by N2 pressurization from shore and standard soapy water. Gas burning should be stopped prior to initial gauging.

After completion of CTM, manifold ESD valves should be opened and a warm ESD test carried out. Re-open ESD valves.

Confirm setting of all ship and shore valves are correct after notifying terminal start spray pump and slowly open the liquid manifold cool down valves.

If required, increase the flow from the spray pump by increasing the motor load, or increasing the spray line pressure. During this operation monitor the liquid header temperature to ensure it remains sufficiently cold. Shore will inform when they consider arm cool down as complete. Stop spray pump and carry out cold ESD.

Below is our additional guideline for handling LNG cargo:

Procedures for LNG cargo discharging

Precautions for LNG carrier during loaded passage

Preparation for loading LNG cargo

Drying of Cargo Tanks and preparation for loading LNG cargo

Inerting of Cargo Tanks prior loading LNG cargo

Gassing-up requirement for cargo tanks

Initial Cool Down of cargo tanks

LNG spill risk during marine transportation and hazards associated

Toxicity and associated health hazards in liquefied Gas Carrier

Safety check items prior loading LNG cargo

Related Information:

  1. Liquefied gas carrier safety training

  2. Increased Cargo Capacity for LNG ships & Advantages of the dual fuel diesel electric propulsion

Defining various gas carrier types

Fuel flexibility of LNG ships

LNG ship spillage risk

LNG shipment

Initial Cool Down of cargo tanks

Leaks on the Cargo System, Continuous Flow - how to prevent

LNG tank leaks and immediate action by gas carriers

Leaks from a Loading Arm due to Tidal or Current Effects

Minor or major leaks from LNG tanks

Procedures for LNG cargo discharging

External links :

  1. Cryogenic Fuels Inc. - Provides reliable, cost effective fully integrated LNG (liquefied natural gas) vehicular fuel systems

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