Corrosion that starts in shielded gaps a fraction of a millimetre wide: flange faces under gaskets, threads, lap joints, under washers, barnacles or sediment. Oxygen inside the crevice is used up, the trapped solution turns acidic and chloride-rich, and the crevice becomes an anode coupled to the open surface outside. Passive alloys such as stainless steels are most vulnerable, and crevice attack starts at lower temperatures than pitting in the same alloy.
Pulled the flange and there's crevice corrosion right under the gasket, 316 does not like this seawater.
In seawater, stainless usually fails at gaskets and threads long before open surfaces pit, so design out crevices before paying for a better alloy.
Also heard as
- concentration cell corrosion
- gasket face corrosion
Related terms
Pitting
Localized corrosion that drills small, deep cavities into metal while the surface around them stays nearly intact.
PREN
Pitting resistance equivalent number: an index of a stainless alloy's chloride pitting resistance from its chemistry.
Tuberculation
Growth of knob-like mounds of rust and deposits on the inside of iron and steel water pipes.
Rust jacking
Swelling of rust between steel parts that pries joints apart, bows plates and pops rivets.