Effect of stress on passivation kinetics and passivation modelling of 304L stainless steel in acidic medium

Abstract

Stress Corrosion Cracking (SCC) is a typical failure of engineering materials applied in corrosive environments. In light water reactors for example, this results in loss of electrical capacity and related costs of repair and replacement. Film Rupture-dissolution Model explains interganular SCC as a phenomenon resulting from repetitive activation/passivation cycles (Fig.1). Activation takes place mechanically by slip-induced film breakdown which causes excessive material dissolution until it repassivates again. In this study, potentiodynamic cycling experiments serve effectively to perform in-Lab electrochemical simulation of this process. Conventional electrochemical techniques and Inductively Coupled Plasma – Optical Emission Spectroscopy are used to in-situ measure the corrosion transients and dissolution rates. A model was developed proving that stainless steel repassivates according to the High Field Ion Conduction Model in acidic solutions. Having this, quantification of the instantaneous passive film thickness and corrosion susceptibility of the passive film constructed over the surface has been successfully achieved (Fig.2). Quantified results showed that for stressed materials, the time to repassivation is longer, and the constructed passive film, though thicker, is more susceptible to corrosion than passive films developed over non-stressed materials.