Regulation on Crude Oil Washing Requirements as per MARPOL

Crude Oil Washing (COW) Requirements:

• This regulation comes under MARPOL Annex I, Chapter 4 - Requirements for the Cargo Area of Oil Tankers, Part B - Equipment, Regulation 33.

• Every Crude Oil Tanker of 20,000 tonnes deadweight and above delivered after 1 June 1982, shall be fitted with a cargo tank cleaning system using crude oil washing.

• The Administration shall ensure that the system fully complies with the requirements of this regulation within one year after the tanker was first engaged in the trade of carrying crude oil or by the end of the third voyage carrying crude oil suitable for crude oil washing, which ever occurs latter.

• Crude oil washing installation and associated equipment and arrangements shall comply with the requirements established by the Administration.

• The requirements shall contain at least all the provisions of the specifications for the Design criteria, Operation requirements and Control & enforcement procedures for the Crude Oil Washing systems adopted by the Organization.

• A complete inspection of the crude oil washing equipment and arrangements shall be carried out, which includes an examination of the tanks after they have been crude oil washed to ensure that the washing efficiency is in accordance with the guidelines adopted by the Organization.

Specifications on Design of COW systems as per Resolution A.897(21)

Design Criteria:

Piping:

• The crude oil washing pipes and valves incorporated in the supply piping system shall be of steel or other equivalent material and shall be of adequate strength having regard to the pressure to which they may be subjected, and shall be properly jointed and supported.

• The COW system shall consist of permanent pipework and shall be independent of the fire mains and any other system other than for tank washing.

• The use of flexible hose pipe to connect the COW system to the tank washing machines if it is necessary to locate these machines in a cargo tank hatch cover.

• Such a flexible hose must be provided with the flange connexions and to be manufactured and tested in accordance with the standards acceptable to the Administration.

• Provision shall be provided to prevent the overpressure in the tank washing supply pipings.

• Any relief device fitted to prevent the overpressure shall discharge into the suction side of the supply pump. 

• Where hydrant valves are fitted for the water washing purpose on tank washing lines, all such valves shall be of adequate strength and a provision shall be made to blank the valve with blank flanges when the washing line is filled with crude oil.

• All connexions shall be provided with Pressure gauges with isolating valves adjacent to the lines unless the fitting is of the sealed type.

• No part of the crude oil washing system shall enter through the machinery space.  

• The piping system shall be tested to one and half time the working pressure after it has been installed on the ship.

• The pipelines shall be firmly attached to the ship's structure at appropriate location's and means shall be provided to permit free movement to accommodate thermal expansion, hydraulic shocks, and flexing of the ship.

Tank Washing Machines:

• The tank washing machine for COW shall be permanently mounted and shall be of a design acceptable to the Administration.

• Tank washing machines shall be fitted in such a way that, it shall have a characteristic such that the sections of the cargo tank covered by that machine will be effectively cleaned within the time specified in the Operation and Equipment Manual.

• Tank washing machine shall be mounted in each cargo tank and the method of support shall be to the satisfaction of the administration.

• Each machine shall be capable of being isolated by means of stop valves in the supply line.

• If the deck-mounted tank washing machine is removed for any reason, the provision shall be made to blank off the oil supply line to the machine for the period the machine is removed.

• A provision shall be made to close the tank opening with the plate or equivalent means.

• The number and location of tank washing machines shall be to the satisfaction of the Administration.

• The number and location of the machines in each cargo tank shall be such that all horizontal and vertical areas are washed by direct impingement or effectively by deflection or splashing of the impinging jet.

Pumps:

• The pumps supplying crude oil to the tank washing machine shall be either the cargo pumps or pumps specifically provided for the purpose.

• The capacity of the pumps shall be sufficient to provide the necessary throughput at the required pressure for the maximum number of tank washing machines required to be operated simultaneously as specified in the Operation and Equipment Manual.

• The pumping and piping arrangement shall be such that the crude oil washing system can be effectively operated with one pump out of use.

• The carriage of more than one grade of cargo shall not prevent crude oil washing of tanks

• The minimum supply pressure required for crude oil washing shall be specified in the Operation and Equipment Manual.

Stripping System:

• The design of the system for stripping crude oil from the bottom of every cargo tank shall be to the satisfaction of the administration.

• The design and capacity of the tank stripping system shall be such that the bottom of the tank being cleaned is kept free of accumulations of oil and sediments towards completion of the tank cleaning process.

• The stripping line shall be capable of removing oil at a rate of 1.25 times the total throughput of all tank cleaning machines to be operated simultaneously when washing the bottom of the cargo tanks as described in the Operations and Equipment Manual.

• Means shall be provided to drain all cargo pumps and cargo lines at the completion of cargo operation by connection to the stripping device.

• The means of stripping oil from the cargo tanks shall be by positive displacement pump, self-priming centrifugal pump or educator or other methods to the satisfaction of the Administration.

• Since the stripping lines are connected to a number of tanks, the means shall be provided for isolating each tank that is not being stripped at a particular time. 

• Equipment shall be provided for monitoring the efficiency of the stripping system, the monitoring system shall include, a flow indicator, or a stroke counter or a revolution counter and pressure gages at the suction and discharge connections of the pump.

Reference: 

IMO Publications & Documents - International Conventions - MARPOL - Annex I

IMO Publications and Documents - Specification and Manuals - Crude Oil Washing Systems - Resolution  A.897(21)