Stability Considerations for Atmospheric Localized Corrosion

Corrosion resistant materials under atmospheric conditions can suffer from localized corrosion (e.g., pitting, crevice, stress-corrosion cracking). The stability of such a localized corrosion site requires that the site (anode) must dissolve at a sufficiently high rate to maintain the critical chemistry while a wetted surrounding area (cathode) provides matching cathodic current.  The objective of this study was to computationally characterize the stability of such a local corrosion site and explore the effects of physiochemical parameters and electrochemical kinetics. An analytical method for evaluating the stability of localized corrosion of corrosion-resistant alloys under thin-layer (or atmospheric) conditions is presented.  The method uses input data that are either thermodynamic in nature or easily obtained experimentally.  The maximum cathode current available depends on the cathode geometry, temperature, relative humidity, deposition density of salt (i.e., mass of salt per unit area of cathode), and the interfacial electrochemical kinetics.  The anode demand depends on the localized corrosion site geometry and the localized corrosion stability product.  By coupling these two approaches, the stability of a crevice can be determined for a given environmental scenario.  The method has been applied to the atmospheric localized corrosion of Type 316L stainless steel.