Residual Stress Measurements in Dissimilar Metal Welds

Pressurized water nuclear power reactor piping system dissimilar metal (DM) welds (carbon steel/Inconel/stainless steel) are susceptible to Primary Water Stress Corrosion Cracking (PWSCC) as an active degradation mechanism. PWSCC is highly influenced by the state of stress within the susceptible material, and tensile residual stresses in DM welds are an established driving force for PWSCC. Hence, proper predictions and measurements of such stresses are essential to accurately assess the nuclear power industry's flaw evaluations and crack growth assessments. Recent improvements in computational efficiency have facilitated advances in weld residual stress modeling.

This project will characterize welding residual stresses in pressurized water reactor plant components using the contour and slitting measurement techniques. These strain relief based methods provide point-to-point variability in residual stresses for weld cross sections, repair weld locations and at fabrication flaws. Variation in weld residual stress is of regulatory importance as it is a required input to probabilistic risk assessments codes for component leak-before-break evaluation (for example the extremely-low probability of rupture (xLPR) code in development by the Office of Nuclear Regulatory Research (RES)).

Residual Stress Measurements in High Density Polyethylene Piping

Fitness for service requirements for safety related High Density Polyethylene Piping (HDPE) systems are currently being developed by the nuclear power industry in the ASME Code. Residual stresses resulting from fabrication and joining potentially affect the flaw tolerance of the HDPE material. As confirmatory research of the industry's HDPE initiatives, a series of slitting and contour measurements would provide the magnitude of residual stresses in as-fabricated and joined HDPE piping for nuclear application. A joined section of HDPE material is available for characterization, fabricated as part of NRC programs at Pacific Northwest National Laboratory.

The two main objectives for this project are to:

1. Characterize DM welding residual stresses in nuclear reactor component DM welds using contour and slitting methods.

2. Characterize fabrication and joining residual stresses in High Density Polyethylene Piping using contour and slitting methods.