WATERLINE CORROSION

• Waterline corrosion is also known as marine corrosion.• Waterline corrosion is occurs when metal touches to the water surface

such as floating ships, water storage steel tanks etc. in which a portion of a metal always under water.

• Corrosion by water is an electrochemical process, whenever a metal or alloy come in contact with water always have a specific electrical potential at specific water level.

MECHANISM• Waterline corrosion takes place due to the formation of differential

oxygen concentration cell.• The part of the metal below the waterline is exposed only to dissolved

oxygen while the part above the water is exposed to the higher oxygen concentration of the atmosphere.

• Thus, part of the metal below the waterline is act as an anode and undergoes corrosion and part above the waterline act as cathode and free from corrosion.

• A ship is floating on water surface, the base surface of ship is exposed to dissolved oxygen act as anode and undergoes corrosion.

• While, the upper surface is exposed to higher oxygen concentration act as cathode and protected from corrosion.

PREVENTIONS• Coating and lining• Insulation• Sacrificial metal• Corrosion inhibitor

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