Crevice corrosion
Crevice corrosion refers to corrosion occurring in confined spaces to which the access of the working fluid from the environment is limited. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.
This photo shows that corrosion occurred in the crevice between the tube and tube sheet (both made of type 316 stainless steel) of a heat exchanger in a sea water desalination plant.
Mechanism