Crevice Corrosion of Stainless Steels: I. A Mathematical Model

Abstract

A mathematical model of the initiation stage of crevice corrosion has been developed, based on the generally accepted mechanism of oxygen depletion within the crevice, followed by a pH fall and eventually permanent breakdown of the passive film and the onset of rapid corrosion. The model highlights the importance of the critical crevice solution (CCS) and the current flowing when the alloy is in the passive condition (passive current), which characterise a given alloy's resistance to crevice corrosion, the crevice geometry and the Cl⁻ level of the bulk solution. The model predicts how the pH within the crevice falls with time until it reaches either the limiting value, as a result of mass transfer considerations, or the critical pH value which causes breakdown and the onset of rapid corrosion.

Potential uses of the model lie in the areas of materials selection, setting design criteria and defining environment limitationsfor the use of given alloys.