Abstract

With ever-increasing computing speed and the enhanced capabilities of commercial finite element analysis software, the use of Elastic-Plastic methods within the ASME Boiler and Pressure Vessel Code has become more widely used for design analysis and fitness-for-service evaluations. The rules in Section III, Appendix XIII, and NB-3200 for pre-2018 versions of the Code, pertaining to the use of “Plastic Analysis” to satisfy the allowable limits for fatigue have been under development in the Section III Working Group on Fatigue Strength. Drawing from methods that are established within ASME Section III Division 5 and Section VIII Division 2, proposed revisions to various sections of Appendix XIII to integrate the use of Plastic Analysis methods into the rules in Section XIII-3440 and -3520 of Appendix XIII are outlined and explained. Additionally, definitions for the calculation of a corollary to the alternating stress amplitude (Salt), referred to as the alternating strain amplitude (εalt), for use in conjunction with the design fatigue curves to calculate a fatigue cumulative usage factor (CUF) are developed. As part of this effort there was an international round robin to evaluate various strain measures and analysis methods, the details of which are documented in a companion paper within this conference. The purpose of this paper is to summarize the proposed changes stemming from the code work and the round robin, and to present the technical justification for use in the balloting process.

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