Cathodic Protection

Electrochemical Corrosion is one of the types of corrosion in metals.  Electrochemical corrosion occurs, chiefly, in submerged metallic structures such as pipelines, storage tanks, water circulating systems, ship hulls and off shore platforms.  Electrochemical Corrosion occurs when the potential on the surface of the metal is not uniform.  

This uneven potential on the surface is caused due to impurities in the surface or uneven stress on the surface of metals.  This causes certain parts of the surface to act as an anode while other parts of the surface act like the cathode.  The current which flows between the anodic and the cathodic regions can cause corrosion.

Cathodic protection refers to a method of protection of these metallic structures from electrochemical corrosion.  This is achieved by making the metal to be protected the cathode.  When a material which has a higher electrode potential is kept in the same medium as the object to be protected, it becomes the cathode while the object to be protected becomes the cathode.  A simple electrochemical cell is created.  The electrons move from the anode to the cathode in the medium.  In the process, the anode gets corroded while the cathode is protected from corrosion.  The anode used is called the sacrificial anode. 

The sacrificial anode has to be periodically replaced as it gets eaten away.