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Routine and required tank washing equipment maintenance should be carried out during the loaded passage. This will include maintenance to the water washing equipment and any crude oil washing (COW), equipment required by company procedures or, at a minimum, by IMO guidelines.

4.12.1 COW equipment maintenance
Before arriving at a discharge port where COW operation will be conducted, a COW system pressure test should be conducted. The test pressure used should be normal working pressure. The lines tested must be completely filled with cargo and the working pressure held constant while all sections of the lines are examined for leaks. The working pressure is that pressure at which the relief valves are set, or if no relief valve is fitted, the highest pressure which the supply pump can achieve.
If leaks are found, they must be repaired before COW operations are conducted and the repairs pressure tested before COWing begins. Thrust stoppers in way of expansion joints and dresser couplings should receive particular attention.
All COW machines should be operated for a short period to test for leaks beyond their shut off valves.
At least 24 hours before arrival at the offloading terminal, the following preparations must be completed:
Notify the terminal that the ship intends to COW while discharging.
Complete and transmit the standard terminal radio checklist (if applicable).
Complete and post a combined discharge and COW plan.
Verify that the ship's organization, duties and responsibilities plan has been drawn up.
Verify proper function and calibration of the portable and fixed oxygen analyser equipment.
Isolate the tank washing system from all engine room and water heater connections by means of blinds or blanks.
Verify that all COW line hydrant connections are blanked off.
Verify that all valves to fixed tank washing machines are closed.
Fit portable COW drive units (if applicable).
Verify correct function and calibration of the pressure gauges on the discharge line, the manifold and the tank cleaning main line.
Verify correct function and calibration of all stripping system monitoring equipment and instruments.
Verify correct operation of the communications system.

4.12.2 Water tank washing equipment
The water washing equipment should be gone through with particular attention to the safety aspects of the gear.
Tank washing machine safety ropes should be carefully examined and replaced if they show signs of wear. Only manila or sisal lines should be used, never synthetic lines. The line should be properly spliced into the lifting eye provided on the machine, or else provided with a suitable eye splice for looping snugly about the machine's top end.
Tank washing machines should be examined for damage and freedom of movement. Sufficient spare machines or parts should be carried to provide for replacement of damaged units. The machines should be flushed with fresh water after use. In some types a few drops of oil should be applied to the impeller shaft bearing and the impeller rotated two or three times with a screwdriver after each use. Then stow the machine in a dry place. Inspect the water passages at the inlet and nozzles for foreign material. Unscrew the nozzle tips to do this. If the impeller shaft, nozzles, or the body will not rotate freely the machine needs service or replacement.
The tank washing hoses should be examined for damage to the rubber carcass and end fittings. The threads on the end fitting should be cleaned with a wire brush, along with the threads on the washing main hydrants. On every voyage the electrical continuity of the tank washing hoses should be checked. This must be done in a well ventilate place, clear of any hydrocarbon vapours. The two ends of the hose should be brought together, but not touching, placed on a board or rubber sheet to prevent electrical contact with the deck. Using the resistance scale on a multi-meter check the resistance of the hose from coupling to coupling. On new 15 meter hoses, the resistance should be 11 to 12 ohms. The resistance of 15 meter hoses should never be more than 40 ohms. Hoses with broken bonding wires customarily show readings of 1000 ohms or more.
Hoses which show high resistance should be removed from service by cutting off one end, or (if under warranty or lease), placed in a secure area, clearly marked 'CONDEMNED - DO NOT USE' and returned ashore at the next port.

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