2016 年 15 巻 1 号 p. 21-31
A stress corrosion cracking (SCC) test was conducted using reverse U-bend specimens of MA alloy 600 and the uniaxial constant load test technique for alloy X-750 in simulated or modified PWR primary water under dissolved hydrogen (DH) of 5, 15 and 30 ml/kg at 290℃ and 320℃ because there is very little data from SCC initiation tests (particularly at 290℃) worldwide. It is well known that the SCC in primary water (PWSCC) growth rate for a Ni-based alloy shows a peak depending on the DH concentration due to the chemical stability of Ni and NiO. On the other hand, the dependence on DH is not clear for the PWSCC initiation time. It was anticipated that the PWSCC initiation time under DH of 5 ml/kg at 290℃ would be longer (better) than that at a higher DH concentration according to previous literature data. However, this study showed the shortest PWSCC initiation time under DH of 5 ml/kg at 290℃; thus, it matched the dependence on DH of the PWSCC growth rate. These results were considered to be due to the high stress applied to the specimens.
