A special pipeline arrangement that sends the expelled gas vapors from a ship's cargo tank back to shore during loading.
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MAXIMUM ALLOWABLE WORKING PRESSURE
Maximum allowable working pressure is the maximum gauge pressure permissible in the top of a cargo tank for a designated temperature. This pressure is based on calculations for each element in a cargo tank using nominal thicknesses, exclusive of allowances for corrosion and thickness required for loadings other than pressure. It is the basis for the pressure setting of the pressure-relieving devices protecting the vessel which is known as the maximum allowable relief valve setting or MARVS. The design pressure may be used in place of the maximum allowable working pressure in cases where calculations are not made to determine the value of the latter.
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CASCADE RELIQUEFACTION CYCLE
A process in which vapour boil-off from cargo tanks is condensed in a cargo condenser in which the coolant is a refrigerant gas such as R22 or equivalent. The refrigerant gas is then compressed and passed through a conventional sea water-cooled condenser.
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GAS CONDENSATE
Reliquefied gases which collect in the condenser and which are then returned to the cargo tanks.
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DEEPWELL PUMP
A type of centrifugal cargo pump commonly found on gas carriers. The prime mover is usually an electric or hydraulic motor. The motor is usually mounted on top of the cargo tank and drives, via a long transmission shaft, through a double seal arrangement, the pump assembly located in the bottom of the tank. The cargo discharge pipeline surrounds the drive shaft and the shaft bearings are cooled and lubricated by the liquid being pumped.
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MARVS
This is the abbreviation for the Maximum Allowable Relief Valve Setting on a ship’s cargo tank — as stated on the ship’s Certificate of Fitness.
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HEEL
The amount of liquid cargo retained in a cargo tank at the end of discharge. It is used to maintain the cargo tanks cooled down during ballast voyages by re-circulating through the sprayers. On LPG ships such cooling down is carried out through the reliquefaction plant and on LNG ships by using the spray pumps.
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SUBMERGED PUMP
A type of centrifugal cargo pump commonly installed on gas carriers and in terminals in the bottom of a cargo tank. It comprises a drive motor, impeller and bearings totally submerged by the cargo when the tank contains bulk liquid.
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ELECTROSTATIC HAZARD
The hazards associated with the generation of electrostatic charges during the cargo tank washing should be carefully considered.
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EXPANSION TRUNK
A section of free space above the top of a oil cargo tank allowing for expansion of the oil with minimal free surface consequences.
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DRY CERTIFICATE
A document usually issued by the cargo surveyor noting that the cargo tank is empty, dry, and ready to receive cargo if loading, or that the tank is fully empty after discharging.
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