Evaluation of the ASTM and ISO J initiation procedures by applying the unloading compliance technique to reactor pressure vessel steels

Other than the brittle failure, the ductile behavior of the aged reactor pressure vessels (RPV) steels is also of interest for the integrity assessment and the evaluation of the irradiation response. The fracture toughness of high toughness materials like RPV steels can be characterized by a J-R curve. Since, the RPV steel material available for testing purposes, like surveillance specimens is limited the single specimen method is used for J-R curve determination. In this study, J-R curves were measured on Charpy size SE(B) and 1T-C(T) specimens of different RPV steels in the un¬irradiated and irradiated condition. It was observed that despite the available sophisticated instrumentation and strict implementation of the recommended test procedures, J-initiation value for all the different material specimens tested, could not be ascertained according to the tests standards ASTM E1820-09 und ISO 12135. For charpy size SE(B) specimens, it was found that though in irradiated condition valid JIc/J0.2BL values could be obtained but in un-irradiated condition especially for high toughness RPV steels it was not possible. The evaluation showed that the aoq fit of the ASTM standard compensates uncertainties in the initial J-Δa value resulting in reliable and more number of qualified test results. But these uncertainties strongly influence the A parameters of the ISO fit and the J0.2BL(B) value. Additionally, in ISO evaluation, the lower offset of the first exclusion line and a higher slope results in lower J0.2BL values compared to ASTM analysis. Furthermore, for the two specimen geometries the course of J-R curves up to the JQ value was similar even for high toughness material, but the lower specimen size was disqualified due to the lower prescribed Jlimit.. Similarly, the J-R curves for un-irradiated and irradiated condition had a similar course up to the J0.2BL value, even for extremely high irradiation induced embrittlement.