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maritime DC & PPE Information Center
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Types of Tanks

The interior of a ship is divided into compartments by transverse and longitudinal bulkheads and deck, which are an integral part of the structure. Compartments next to the shell at the ends, sides and bottom of the ship are normally used as tanks. Tanks are designated according to the material that they contain or the function they perform. A term, such as “fuel oil” and “potable water,” before a tank’s name is such a designation. The fluid contained in the tank establishes the corrosive environment of the substrate to be protected and the coating system installed. Other factors may increase or decrease corrosiveness of the environment. These factors include:

  • Temperature of the stored material.

  • Presence of dissolved oxygen.

  • Presence of chemicals and contaminants in the fluid medium (e.g., Chlorides, pH, Waste).

  • Presence of biological organisms and byproducts.

Tanks normally have sounding tubes to check the level of liquid in the tank. Tanks normally have air vents (escapes) to allow air to fill the tank when it is being pumped out or to allow air to escape when the tank is being filled. Tank accesses are limited and bolted. Tanks are considered as confined spaces because of their location in the ship, limited access and lack of air transfer. Further, corrosion in a tank can readily deplete the oxygen content of the air in the tank. For most tanks and voids on Naval vessels, premature failure of the coating system in such areas cannot be detected by routine observation without laying up of the ship’s tanks. Tank cleaning and inspection often requires support at an industrial facility.

Tank Designations are as follows: