Suggested toughness/temperature relations for reactor pressure vessel steels

Relations are suggested for the means and standard deviations of three toughness measures for reactor pressure vessel steels: static initiation, dynamic initiation, and arrest. All of the relations are of the form: KIx = KLS{1 + exp[(T − [RTNDT + δT])/TO]}, where KIx is the toughness measure of interest, KLS is the lower-shelf toughness, T is the temperature, RTNDT is the reference transition temperature, δT is a temperature shift, and TO is a temperature which characterizes the breadth of the transition. The mean of KLS differs for initiation and arrest and its standard deviation accounts for variation within a single heat. The mean of δT differs for all three toughness measures and its standard deviation accounts for heat-to-heat variability. However, it is shown that a value of To = 33.2°C can be used for all of the toughness measures. Finally, the lower bound curves of the ASME Boiler and Pressure Vessel Code are shown to represent toughness levels of low probability.