Residual Stress Stresses in Dissimilar Metal Welds for Nuclear Applications

Reactor pressure vessels and piping systems typically contain welded joints. In many cases these welded joints are large, contain significant amounts of residual stress, have reduced material properties (e.g., stress corrosion cracking resistance, fracture toughness), and contain defects. For these and other reasons, the welded joints tend to be critical locations in terms of the design and sustainment of these systems. In pressurized water reactor coolant systems, nickel based dissimilar metal (DM) welds are typically used to join carbon steel components, including the reactor pressure vessel to stainless steel piping. Fleet experience shows the DM welds to be susceptible to primary water stress corrosion cracking (PWSCC), and the residual stresses have a significant influence on the likelihood of PWSCC crack initiation and the rates of crack growth. Despite their importance, only limited data on the residual stress fields near DM welds exist, and industry-standard safety cases are based upon conservative residual stress assumptions. Improved understanding of DM weld residual stress fields would help the industry to more optimally manage sustainment of the existing reactor fleet and improve future designs.