Abstract
Crack growth rate (CGR) measurement is an important tool to understand the behaviors of the environmentally assisted cracking (EAC) of various materials used in light water reactor (LWR) environments. In addition, such measurements are also used to produce quantitative data on corrosion fatigue (CF) and stress corrosion cracking (SCC). This type of data is essential for structural integrity analyses, as well as for the lifetime estimation and reliability of existing or postulated defects.In this paper, behaviors of CF and SCC experiments with two different nuclear grade reactor pressure vessel (RPV) low-alloy steels (LAS) with low- (A508 Cl.2, 0.008 wt.%) or high-sulfur (A533B Cl.1, 0.018 wt.%) steel content at 288°C under simulated boiling water reactor (BWR) conditions are presented. CGR of RPV LAS was found to be dependent upon various mechanical factors such as the stress intensity factor range (?K), loading frequency (ν), rise time (ΔtR), and hold time (ΔtH) at maximum load. In CF tests, it was observed that the CGR increased as ?K increased under the same water quality and loading conditions. If ?K was similar, the higher the ν (or the shorter ΔtR), the higher was the CGR. In SCC tests, the longer the ΔtH, the slower the CGR was under periodic partial unloading (PPU) conditions.On the other hand, it was found that dissolved hydrogen (DH), which lowered the electrochemical potential (ECP), could effectively suppress the CGR in either CF or SCC tests. The mechanism of the suppressive effect of DH on the CGR and the water chemistry conditions near the crack tip was also discussed in this paper. And, effect of steel sulfur content on CGR was less pronounced under low-frequency loading (e.g., ν ? 4×10-3 Hz) and low-flow, oxidizing (e.g., ECP = 100-200mVSHE) BWR/normal water chemistry (NWC) conditions.After mean crack lengths of various test specimens were evaluated using a specific electrochemical oxide removal method (ENDOX treatment), many CGR data from this study were observed to be comparable with those obtained from some well-known CGR prediction models for BWR environments except in the hydrogen water chemistry (HWC) condition. However, the current CF CGR data with a low loading frequency (ν = 4×10-4 Hz) were not bounded by the model developed by Eason. Additionally, most of our SCC CGR data cannot be encompassed by the MPA Stuttgart models.