Evaluation of the Maximum Pit Size Model on Stainless Steels under Thin Film Electrolyte Conditions

Abstract

This paper presents the experimental evaluation of a recently developed model for predicting the maximum pit size possible on a stainless steel surface under a certain set of atmospheric conditions. Prediction of the maximum pit size possible on 304L and 316L was accomplished by coupling the maximum cathode current available from a thin film of ferric chloride covering the steel's surface to the minimum current needed by a growing hemispherical pit. The experimental validation involved exposure tests of 304L and 316L steel samples covered by thin film of ferric chloride solution at a relative humidity of 97% with a loading density of 400 μg cm−2. Evaluation of the maximum pit size model was done by comparing the pit size from the model with the pit size obtained from exposure tests at the same atmospheric conditions. The model was found to bound all of the experimental data for both alloys if it was assumed that the critical pit solution was between 60% and 80% of the saturation concentration.