Assessment of the master curve approach on three reactor pressure vessel steels

Abstract

This study aims at assessing the applicability of the Master Curve procedure to the measurement of the reference temperature for three well-characterised reactor pressure vessel steels (22NiMoCr37, JSPS, JRQ). The following aspects of the methodology were investigated, using statistical tools such as the Generalised Maximum Likelihood (GML) and Monte Carlo methods: independence ofT _o from test temperature and specimen type (configuration/dimensions); formula given in ASTM E1921 for evaluating the standard deviation of the reference temperature, and possibile expressions for estimating the standard deviation of the other Weibull parameters (m andK _min); proposed relationships for estimating the median toughness and standard deviation forT _o (σ _{T o}) in the case of multi-temperature Master Curve analysis. In reference to the three Reactor Pressure Vessel Steels (RPVS) investigated, the independence ofT _o was assessed from the test temperature (within the range prescribed by the following revision of the ASTM standard,T _o ± 50 °C) and, as far as C(T) specimens are concerned, from the sample dimensions; the well-known 10 ÷ 15 °C difference was however found between PCCv and C(T) geometries. Furthermore, using the Monte Carlo method, we assessed the relationship proposed by the ASTM standard for estimating the standard deviation of the reference temperature, which results fairly conservative; an alternative analytical function has been proposed. Clear trends have also been identified for the standard deviation ofm (with respect to the number of valid datar) andK _min (with respect to the median toughness). Finally, the proposed relationships for estimatingK _Jc,med andσ _{T o} for the multi-temperature analysis have been validated by comparison with the results of the Monte Carlo method: an excellent agreement was found in terms ofσ _{T o} (better than 0.2 °C).