Corrosion is the separation of an engineered material into its constituent atoms due to chemical reactions with its surroundings. It is the action wherein metal will transform to its original form of ore when it is interacted with water and oxygen. The process of changing from metal to a combined form is an anodic reaction. The most known example of corrosion is rusting which is caused by the formation of an oxide of iron due to the oxidation of the iron atoms in solid solution. Corrosion is caused by the following:

➢ Change in the ordinary potential in bimetallic couples.
➢ Difference in the metallurgical structure of the metal at various points on the outside.
➢ Changes in the environment such as the supply of air at the surface, wherein areas with strong winds becomes the cathode and those with little source of oxygen or air becomes the anode.

Yet, problems of corrosion are solved through a technique called Cathodic Protection (CP). Its principle is in connecting outside anode to the metal for protection and electricity is passed in order that the surface of the metal is cathodic therefore preventing corrosion. A sound cathodic protection design involves half cell (a structure that contains a conductive electrode and a surrounding conductive electrolyte) with test point all over the protected area.

There are two ways in achieving cathodic protection. It is either by using galvanic anodes (also called sacrificial anodes) or by using “impressed current”. Cathodic protection using galvanic anode systems uses reactive metals as secondary anodes and they are directly connected electrically to the steel to be protected. Commonly used metals as sacrificial anodes are aluminum, magnesium and zinc. They are alloyed metals are used and they are used to improve lasting performance and dissolution characteristics. Cathodic protection using impressed-current systems uses inactive anodes and uses an external source of dc power to impress a current from an external anode onto the cathode surface.