Crevice corrosion may occur when something, i.e., a crevice former, blocks the surface of the stainless steel and prevents oxygen from renewing the passive film. The crevice former can be almost anything that prevents the air from reaching the surface. It m
ay be deposits from the process, dirt, gaskets, weld spatter, or coatings or paint marking. The likelihood of crevice attack increases as the crevice becomes tighter, e.g. a metal-on-metal or gasket-on-metal joint, or a barnacle on the steel surface, and if the process environment has high chlorides, low pH, or high temperatures. The solution is similar to that for pitting corrosion - stainless steels with increased levels of Cr, Mo, and N have increased resistance to crevice corrosion.
