Part Repair and Start/Stop Effects and Three Dimensional Residual Stress in Dissimilar Metal Welds

PWR nuclear power plants have dissimilar metal (DM) welds at many junctions between the vessels and the piping. The DM welds are made with Alloy 82 filler materials between carbon steel and stainless steel. These are potentially susceptible to Primary Water Stress Corrosion Cracking (PWSCC). PWSCC is mainly driven by the tensile weld residual stresses (WRS) that develop during fabrication of the piping system. In particular, weld repairs that often occur during the weld fabrication process also play a strong role in the development of the weld residual stress state in and near the DM welds. Most weld residual stress analyses performed to date in order to characterize the weld residual stress state in DM welds for PWSCC crack growth, leakage, and subsequent failure used axis-symmetric assessments. The purpose of this work is to provide direct assessment of the appropriateness of this axis-symmetric assumption on the WRS by comparison with full three dimensional analyses of several nozzles. In particular, weld start stop effects on the original weld will be assessed. In addition, the effect of partial arc weld repairs will be included. Repair cases considered include 15% and 50% deep repairs of length 48-degree and 96-degree of the circumference, along with the baseline case with no repair. The more complex three dimensional WRS state from the three dimensional analyses are compared to the corresponding axis-symmetric solutions and guidelines regarding the appropriateness of 2D solutions are discussed. Finally, some limited calculations of stress intensity factors at locations along the repair are presented.