Only fixed tank washing machines may be used for crude oil washing.
The oxygen content of the tank must not exceed 8% by volume as described.
Before arriving in a port where it is intended to crude oil wash, the tank washing system should be pressure tested to normal working pressure and examined for leaks.
The system should be drained down after testing to avoid the risk of thermal expansion of the oil causing leaks.
Any leaks found should be made good, after which the system should be re-tested and proven leak-free.
During crude oil washing, the system must be kept under constant observation so that any leak can be detected immediately and action taken to deal with it.
When tanks for crude oil washing are being changed-over, the pressure in the COW line should be reduced to a minimum before any valves are opened or shut on the system, thereby minimizing the potential for damage due to surge pressure.
Mixtures of crude oil and water can produce an electrically charged mist during washing having potentials considerably in excess of that produced by ‘dry’ crude oil. The use of dry crude oil is therefore important. Before washing begins, any tank which is to be used as a source of crude oil for washing, should be partly discharged to remove any water which has settled out during the voyage. The discharge of a layer at least one metre in depth is necessary for this purpose.
For the same reason, if the slop tank is to be used as a source of oil for washing, it should first be completely discharged ashore and refilled with dry crude oil.
If the tank washing water heater is fitted outside the engine room, it must be blanked-off during crude oil washing to prevent oil from flowing through it.
Read More: OIL TANKERS & OPERATION