Crevice Corrosion
DESCRIPTION
Crevice corrosion is localized corrosion which may occur in
small areas of stagnant solution in crevices, joints and under
corrosion deposits (i.e. under deposit corrosion).
PREVENTION OR REMEDIAL ACTION
- redesign of equipment to eliminate crevices.
- close crevices with non-absorbent materials or
incorporate a barrier to prevent of moisture penetration
into crevice.
- prevent or remove builds-up of scale or other solids on
surface of material.
- use of one-piece or welded construction versus bolting or
riveting.
- select more corrosion resistant or inert alloy (note: see
pitting corrosion for more information).
STANDARD TEST METHODS
- ASTM G-48 - test methods for pitting and crevice
corrosion resistance of stainless steels and related
alloys by the use of ferric chloride solution.
- ASTM G-78 - guide for crevice corrosion testing of
iron-base and nickel-base stainless alloys in sea water
and other chloride-containing aqueous media.
Evaluation of Crevice Corrosion
The principal reference for the evaluation of crevice
corrosion is ASTM G78. The extent of crevice corrosion can be
greatly influenced by the nature of the crevice and the technique
utilized in the exposure test. Typically, tighter crevices
promote greater localized corrosive attack. The use of serrated
TFE or ceramic washers is one of the most common methods for
obtaining reproducible simulation of crevice corrosion. These
washers are bolted to the specimen using a corrosion resistant
bolt with constant applied torque for each crevice washer
assembly. In most cases, the rate of crevice attack in not
constant. Initially, there is an incubation period where the
attack rate is essentially zero. However, as the corrosivity of
the crevice environment increases with exposure time, the local
attack rate can actually increase with time in test. Therefore,
multiple exposure periods may be needed to accurately assess
crevice corrosion attack rates.
