Corrosion handbook

8 06/21

1.2.3 Crevice corrosion

Crevice corrosion refers to corrosion occurring in cracks or crevices formed

between two surfaces (made from the same metal, different metals or even

a metal and a non-metal). This type of corrosion is initiated by the restricted

entrance of oxygen from the air. The access of oxygen into the crevice area is

hindered, whereby the cathodic partial reaction (see 1.1) preferably takes place

only outside the crevice. The crevice area itself becomes the anode, and thus the

preferred region for metal dissolution. (see Fig. 7).

It may also occur under washers or gaskets, when the entry of water underneath

is not prevented (see Fig. 7).

There are lower and upper limits to the size of a crevice in which corrosion

may be induced. If the crevice is too tight, no electrolyte for corrosion will be

introduced. If the crevice is too wide to reduce oxygen entrance, the aeration cell

and consequently different concentrations of oxygen cannot develop. However,

the critical crevice width depends on several factors such as the type of metals

involved, the corroding environment and the wet/dry cycles.

0RUHQREOH /HVVQREOH

Oxygen rich

Oxygen starved

Fig. 7: Possible areas for crevice corrosion in a fastening structure.