Conservatism of ASME K-reference curve with respect to crack arrest

The conservatism of the RT temperature indexing parameter and the ASME A-reference curve with respect to crack arrest toughness, has been evaluated. Based on an analysis of the original ASME K data, it was established that inherently, the ASME K-reference curve corresponds to an overall 5% lower bound curve with respect to crack arrest. It was shown that the scatter of crack arrest toughness is essentially material independent and has a standard deviation (S.D.) of 18% and the temperature dependence of K has the same form as predicted by the master curve for crack initiation toughness. The ʹbuilt inʹ offset between the mean 100 MPa m crack arrest temperature, TK, and RT DT is 38°C (TK = RT 4- 38°C) and the experimental relation between TK and NDT is, TK = NDT + 28°C. The K-reference curve using NDT as reference temperature will be conservative with respect to the general 5Vo lower bound K-curve. with a 75% confidence. The use of RT. instead of NDT, will generally increase the degree of conservatism, both for non-irradiated as well as irradiated materials, close to a 95% confidence level. This trend is pronounced for materials with Charpy-V upper shelf energies below 100 J. It is shown that the K-curve effectively constitutes a deterministic lower bound curve for crack arrest The findings are valid both for nuclear pressure vessel plates, forgings and welds.