Modeling the Effects of Dissolved Hydrogen, Temperature, pH, and Global Stress on Stress Corrosion Cracking of a Cr-Ni Model Alloy in High-Temperature Water

Abstract

As an extension of recently presented SCC models for pure nickel and iron in high temperature water, the anodic path -hydrogen assisted stress corrosion cracking of a Cr-Ni alloy is presented simulating alloy 600 properties. With the local anodic path corrosion as the crack initiation phase, the respective oxides precipitate while the crack tip solution will acidify and establish local hydrogen ion reduction conditions. Depending on the applied global stress, local plastic straining will then provide an active crack tip surface that transfers atomic hydrogen to the plastic zone ahead of the crack tip.Hydrogen assisted crack propagation is then controlled by the calculated local hydrogen ion reduction charge and the plastic strain distribution ahead of the crack tip. The resultsshow that for global stress levels close to the yield stress and at constant dissolved oxygen contents the increasing dissolved hydrogen contents are providing peak crack growth rates at hydrogen levels that decrease both with increasing temperatures and bulk pH. The peak crack growth rates decrease also with decreasing global stress as well as with increasing temperature and increasing bulk pH. The results are in accordance with published experimental investigations and operational experiences regarding the effects of dissolved hydrogen on stress corrosion rates in high temperature waters of nuclear reactors. They are explained by the interaction between the electrochemical parameters of the respective reactions.