Dr. Dmitri Kopeliovich
Cathodic protection is the method of corrosion control, which provides suppression of the metal oxidation due to electrons flowing to the metal from an external source.
The external source of such electrons may be either DC power supply (impressed current cathodic protection) or sacrificial anode.
Impressed current cathodic protection is widely used for protection of large underground equipment (pipelines, storage tanks). Graphite, cast iron and some other materials are used as anodes for the impressed current cathodic protection. The anode is connected to the positive terminal of the power supply, the protected part is connected to the negative terminal. Such connection makes the protected part to work as a cathode. 50 V DC power supplies are commonly used in the method.
Cathodic protection by sacrificial anodes is used for protection water heaters, ship hulls, harbor structures, pier piles, subsea structures, offshore platforms, chemical processing equipment (tanks, pipes). Sacrificial anodes are made of magnesium, aluminum or zinc. A steel part has a higher value of electrode potential (more noble) than sacrificial anode therefore it works as a cathode in this galvanic cell.