Abstract
Stress corrosion cracking (SCC) is a potential risk in structural steels used for heat exchanger and circulation loop in LWR. Generally, SCC susceptibility of structural steels increases with increasing the level of dissolved oxygen (DO) in circulating water, but DO tolerance below which no SCC risk is present could differ by the type of steel. To investigate the DO effect on SCC susceptibility, T23, T24 and T91 steels under static load were exposed to stagnant and circulating water at 200°C with varying DO levels. The results indicated that among the tested steels, the SCC susceptibility was highest in T91 but lowest in T23 which did not exhibit crack initiation with 100 ppb DO. T24 showed no cracking with 50 ppb DO but cracked with 100 ppb DO, implying intermediate SCC susceptibility in between T23 and T91. Based on the cracking results and hardness data, SCC susceptibility in the tested steels is considered driven by corrosion which was initiated/affected by DO in the water.
