Effect of dissolved hydrogen on the crack growth rate and oxide film formation at the crack tip of alloy 600 exposed to simulated PWR primary water

Abstract

The effect of dissolved hydrogen (DH) on primary water stress corrosion cracking of nickel base alloys has been of intense interest for plant operators worldwide. In this study, crack growth rates of Alloy 600 were measured in simulated PWR primary coolant at 330 °C with DH levels of 5, 16, 45 and 75 cc H 2 /kg H 2 O, respectively. The oxide films formed in the crack tip regions were examined using transmission electron microscopy (TEM). The results show low and similar crack growth rates at all DH levels, without a maximum at 16 cc H 2 /kg H 2 O. The low DH content favors nickel oxide formation at the crack tip region, whereas the high DH level favors Me 3 O 4 type spinel formation. Also, the oxide films were found to grow epitaxially on some metal grain surfaces in the cracks. The possible effects of alloy composition on the oxide films formed, and the effect of DH on the crack growth are briefly discussed.