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The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code reference toughness curves are based upon an approach which utilizes a material normalizing and indexing parameter, RTNDT. This parameter is based upon the combined results from Charpy V-notch and drop-weight nil-ductility transition temperature tests as defined in the ASME Code. In many cases, this indexing parameter is overly conservative relative to the real toughness of ferritic reactor pressure vessel (RPV) steels, and a more direct index and measure of the true fracture toughness is desired. The Master Curve fracture toughness method, recently issued as ASTM Standard Test Method E 1921-97, is a better indicator of fracture toughness behavior in terms of a directly measured toughness index, To, and statistically-derived tolerance bounds. This method is technically more sound than the RTNDT approach and provides use of the statistical nature of measured fracture toughness properties (including use of surveillance materials). The Pressure Vessel Research Council (PVRC) is presently investigating application of the Master Curve approach for implementation in the ASME Code. The Electric Power Research Institute (EPRI) is supporting development of alternative RPV integrity assessment approaches, which includes documentation of the technical basis for application of the Master Curve approach. An EPRI document has been written that supports the ASME Code activities to allow utility use of the Master Curve approach. The results of that document for application of the Master Curve approach to RPV integrity assessment are summarized in this paper. Examples illustrating applicability of the Master Curve approach are presented.
fracture toughness, master curve, reactor pressure vessel steels, ASME Code, reference temperature, nuclear pressure vessel
President, ATI Consulting, Pinehurst, NC
Program Manager, EPRI, Charlotte, NC