In 1999, we assessed the applicability of the Master Curve procedure (ASTM E1921-97) to the measurement of the reference temperature for a reactor pressure vessel steel (20MnMoNi55) characterised by different type of cleavage initiators.
In this study, we applied and extended the same approach to three well-characterised reactor pressure vessel steels (22NiMoCr37, JSPS, JRQ). The applicability of the following aspects of the Master Curve methodology were investigated, using statistical tools such as the Generalised Maximum Likelihood (GML) and Monte Carlo methods:
- independence of To from test temperature and specimen type (configuration/dimensions);
- values prescribed for the Weibull exponent (m = 4) and minimum toughness (Kmin = 20 MPa?m);
- 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 and Kmin).
The main achievements of this study, in reference to the three RPVS investigated, were the following:
- To is independent from the temperature, within the range prescribed by the ASTM standard.
- The reference temperature measured on C(T) specimens of different size is effectively independent from the sample dimensions; the well-known 10 - 15 °C difference was found between PCCv and C(T) geometries.
Not enough experimental evidence was available to justify alternative values for the parameters of the Master Curve approach (m and Kmin), although not in all cases the outcome of the Monte Carlo analyses performed included the codified values (m = 4 and Kmin = 20 MPa?m).
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 of m (with respect to the number of valid data r) and Kmin (with respect to the median toughness).
The proposed relationships for estimating KJc,med and sigma-To for the multi-temperature analysis have been validated by comparison with the results of the Monte Carlo method: excellent agreement was found in terms of sigma-To.
|Place of Publication||Mol, Belgium|
|State||Published - 2001|
|Publisher||Studiecentrum voor Kernenergie|