Surface Conditions Leading to Localized Corrosion

Localized corrosion can be related to the microstructure of a metal or alloy, the physical condition of the surface, or coupling of the metal to a dissimilar metal or to conducting surface films, usually oxides. These conditions are listed in an order generally observed to be increasingly conducive to localized attack leading to failure. 

In all of these conditions, important variables are the cathode-to-an-ode area ratio, Ac/Aa, and the ability of the cathodic surfaces to support cathodic reactions and thereby enhance the corrosion of anodic sites. 

Environmental conditions leading to localized corrosion are usually associated with nonuniform concentrations of cathodic reactant species or corrosion product ions. These conditions can be brought about by the following  

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