The Use of Tapered Specimens to Evaluate the SCC Initiation Susceptibility in Alloy 182 in BWR and PWR Environments

摘要

A better understanding of stress corrosion cracking (SCC) initiation is one of the keys towards developing proactive mitigation techniques for the safe and economic operation of nuclear power plants. However, SCC initiation laboratory studies are very time consuming and require multiple specimens, Hence, in the framework of the European "MICRIN+" research project, an accelerated test method was evaluated for screening the SCC susceptibility in a relatively short time frame. The effects of surface roughness and strain rate on SCC initiation susceptibility in Alloy 182 weld metal were evaluated in simulated BWR and PWR environments. Constant extension rate tensile tests were performed using flat tapered tensile specimens with different surface finishes (ground and polished) in hydrogenated water at 288 and 340 °C. The surface crack distribution and crack length as well as stress thresholds for SCC initiation were analyzed by detailed post-test quantitative characterization. Some test data were analyzed by the EngInit SCC initiation model. The accelerated test technique was successfully applied and revealed very promising results. The highest crack density and lowest stress thresholds for crack initiation were found on the ground surfaces and at the lowest strain rates. A test's load response can be fed to the EngInit model; with parameters to be determined by comparing EngInit's damage to the experimental surface crack distributions. Englnit can potentially be used to link laboratory test results on flat tapered specimens to SCC initiation in components in the field.