Stress corrosion cracking initiation and short crack growth behaviour in Alloy 182 weld metal under simulated boiling water reactor hydrogen water chemistry conditions

Abstract

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.

Oxidation and SCC Initiation Studies of Type 304L SS in PWR Primary Water

“…Whilst it is recognised that the imposition of dynamic plastic straining is severe in the context of operating PWR plant, one of the immediate advantages is that the duration of the test is very short. Furthermore, recent work by Ritter et al [26,27] investigating the SCC initiation behavior of Alloy 182 showed that SSRT tests can provide results that are consistent with the outcomes obtained with more plant-relevant tests, such as constant load blunt notch compact tension (C(T)) tests. Most recently, Zhong et al [28] provided more evidence that SSRT can be used as an acceleration methodology to obtain results that are relevant to primary water SCC in nuclear power plant.…”

“…Results from tapered samples showed that cracks were observed in locations that were plastically strained by at least 2%. This threshold value for SCC is not, however, a universal value since it is expected that this threshold value would decrease at lower strain rates [26,27].…”

Stress corrosion crack initiation testing with tapered specimens in high-temperature water – results of a collaborative research project

“…Alloy 182 is more susceptible to SCC under HWC compared to NWC conditions. Here it must be noted that the hydrogen content for the BWR-HWC conditions was chosen in a way to end up at the Ni/NiO phase transition boundary, where other investigations have shown the highest SCC susceptibility of Alloy 182 [38]. Also, the effect of surface finish (ground versus polished) could be readily distinguished.…”

Electrochemical and spectroscopic characterization of oxide films formed on Alloy 182 in simulated boiling water reactor environment: Effect of dissolved hydrogen

“…In the following, the observed phenomenology and possible correlation with SCC mechanisms is discussed based on the obtained surface oxide film characteristics and SCC results from another study [15] and literature. As pointed out in the introduction, no single mechanism could fully explain all the SCC parameter effects, metallographic and fractographic observations.…”

“…This Ni/NiO phase boundary is predicted to decrease from 2.3 ppm DH at 360°C to 0.25 ppm DH at 274°C [13,14]. A recent initiation and growth study with Alloy 182 in simulated BWR environments showed that the maximum in crack initiation and growth is located at the Ni/NiO phase transition line [15]. Mechanistic studies of IGSCC in Ni-based alloys have increased in recent years and several mechanisms have been proposed such as slip-dissolution [16], selective internal oxidation [17], hydrogen assisted cracking/hydrogen embrittlement, and vacancy condensation [18].…”