Predicting Stress Corrosion Crack Tip Electrochemical Conditions and the Influence of Exposure Environment

Abstract

Metallic structures are commonly exposed to marine atmospheric conditions in real world conditions, characterized by thin water layers (WL) allowing for corrosion to occur. For austenitic stainless steels in such atmospheric environments, pitting and stress corrosion cracking (SCC) are potential degradation mechanisms. The rate and extent of corrosion and SCC on the alloy surface is dictated by the combination of environmental, physicochemical, and geometric variables, which include relative humidity, temperature, electrolyte conductivity, electrolyte film thickness, in addition to the electrochemical kinetics on the alloy surface. Due to the large potential variation in environmental conditions, modeling can serve as an important tool to evaluate environmental effects on the corrosion and SCC of alloys and galvanic couples.In this study, Finite Element Modeling approaches are used to evaluate chemical and electrochemical conditions present in a crack exposed to marine, thin film environments. A full reactive transport model, incorporating metal hydrolysis and salt formation, is built to evaluate SCC crack tip conditions. The influence of WL thickness, stress intensity level, crack length, and specimen geometry are evaluated. Specifically, crack tip pH and equilibrium potential among other variables will be compared between the various atmospheric factors both spatially and temporally. The modeling results will be compared to atmospheric SCC experiments and help give insight into critical experimental and testing phenomena. Acknowledgements Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This document is SAND2021-5051 A.