Section III, non-mandatory Appendix F and mandatory Appendix XXVII provide the evaluation rules for Service Level D loads. Appendix F, article F-1341.2 permits plastic analysis, but provides only a stress-based acceptance criteria. Strain-based acceptance criteria for use in Appendix XXVII is under development. Strain-based acceptance criteria for Level D service limits for piping would be beneficial, especially, for regions where extremely high seismic events exist. A Code Case for strain-based acceptance criteria for level D service limits of piping is being developed in Section III of the ASME Boiler and Pressure Vessel Code. This paper presents the technical basis of the strain-based acceptance criteria Code Case. The authors reviewed extensive literatures which were published over last 50 years to build the foundation of the Code Case. A historical background of the seismic rules is given to explain why the load cycles are limited to 20 as in Section III, Division I, Subsection NB/NC/ND-3622.2 This paper also explains the consideration of reversing dynamic load and non-reversing dynamic load and how they are combined in the analysis. Comparison to current Appendix F (Appendix XXVII) acceptance criteria and some existing test results are provided to show the acceptability and conservatism of this Code Case.

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