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During the loaded passage, the ballast tanks are normally empty, providing an opportunity to perform preventive and repair maintenance routines. Ballast system maintenance may include:
Repairs to ballast system valves and pumps in pumproom.
Hydrocarbon vapour testing of the ballast tank atmosphere at tank bottom (to detect any cargo tank bulkhead leaks).
Routine washing of ballast tank bottoms to remove/reduce sediment accumulation.
Entry and cleaning of ballast tanks to remove rust scale accumulation.
In-tank repairs of valves, actuators, or ballast level sensors
In-tank inspection of ship structure, coatings, or sacrificial anodes.

Any ballast tank entry for inspection, cleaning, or repair must be conducted in full compliance with owner's confined space entry procedures. Ballast tank entry must be treated just as cargo tank entry and all necessary confined space entry precautions observed. It takes only a small cargo leak to create a ballast tank atmosphere which is just as deadly as a poorly washed cargo tank. Ballast tanks must also be tested for oxygen before entry. Un-coated ballast tanks must always be considered to be oxygen deficient (due to corrosion), until thoroughly ventilated and tested at all levels. Coated ballast tanks should contain adequate oxygen immediately after they have been emptied, but should be ventilated and must be tested for oxygen before entry.
If cargo lines pass through the ballast tanks, the lines should be regularly placed under static pressure (by opening a valve to a full cargo tank) and the cargo pipelines inspected in the ballast tank(s) for any signs of leakage.
If sacrificial anodes are fitted in the tanks, they should be examined to see that they are being depleted as expected and to verify that their attachment is adequately secure.

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