The effect of dissolved hydrogen on the stress corrosion cracking initiation and short crack growth behaviour of Alloy 182 weld metal was evaluated in 274 °C hydrogenated high-purity water using accelerated crack initiation and growth tests with sharply notched fracture mechanics specimens and in-situ crack initiation and growth monitoring. A maximum in initiation susceptibility and crack growth rates was observed at the Ni/NiO phase transition line. Grain boundary misorientations and mismatch in Schmid factor were measured by electron backscattered diffraction along intergranular stress corrosion cracks and at crack initiation sites. Low angle boundaries seem to be particularly resistant to cracking.

The influence of dissolved hydrogen content and surface finish on the stress corrosion cracking (SCC) initiation behaviour in Alloy 182 weld metal was studied with flat tapered tensile specimens in simulated boiling water reactor water at 274°C using constant extension rate tensile tests. The surface crack distribution, crack depth and stress threshold for SCC initiation were analysed by detailed post-test quantitative characterisation. Intergranular SCC initiation has been found in all specimens tested with dissolved hydrogen contents varying from 10 to 2000 ppb. The highest crack density and depth and lowest stress threshold for crack initiation were found to be at the Ni/NiO phase transition line with 253 ppb dissolved hydrogen content. In addition, ground surfaces showed a tendency to higher SCC initiation susceptibility compared to electropolished surfaces.

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In boiling water reactor (BWR) environments, the content of dissolved hydrogen (DH) in the high-temperature water has an influence on the stress corrosion cracking (SCC) susceptibility of Ni-based alloys. In order to understand the possible role of different types of surface oxide films in the SCC initiation process, oxide films formed on Alloy 182 weld metal under simulated BWR conditions at 274°C with varying contents of DH from 10 to 2200 ppb, were investigated by electrochemical and spectroscopic methods. The influence of the DH content on the nature of the oxide films is discussed in the context of SCC mechanisms.

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