Fatigue Verification of Class 1 Nuclear Power Piping According to ASME BPV Code

In this paper, fatigue verification of Class 1 nuclear power piping according to ASME Boiler & Pressure Vessel Code, Section III, NB-3600, is addressed. Basic design requirements and relevant verification procedures using Design-By-Analysis are first reviewed in detail. Thereafter, a so-called simplified elastic-plastic discontinuity analysis for further verification when the basic requirements found unsatisfactory is examined and discussed. In addition, necessary computational procedures for evaluating alternating stress intensities and cumulative damage factors are studied in detail. The authors' emphasis is placed on alternative verification procedures, which do not violate the general design principles upon which the code is built, for further verification if unsatisfactory results found in the simplified elastic-plastic analysis. An alternative which employs a non-linear finite element computation and a refined numerical approach for re-evaluating the cumulative damage factors is suggested. Using this alternative, unavoidable plastic strains can be correctly taken into account in a computationally affordable way, and the reliability of the verification will not be affected by uncertainties introduced in the simplified elastic-plastic analysis through the penalty factor K(subscript e) and other simplifications.