Stress Corrosion Cracking of Nickel Weld Metals in PWR Primary Water

This discussion reviews the occurrence of stress corrosion cracking (SCC) of Alloys 182 and 82 weld metals in primary water of pressurized water reactors (PWR) from both operating plants and laboratory experiments. Results from in-service experience show that more than 340 Alloy 182/82 welds have sustained SCC, and Alloy 182 with lower Cr have more failures than Alloy 82. Most of these cases have been attributed to the presence of high residual stresses produced during the manufacture aside from the inherent tendency for Alloy 182/82 to sustain SCC. The affected welds were not subjected to a stress relief heat treatment with adjacent low alloy steel components. Results from laboratory studies indicate that time-to-cracking of Alloy 82 (with Cr up to 18%–22%) was a factor of 4 to 10 longer than that for Alloy 182. SCC depends strongly on surface conditions, surface residual stresses and surface cold work, which are consistent with the results of in-service failures. Improvements in the resistance of advanced weld metals, Alloys 152 and 52, to SCC are discussed.