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.
Preparation and approval by the Master of a Cargo plan including valve line up.
Calculation of Drafts, Stress and Stability for the vessel throughout the cargo operation and
the forthcoming voyage.
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.
Remote and if applicable local valve operation and remote indicators to be verified as in
synch with each other.
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.
Ballast water has been exchanged in line with international, Port State/Terminal and
company requirements.
Fire fighting equipment including hoses, dry powder units/guns and other appropriate
safety equipment in place and fully operational.
Fig:Liquid line cooling by LNG ship before discharging cargo
HD compressors ready for operation.
Sufficient Nitrogen is available for the cargo operation and forthcoming voyage. Nitrogen
equipment is operational and correctly lined up.
High High Alarms tested and verified as operational.
Overflow alarms and activation of the ESD system tested and recorded as operational.
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:
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