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

The conservatism of the RTNDT temperature indexing parameter and the ASME K -IR-reference curve with respect to crack arrest toughness, has been evalua ted. Based on an analysis of the original ASME K-1a data, it was establishe d that inherently, the ASME K-1R-reference curve corresponds to an overall 5% lower bound curve with respect to crack arrest. It was shown that the sc atter of crack arrest toughness is essentially material independent and has a standard deviation (S.D.) of 18% and the temperature dependence of K-1a has the same form as predicted by the master curve for crack initiation tou ghness. The 'built in' offset between the mean 100 h MPa rootm crack arrest temperature, TK1a, and RTNDT is 38 degreesC (TK1a RTNDT 38 degreesC) and t he experimental relation between TK1a and NDT is, TK1a = NDT + 28 degreesC. The K-1R-reference curve using NDT as reference temperature will be conser vative with respect to the general 5% lower bound K-1a(5%)-curve, with a 75 % confidence. The use of RTNDT, instead of NDT, will generally increase the degree of conservatism, both for non-irradiated as well as irradiated mate rials, close to a 95% confidence level. This trend is pronounced fur materi als with Charpy-V upper shelf energies below 100 J. It is shown that the K- 1R-curve effectively constitutes a deterministic lower bound curve for crac k arrest The findings are valid both for nuclear pressure vessel plates, fo rgings and welds. (C) 2001 Elsevier Science B.V. All rights reserved.