Determination of the Transition Temperature Scatter Using the Charpy Data Scatter

For a pressure vessels integrity assessment it is necessary to know the transition temperature of metal. It is defined from the hyperbolic tangent curve, which best approximates the Charpy V-notched (CVN) impact tests data, as the temperature corresponding to some fixed Charpy impact energy. However, when planning experiments, processing of the results, and interpreting of the resulting transition temperature, two problems arise which have not been studied in the literature. First — sufficiency of the CVN impact tests data for a curve fit building and transition temperature determination. Second — experimental data scatter accounting while determining the transition temperature. This work proposes to define two quantitative characteristics: the “importance” of each CVN impact test for the defined transition temperature; the transition temperature scatter which is calculated from the Charpy impact energy data scatter with consideration of the above “importance”. Also the data points sufficiency criterion for adequate defining the transition temperature is formulated. Numerical experiments carried out on sets of test data have shown a good correlation between transition temperatures scatter calculated by the standard method and by the one developed in the present paper. Analysis of RPV weld metal surveillance data in the initial and irradiated conditions for Unit 1 and 2 of South-Ukrainian NPP shows that the transition temperature scatter, determined in this way, reaches 26°C.