Effect of hydrogenated low temperature water on fracture toughness of nickel based weld metals

Nickel-based alloys are susceptible to a form of hydrogen embrittlement, Low Temperature Crack Propagation (LTCP), which can cause severe degradation of the fracture resistance of nickel-based alloys. LTCP may occur in low temperature water, with the highest susceptibility reported at about 55 C, with high stress and slow loading rate in pre-cracked Ni-based materials. Although LTCP has not been reported in commercial reactors, the susceptibility of different alloys is important to establish. As a part of the Finnish Reactor Safety Program, SAFIR 2010, the effect of hydrogenated Pressurized Water Reactor, PWR, primary water on the LTCP susceptibility of nickel-based weld metals of Alloy 182, 82, 152 and 52 was studied performing J-R-tests at a slow displacement rate in simulated low temperature PWR primary water. The results revealed that Alloy 182 is the most susceptible nickel-based weld metal to LTCP. Pure weld metal specimens were substantially more susceptible to LTCP than the dissimilar metal weld specimens. Pre-exposure to high temperature hydrogenated water did not affect remarkably the fracture toughness of any of the test materials.