The requirement of the cargo Emergency Shutdown (ESD) system are to stop cargo liquid and vapour flow in the event of an emergency and to bring the cargo handling system to a safe, static condition.
The earlier method of cargo shut down comprise of manual trip
points and automatic fire sensors that can initiate remote closure of emergency shutdown valves "for shutting down liquid
and vapour cargo transfer between ship and shore"
This emergency trip, when activated, must also stop
cargo pumps and compressors. However, these provisions do not necessarily provide adequate protection, particularly
against overflow, during other operations involving the transfer of liquid and vapour on board. It must be recognised
that operations such as reliquefaction or cargo tank spraying may be routine operations at sea. These deficiencies eliminated by intruducing cargo emergency shutdown (ESD).
The ESD system minimises potential risks during the transfer of liquefied gases between ship and shore loading and
unloading installations. It provides a quick and safe means of stopping the transfer of cargo and isolating ship and
shore cargo systems in a controlled manner, either manually or automatically, in the event of fault conditions that affect
the ability of the operator to control safely the transfer of cargo. Most export terminals, and an increasing number of
import terminals, now have a second level of protection providing for the rapid disconnection of the loading arms from
These two levels of cover are known as `ESD-1' and `ESD-2'.
The emergency shutdown (ESD) system is a requirement of the IMO code for the carriage of
liquefied gases in bulk and is a recommendation of SIGTTO. It is fitted to protect both the ship and
terminal in the event of power loss, cryogenic or fire risks, on either the ship or in the terminal.
The system will stop the flow of LNG liquid and vapour by shutting down the pumps and gas
compressors as well as manifold and shipside valves, by the activation of a single control. Shut
down of the cargo system can be initiated either manually or automatically if certain off-limit
The ship's ESD system is active at all times, whether at sea or in port. When at sea all manifold
and tank filling valves are held in the shut position and the cargo and spray pumps are held in the
off position. The cargo compressors may be operated as normal, but will stop if an ESD is initiated.
The shore ESD input is blocked in the At Sea DCS condition
Manual emergency shut down push buttons are situated strategically around the ship, at locations
that include the wheelhouse, cargo control room, fire control station, manifold platforms and tank
liquid domes. In addition, manual activation of the shore ESD system will, through the ship/ shore
link, set off the ship’s ESD.
Automatic shut down for fire is initiated by fusible plugs which are generally located at each tank
dome, manifold platform, and in the cargo compressor and electric motor rooms.
ESD1 may also be initiated automatically under conditions such as the following:
- Blackout of the ship.
- Vapour header pressure falls below pre-set limit.
- Individual tank pressure falls below pre-set limit.
- Extreme liquid level in any cargo tank.
- Low cargo valve hydraulic pressure.
ESD2 is normally initiated by the terminal and will result in all the actions as for ESD1, plus the
initiation of a dry break of the shore arm from the ship. ESD2 may be initiated manually, for
example, in the event of a terminal emergency, or automatically, for example, if the ship moves
outside the movement envelope of the chicksans.
The automatic disconnection of shore arms can be a violent and potentially dangerous operation
and it is important that personnel at the manifold are warned to leave the area before ESD2
Each ship must have procedures for testing the function of ESD systems which must be tested
prior to arrival in port and also immediately before commencing cargo operations.
Emergency shutdown (ESD) blocking and override
The ESD system will have a facility to activate a “block” or “override”. Under normal vessel
operating procedures the ESD system will be fully active, There may be occasions when it will be
necessary to inhibit part or all of the system.
The “At Sea” condition” will be selected prior to the shore connection being disconnected after the
cargo operations have been completed. The “At Sea” condition has the following effect:;
- Isolates the shore connection from the ESD logic
- Locks the cargo pumps in the OFF condition
- Positions the manifold valves in the CLOSED position
- Positions the cargo tank filling valves in the CLOSED position
- Allows the low duty compressors to run if the ESD or low duty system trips are not
- Allows the high duty compressors to run if the ESD or high duty system trips are not
Prior to any cargo operations in port, the “At Sea” condition must be switched to the “In Port”
position to allow the ESD system to be fully active.
After any emergency shutdown of the cargo system, it may be necessary to “Override” the system.
Before the system is switched to “Override” the cause of the shutdown must be determined. The
“override” facility should only be used when absolutely necessary to allow recovery from an emergency condition. As soon as the emergency condition is corrected, the ESD should be
returned to the normal condition and the “override” facility switched off.
Before the ESD is overridden, the Master must be fully appraised of the situation, and must give
his approval for the “Override” to be switched on.
It must be noted that on any occasion that the ESD is not in its normal operational condition, any
cargo related emergency situation on board the ship and or terminal, will not result in activation of
the ESD, and full shut down of the cargo system will not take place.
LNG vessels must always conduct pre-arrival ESD system tests 48 hours before arrival at any load
or discharge port. Additionally in the event of an extended voyage, the ESD system should again
be tested at intervals of not more than 30 days from the previous test.
These tests must include, but not be limited to:
- Cargo Emergency Shutdown system test, including all push buttons and trips (These may
be tested in rotation).
- All Cargo and Ballast valves operated.
- Manifold valve timings checked.
- Check the operating parameters of nitrogen generators and barrier space pressures (where
- Barrier space water detection (where applicable).
- Mast riser nitrogen snuffers.
- Ship-Shore interface connection operations.
Successful completion of these tests must be logged on form LNG02 and recorded in the deck log
Prior to loading / discharge operations in port, additional ESD testing in both the warm and cold
conditions will be carried out as part of the pre-transfer ship-shore checklist.
- Procedures for LNG cargo loading
- Manifold arrangements
- Procedures for LNG cargo discharging
- Boil-off & Vaporized Gas (BVG) Management System for LNG cargo
- Gas cargo containment systems - primary barrier (the cargo tank),secondary barrier, thermal insulation and more
- Details of various cargo handling equipment onboard
- Procedure for loading Liquefied Gas Cargoes
Procedure for Cargo Conditioning in Liquefied Gas Carriers
Cargo Transfer between Vessels (STS Operation)
Procedure for segregation of Liquefied Gas Cargoes
Procedure for Stripping Liquefied Gas Cargoes
Procedure for Changing Liquefied Gas Cargoes
Displacing Atmosphere with Inert Gas (Inerting)
Procedure for Water washing after Ammonia Cargoes
- Preparation for Cargo Transfer
Procedure for discussion prior cargo transfer
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