SCC BEHAVIOR OF ALLOY 52M/182 WELD OVERLAY IN A PWR ENVIRONMENT

Weld overlays (WOL) of alloys believed to possess superior stress corrosion cracking (SCC) resistance are typically applied over welds made with SCC-susceptible alloys with the expectation that they will act as a barrier to SCC. The objective of this work is to investigate the behavior of a crack initiated in Alloy 182 as it approaches the Alloy 52M WOL interface. For this purpose, an Alloy 52M WOL was deposited on a double-J Alloy 182 weld. Compact tension specimens were fabricated with the notch in Alloy 182 and oriented towards the WOL, and tested in a simulated PWR environment. The first such test revealed that the SCC rates in Alloy 182 were found to decrease by an order of magnitude ahead of the interface, and that the crack advanced from Alloy 182 into Alloy 52M. The post test examination found that crack branching occurred at the interface between the two alloys. Growth in Alloy 52M along the interface appears severe, approx. 10(-10) m/s. While for the most part (70%) the crack propagated along the interface, SCC cracking was also found to extend into Alloy 52M along the original direction. This cracking is substantial, yielding SCC rates of 10(-11) m/s.