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ASME Code Cases N-629/N-631, published in 1999, provided an important new approach to allow material specific, measured fracture toughness curves for ferritic steels in the code applications. This has enabled some of the nuclear power plants whose reactor pressure vessel materials reached a certain threshold level based on overly conservative rules to use an alternative RTNDT to justify continued operation of their plants. These code cases have been approved by the US Nuclear Regulatory Commission and these have been proposed to be codified in Appendix A and Appendix G of the ASME Boiler and Pressure Vessel Code. This paper summarizes the basis of this approach for the record.

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It has long been recognized that there is a considerable difference between the dynamic and quasi-static fracture toughness reference temperature. However, it has not been clear whether this loading rate effect extends into the quasistatic loading regime. The current fracture toughness reference temperature test standard for ferritic steels (ASTM E1921) specifies an allowable quasi-static loading rate range spanning 100 fold. Recently obtained data from the IAEA JRQ material suggests that the same loading rate effect extends throughout this allowable quasi-static loading rate range. The loading rate effect could amount to a difference in the measured reference temperature of 23°C (41°F) between the extremes of the specified range. This paper presents the data demonstrating this effect, examines different ways of calculating the loading rate, suggests changes to related to the test standard, and discusses the use of applying the loading rate effect on reference temperature.