Fabrication of NDT Test Bodies with SCC Cracks in Alloy 182 Weld Metal and Their Metallographical Characterization

The current international PIONIC program (2018-2022) is dealing with the assessment, qualification and optimization of established and new emerging NDE techniques to detect and assess SCC flaws in dissimilar metal welds. PSI is participating in this program as sub-contractor of the Swiss Nuclear Safety Inspectorate (ENSI) by producing two NDE test bodies with realistic SCC cracks as in-kind contribution. The present report describes the generation of these NDE test bodies and reference SCC specimens from two test welds as well as the metallo- and fractogpaphical anaylsis of the crack paths and fracture morphologies and the qualification of the used approach. The NDE characterization will be described in a separate report by SVTI. Two rectangular NDT test bodies with shallow, semi-elliptical and planar interdendritic IGSCC cracks in the middle of the weld metal were fabricated from a nuclear grade Alloy 182-RPV steel dissimilar metal weld with little hot cracking. The SCC cracks were generated in oxygenated high-temperature water at 274 °C with the addition of 20 ppb of chloride with a final KI of 43 and 44 MPam1/2 that resulted in SCC growth rates in the range of 1 to 210-9 m/s and a 100 % intergranular engagement. The SCC cracks in the final test bodies have a thumbnail shape with no SCC growth at the side surfaces and with a maximum crack depth in the middle of the specimen of about 20 and 27 % of the wall thickness. The IGSCC cracks show the typical morphologies and characteristics of field SCC cracks and are thus a realistic simulation. After the detailed NDE characterization at SVTI, the test bodies can be used for further NDE investigations or the cracks could be extracted and inserted in more complex weld mock-ups with realistic geometries by minimal invasive welding techniques.