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.
A set of equations are developed for a disk-shaped compact (DC(T)) specimen to be used in conjunction with ASTM E 1152-87 standard which is for determining J-R curves using rectangular compact specimens. A slightly different disk-shaped tension specimen design (BWDC(T)) is used by B&W Owners Group in their Integrated Reactor Vessel Material Surveillance Program [1] (IRVSP). This specimen is analyzed by a finite element method to investigate whether the standard DC(T) compliance relationship is appropriate for use. Validation tests using both square C(T) and DC(T) specimens were performed and the resulting J-R curves are compared. It is concluded that using this procedure both C(T) and BWDC(T) specimens yield similar J-R curves.
A tentative test procedure for the determination of the plane strain-crack growth resistance JI-R curve for metallic materials is presented. This procedure was prepared by a Working Group of ASTM Committee E24.08.03. It was evaluated with a round robin test program on HY130 steel, conducted in 1980 to 1981. The results of the testing program were reported in a companion paper, and the experiences were incorporated in this procedure. The procedure is written for the elastic compliance method of developing the plane strain JI-R curve. Recommended specimens are the pin-loaded compact and the three-point bend specimens. Details regarding apparatus, specimen preparation, test system calibration, testing, calculation of J and crack extension, and data qualification are specified.
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