Welding Residual Stress Solutions for Dissimilar Metal Surge Line Nozzle Welds

At the end of 2006, defects were identified using ultrasonic testing in three of the pressurizer nozzle dissimilar metal (DM) welds at the Wolf Creek nuclear power plant. Understanding welding residual stress is important in the evaluation of why and how these defects occur, which in turn helps to determine the reliability of nuclear power plants. This paper presents analytical predictions of welding residual stress in the surge nozzle geometry identified at Wolf Creek. The analysis procedure in this paper includes not only the pass-by-pass welding steps, but also other essential fabrication steps of pressurizer surge nozzles. Detailed welding simulation analyses have been conducted to predict the magnitude of these stresses in the weld material. Case studies were carried out to investigate the change in the DM main weld stress fields resulting from different boundary conditions, material strength, weld sequencing, as well as simulation of the remaining piping system stiffness. A direct comparison of these analysis methodologies and results has been made in this paper. Weld residual stress results are compared directly to those calculated by the nuclear industry.