MITIGATION EFFECT OF HYDROGEN WATER CHEMISTRY ON STRESS CORROSION AND LOW-FREQUENCY CORROSION FATIGUE CRACK GROWTH IN LOW-ALLOY STEELS

摘要

The mitigation effect of hydrogen water chemistry (HWC) on the stress corrosion cracking (SCC) and low-frequency corrosion fatigue (CF) crack growth behaviour of low-alloy reactor pressure vessel (RPV) steels was investigated under boiling water reactor (BWR) conditions. The special emphasis was placed to those critical parameter combinations, which revealed accelerated SCC and CF crack growth well above the BWRVIP-60 SCC disposition lines and ASME XI reference fatigue crack growth curves under normal water chemistry (NWC) conditions in previous studies. For this reason, the SCC and CF crack growth behaviour of different RPV steels and weld filler/weld heat-affected zone materials in oxygenated (NWC) or hydrogenated (HWC) high-temperature water was characterized by cyclic and constant load tests with pre-cracked fracture mechanics specimens. The application of HWC always resulted in a significant reduction of SCC and low-frequency CF crack growth rates (CGR) by at least one order of magnitude with respect to NWC conditions. A few hours after changing from oxidizing NWC to reducing HWC conditions, the CGR generally dropped below the corresponding disposition curves. HWC is therefore a promising and powerful mitigation method for EAC in low-alloy steels under these critical parameter combinations.