Discharging Operations on Crude oil tankers

OIL TANKER OPERATIONS (Discharging)

Good planning is the hallmark of efficient tanker operations.

Prior arriving at the discharge port an exchange of information between the ship and the terminal will take place. Once the vessel is tied up at the terminal, a ship-shore checklist will have to be filled out. The general safety checks and precautions will be the same as given for the loadport. Since pumps will be running at the discharge port, special attention will have to be given to monitor the safe running of the pumps. Pumproom ventilation should be running throughout operations. Proper pumproom entry procedures should be followed. All crew should be aware of the fire and safety equipment available in the pumproom. Drips and leaks in the pumpFoom should be attended to immediately. Pumproom bilge soundings should be monitored regularly.

After completion of gauging/sampling and calculation the terminal will give indicate readiness for receiving the cargo. The chief officer will line up for discharge. Ideally cargo will be started by discharge from a single tank. In steam turbine cargo pumps it is important to warm up the pump gently. RPM of the pump will be slowly increased after all checks have been made. Inert gas will replace the volume of cargo discharged. The maximum oxygen content of the IG from the IG plant should be 5% and the tank should have a maximum of 8%. The IG pressure should be monitored very carefully to avoid over or under pressurizing of tanks.

When all checks have been completed, it will be safe to proceed to open up more tanks and start more pumps. Discharge pressure at the manifold to be monitored periodically.
The next important stage comes when a tank is nearing empty levels. When some oil is still left in the tank, the rpm of the pump should be reduced. Changeover procedure from one tank to another should be gradual. The valve of the tank nearing empty should be slowly throttled while the pump is fed by another tank which has a higher level of oil. Using the vac-strip pump or in its absence the stripping pump will be vital to avoid the pump misbehaving. In case a pump loses suction at any time, the rpm will increase dramatically. The pump should be stopped immediately in such a case or immediate measures should be taken to supply cargo oil to the suction side of the pump.

The use of a bar chart and thorough planning are the key points of an efficient discharge. Ballast should be taken into the ballast tanks as per the ballast plan worked out before arrival.

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