Application of the Master Curve in the ASME Code

Abstract

The ASME Code reference toughness curves are based upon an approach that utilizes a material normalizing and indexing parameter, RT NDT. This parameter is based upon the results from Charpy V-notch and drop weight nil-ductility transition temperature tests as defined in the Code. In many cases, this indexing parameter is overly conservative relative to the real toughness of ferritic pressure vessel steels, and a more direct index and measure of the true fracture toughness is needed. The American Society for Testing and Materials (ASTM) recently documented Standard E1921-97 for the determination of a directly measured toughness temperature index, T 0, through use of the Master Curve approach. Efforts are underway in the ASME Code to utilize the Master Curve approach, and the determination of T 0, to provide an alternative definition to the existing reference temperature, RT NDT, and statistically defined fracture toughness curve(s) for unirradiated and irradiated ferritic pressure vessel steels. In the technical basis document, published by EPRI, the Master Curve fracture toughness method is profiled as a better indicator of fracture toughness behavior in terms of a directly measured toughness temperature index. The document also provides technical arguments in support of using the Master Curve fracture toughness approach for defining a new fracture toughness-based reference temperature, RT T0 . This paper discusses the ASME Code efforts to utilize the Master Curve approach and outlines the technical basis for determination of an alternative reference temperature, RT T0 , for use in reactor pressure vessel integrity assessment.