Corrosion Current

The magnitude of corrosion is directly related to the corrosion current which is generated by the corrosion cell. The magnitude of corrosion current is I = E/R, where E is the potential in volts, R is the resistance in ohms, and I is the current in amperes. The larger the potential, the greater is the corrosion current.

The corrosion current flow in a corrosion cell is shown below. 

Combined Anodic and Cathodic Reactions

Figure below shows the combined anodic and cathodic reactions. 

Oxidation occurs only at the anodic sites and reduction at cathodic sites. If the anodic sites are eliminated, corrosion is eliminated. This is what is done in Cathodic Protection. Anodic reaction is eliminated and only cathodic reaction is made to occur.