Development of Generic Unirradiated Values of T0 and RTTo for Use in ASME Code Applications

Abstract A companion paper presented at this conference summarizes a recently published EPRI report that provides a Technical Basis for Code Case N-914, “Accounting for the Effect of Embrittlement on Fracture Toughness Properties Used in Evaluations of Pressure Boundary Materials in Class 1 Ferritic Steel Components, Section XI, Division 1.” CC N-914 is being developed by the Section XI Working Group on Operating Plant Criteria to provide a consistent and comprehensive methodology to account for embrittlement, including the effects of uncertainty, for both conventional Code applications that use RTNDT as an index temperature as well as newer methodologies that adopt the Master Curve based reference temperatures T0 or RTTo. At least in the United States it has become common practice to sometimes use “generic” values of unirradiated RTNDT that have been established as mean values for a class of materials (e.g., a weld made from a particular weld wire heat, a plate made to a certain ASTM specification, etc.) along with an associated uncertainty term in situations where a plant/material specific RTNDT value is not available. The objective of this paper is to describe a methodology that can be used to establish similar generic unirradiated values for RTTo and T0 using data published in the open literature. Such values provide a low-cost point of entry for use of Master Curve techniques such as those now in the Code itself and in various Code Cases (e.g., CC N-830-1, proposed CC N-914). Generic values may provide relief from excessively conservative RTNDT estimates while plant-specific Master Curve data is being developed.