Practical Application of the New Homogeneity Screening Procedure Added to ASTM E1921-20 and Appendix X5 Inhomogeneous Data Treatment

In 2019, the ASTM E08.07.06 subcommittee added a homogeneity screening procedure to ASTM E1921, Standard Test Method for Determination of Reference Temperature, To, for Ferritic Steels in the Transition Range. The screening procedure is intended to determine if the data set may be representative of a macroscopically inhomogeneous material. If the material fails the screening criterion, the subcommittee added Appendix X5, "Treatment of Potentially Inhomogeneous Data Sets," to enable more accurate assessment of the material. Several existing large fracture toughness data sets of reactor pressure vessel low alloy steel plates, forgings, and welds were assembled to evaluate the homogeneity screening procedure and the Appendix X5 treatment methods. Several subsets of data from each of the large data sets were separately evaluated. The small data subsets are intended to approximate the number of specimens generally tested for an irradiated material (typically less than 20). The data set is screened and, if found inhomogeneous, treated according to the procedure in Appendix X5 that applies to small subsets of data. The results from the various subsets are compared with the parent large data set to assess the ability of the least conservative data subsets to bound the full data set. It is shown that, depending on the screening outcome, different margin adjustments than those recommended in ASTM E1921-20 can be used to provide results that bound a high percentage of the data. In addition, the experience presented in interpreting and using the procedures for the various data subsets has provided valuable insight for future applications.