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

• Published in: Corrosion (Houston, Tex.) Tex.), 2015-05, Vol.71 (5), p.559-573
• Main Authors: Hoffmeister, Hans, Böllinghaus, Thomas
• Format: Article
• Language: English
• Subjects: Acidification; Alloys; Chemical reactions; Chromium nickel alloys; Corrosion; Corrosion effects; Corrosion potential; Corrosion rate; Crack initiation; Crack propagation; Crack tips; Cracking (corrosion); Cracks; Dissolution; Dissolved oxygen; Electrochemistry; Electrodes; Growth rate; Heat resistant alloys; High temperature; Hydrogen; Hydrogen ions; Hydrogen reduction; Hydrogen storage; Hydrologic cycle; Ion charge; Mathematical models; Mechanical properties; Nickel; Nickel alloys; Nuclear power plants; Nuclear reactors; Oxides; pH effects; Plastic deformation; Plastic zones; Plastics; Propagation; Reduction; Strain distribution; Stress corrosion; Stress corrosion cracking; Stresses; Temperature; Water temperature; Yield stress
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1443

As an extension of recently presented stress corrosion cracking (SCC) models for pure nickel and iron in high-temperature water, the anodic path, hydrogen-assisted stress corrosion cracking of a model Cr-Ni alloy is presented, utilizing Alloy 600 (UNS 06600) mechanical properties. With the local anodic path corrosion as the crack initiation phase, the respective oxides precipitate while the crack tip solution acidify and establish local hydrogen ion reduction conditions. Depending on the applied global stress, local plastic straining then provides 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 results show that for global stress levels close to the yield stress and at constant dissolved oxygen contents, the increasing dissolved hydrogen contents provide peak crack growth rates at hydrogen levels that decrease both with increasing temperatures and bulk pH. The peak crack growth rates also decrease 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.