Pitting Corrosion

Pitting corrosion is a highly localised corrosive attack that forms tiny pits with a small surface area, but which can be quite deep.

Pitting occurs on non-ferrous metal when the protective passive film breaks down or has been weakened or damaged by contamination. When the break-through occurs in the passive film, the actively corroding pit constitutes the anode and the large passive film surrounding the pit acts as a cathodic surface.

The rate of dissolution of the metal is strongly influenced by the ratio between anode and cathode areas, consequently, the "driving force" behind the pitting attack can be very strong and deterioration can spread quickly.