The Role of Inclusions on Initiation of Crevice Corrosion of Stainless Steel: II . Theoretical Studies

A mathematical model for the initiation of crevice corrosion on 304 stainless steel in was developed. The central concept is that thiosulfate ions, formed by dissolution of inclusions and trapped within the crevice, act in concert with chloride ions to cause passivity breakdown when their concentrations exceed critical values. The model includes consideration of migration and diffusion of the supporting electrolyte, as well as ions produced by dissolution of metal and inclusions. Experimental data reported separately in Part I were compared with theoretical predictions for the critical geometry at which initiation occurred, and for the degree of cathodic protection required to prevent crevice corrosion. A simplified model was developed to predict conditions under which breakdown would be expected to occur for various cases of crevice geometry, potential at the edge of the crevice, and inclusion density.