Recent Advances in ASME Code Section XI Appendix K for Low Upper Shelf Toughness Evaluation

Abstract The ASME Code Section XI Working Group on Flaw Evaluation members developed Appendix K to handle the assessment of low upper shelf materials dating back to extensive work done in the 1980s. Appendix K has remained basically unchanged since that time. A new version has been recently passed by the Code Committee which will be included in the 2025 Edition of the Code. This paper describes the changes that have been made to upgrade the materials characterization aspects as well as allowance for modern methods for transient definition and integrity assessment. The materials characterization definitions for the crucial J-integral resistance (J-R) curve have been broken into four areas: (1) an old correlation based on a database of J-R curves and material type, (2) addition of a new predictive methodology requiring measured Master Curve reference temperature T0 and its statistical correlation with a large database of J-R curve results based on the methodology in ASME Code Case N-830-1, (3) direct measurement of material J-R curves with requirements relative to the number of tests and applicability to neutron fluence conditions and test specimen orientation, test temperature, and material condition, and (4) other methodologies that can be reviewed by the regulator. One aspect that may still be added relative to the direct J-R curve measurement option is a test temperature minimum requirement for use when small fracture toughness specimens are tested with sizes less than a one-inch (25.4 mm) thick compact tension specimen [1T-C(T)]. Guidance or a cautionary note relative to the minimum test temperature for the testing of these smaller specimens is currently being discussed by the Code Committee.