Analysis of environmentally assisted crack initiation of Alloy 182 in simulated light water reactor primary water with the engineering initiation model EngInit

Environmentally assisted cracking of nickel-base alloys has been observed in the primary coolant of light water reactors and is known as primary water stress corrosion cracking. In respect of crack growth, disposition curves are available for integrity analysis. However, in respect of initiation, there is no generally accepted approach. Here, a methodology is proposed to derive a usage factor towards initiation. Reaching a usage factor of 1 means that initiation is incipient. How far one is away from a usage factor of 1 tells us about the margin towards initiation. The key function in the approach is the rate at which the usage factor increases. It is proposed to be a function of strain rate and stress. Data from constant extension rate tests with flat, tapered tensile specimens have been used to parameterise the model. The parameterised model is subsequently used to predict initiation in a tensile-loaded, large-notch specimen.