All metals and alloys undergo a natural corrosion. The extent of corrosion depends on the nature of the alloy and the environment in which it is placed. The seas are one of the most corrosive of environments. Protecting steel structures from corrosion in marine conditions is therefore a challenging task. The consequences of corrosion in structures such as ship hulls, underwater piles of wharves and jetties, underwater pipes carrying oil or the various complex underwater structures in a oil rig are so catastrophic that all these structures have to be protected through cathodic protection even if they have protective coatings. Pipelines and structures buried under soil also need similar protection.

There are two broad methods of Cathodic Protection