When there
are heterogeneities in the environment (such as waterline corrosion of
partially submerged objects due to an uneven oxygen distribution) or on
the material surface (such as distinct phases of a multiphase alloy),
localized corrosion occurs. Because of the electroneutrality criterion,
which states that every electron generated in the anodic process must be
consumed in the cathodic reaction, the reduction and oxidation reactions
must exist simultaneously with equal rate. Consequently, the
cathodic and anodic sites need to be electrically and electrolytically
connected in order for the circuit to be completed, as shown in the open
circuit potential, Fig. 0. Measuring the OCP (open circuit potential),
often called corrosion potential can predict the probability of corrosion
occurrence; OCP represents the measured potential of the electrode
without applied external current since it remains open (circuit not
closed)