Further Welding Residual Stress and Flaw Tolerance Assessment of Dissimilar Metal Welds With Alloy 52 Inlays

Primary water stress corrosion cracking (PWSCC) in nickel-based dissimilar metal (DM) welds (specifically Alloy 82/182 welds) in pressurized water reactors (PWRs) can cause a safety concern due to the high crack growth rate and irregular shaped flaws. Since many of these welds reside in primary piping systems that have been approved for Leak-Before-Break (LBB), the domestic commercial nuclear power industry has proposed a number of mitigation strategies for dealing with the issue and assuring LBB is still applicable. Some of these methods include Mechanical Stress Improvement Process (MSIP), Full and Optimized Structural Weld Overlay (FSWOL, OWOL), and Inlay and Onlay cladding. The industry claims that these methods provide either a reduction in the inner diameter residual stress field (MSIP and WOL), and/or apply a non-susceptible corrosion resistant barrier to stop or retard PWSCC crack growth to form a through-wall leak path (WOL, Inlay, Onlay). At last years PVP conference, a companion paper was published that described the initial welding residual stress and flaw evaluation analyses to investigate the effectiveness of inlay welds as a mitigative technique. The results from that effort suggested that the time to leakage with an inlayed weld is highly affected by the depth of the inlay and the crack growth rate within the inlay. In this ongoing effort, further welding residual stress analyses are presented that investigate the effects of the inlay depth and a variety of weld repair options before the standard 3mm deep inlay. In addition, further crack growth analyses, assuming idealized crack shapes, were conducted to investigate the effects of weld residual stress, crack growth rate, global bending stress, and flaw size and orientation. The results of these analyses aid in determining appropriate inspection intervals for dissimilar metal welds with this mitigation technique.