Passivity breakdown mechanism stainless steel

Some SRB may cause loealized corrosion on stainless steels, nickel alloys, aluminium, zinc and copper alloys. Mechanisms of sulphur-assisted corrosion, with emphasis on Fe- and Ni-based materials, have recently been reviewed by Marcus [6.17]. The review includes the fundamentals of enhanced dissolution, retarding or blocking of passivation, and passivity breakdown. 

An outstanding contribution has been made by Oldfield and Sutton [13]. They have developed a mathematical model of crevice corrosion in which observations, such as the fall in pH, localized breakdown of passive films and the onset of crevice corrosion in stainless steels, is presented. A summary of the model developed by Oldfield and Sutton is given below. For calculation and detailed discussion, reference must be made to the original paper. In the model developed, crevice corrosion is considered a four stage mechanism. The four stages of crevice corrosion suggested are shown in Fig. 4.18. 

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