Weld Heat Input and Stress Corrosion Cracking of Alloy 182 Filler in a Pressurized Water Reactor Nuclear Reactor Coolant Environment

In pressurized water reactors (PWR), dissimilar metal welds are made to join the pressure vessels of low-alloy steel to pipes of stainless steel using Alloy 182 (UNS W86182) as a filler metal. However, it has been found that Alloy 182 is susceptible to intergranular environmentally assisted cracking (IGEAC) at high temperatures, and this has been one of the major concerns in the management and prediction of plant life. Variation within welds and welders are expected; for design and integrity assessment of the dissimilar welds, these variations should be evaluated. In this study, three dissimilar welds blocks of ASTM A508 steel were prepared using gas tungsten arc welding (GTAW; buttering) and shield metal arc welding (SMAW) processes using Alloys 82/182 (UNS N06082/UNS W86182) as filler metal. Three different welding conditions or heat inputs were used: normal or conventional for the procedure, higher, and normal but cooled. Samples were taken from the three blocks and tested with slow strain rate testing (SSRT). All specimens were taken from the region filled by Alloy 182 within the dissimilar welded blocks and tested under the PWR environment. Microstructures were observed under optical and electron microscopes. Typical dendrite structures were observed in Alloys 82/182 welds. Microhardness tests were conducted to measure the variation in hardness of the weld. It was discovered that a higher heat input increases the ASTM G129 ratios that shall be utilized in evaluating SSRT.