Abstract

In the ductile–brittle transition temperature range, the Charpy absorbed energy exhibits an inherent variation, which causes uncertainty in the transition temperature shift. In the current codes for the evaluation of fracture toughness of reactor pressure vessel steels, margins are considered to account for the uncertainty in the transition temperature shift. Although they have been statistically determined, their adequacy is only inductively assured by specific surveillance program databases. In this study, a model was proposed to describe the statistical characteristics of the transition temperature shift. An equation to describe the standard deviation of the associated transition temperature was theoretically derived from a previously proposed variation model of the Charpy absorbed energy according to the law of propagation of uncertainty. The obtained standard deviations were then compiled into procedures to estimate the transition temperature shift according to the sufficiency of the parameters required for the evaluation (shape of Charpy curve and sample size). The standard deviations of the transition temperature shift assumed in past studies/present codes were compared with those predicted using the proposed model. In the range of upper shelf energy greater than 100 J, the standard deviations in past studies/present codes encompass the estimates obtained using the proposed model. Therefore, the inherent variation in toughness appears to be considered conservatively.

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