4.5: CREVICE CORROSION

4.5 CREVICE CORROSION

This is a localized form of corrosion, caused by the deposition of dirt, dust, mud and deposits on a metallic surface or by the existence of voids, gaps and cavities between adjoining surfaces. An important condition is the formation of a differential aeration cell for crevice corrosion to occur. This phenomenon limits the use, particularly of steels, in marine environment, chemical and petrochemical industries.

4.5.1 CAUSES

Presence of narrow spaces between metal-tometal or non-metal to metal components.
Presence of cracks, cavities and other defects on metals.
Deposition of barnacles, biofouling organisms and similar deposits.
Deposition of dirt, mud or other deposits on a metal surface.

4.5.2 MATERIALS AND ENVIRONMENT

The conventional steels, like SS 304 and SS 316, can be subject to crevice corrosion in chloride containing environments, such as brackish water and seawater. Water chemistry plays a very important role.

Factors affecting crevice corrosion (Fig. 4.13):

Crevice type.
Alloy composition.
Passive film characteristics.
Geometry of crevice.
Bulk composition of media.
Bulk environment.
Mass transfer in and out of crevice.
Oxygen.

Crevice Type

Crevice type means whether the crevice is between metal-to-metal, metal to non-metal or a marine growth, like barnacles or other marine biofouling organisms, on the metal surface. It is important to know whether factors affecting crevice are man-made or natural in order to select appropriate methods for prevention.
Alloy Composition

It is important to know whether or not the alloy is resistant to crevice corrosion. For instance, work on the various grades of steels,...

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Principles of Corrosion Engineering and Corrosion Control

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4.5: CREVICE CORROSION