Criteria for the unstable failure of cracked stainless steel piping

The intergranular stress corrosion cracking (IGSCC) of Type 304 stainless steel piping systems in Boiling Water Reactors has posed some very interesting and challenging problems related to the growth of cracks in ductile materials. The stress corrosion cracks have been found in the heat-affected zones of girth welds and they form at the inner surface of a pipe; the cracks are oriented circumferentially and are able to grow slowly in service by an environmentally assisted mechanism. From a safety perspective, an important issue is whether accident loadings will convert, by a non-environmentally assisted mechanism, i.e. a plastic fracture mechanism, a part-through stress corrosion crack into a through-wall crack, which will then spread around the pipe circumference and so cause complete pipe severance (guillotine rupture).