Applications of Code Case 2605 for Fatigue Evaluation of Vessels Made in 2.25Cr-1Mo-0.25V Steels Slightly Into Creep Range

The current Section VIII Division 2 of ASME code does not permit method A of paragraph 5.5.2.3 to be used for the exemption from fatigue analysis when the design allowable stress is taken in the time dependent temperature range. Method B of paragraph 5.5.2.4 also cannot be used because it requires the use of the fatigue curve which is limited to 371 ° C and below the needed temperature. Code Case 2605 is a rule for fatigue evaluation of 2.25Cr-1Mo-0.25V steels at temperatures greater than 371 ° C and less than 454 ° C. An inelastic analysis including the effect of creep shall be performed for all pressure parts according to Code Case 2605. Especially, a full inelastic analysis shall be performed using the actual time-dependent thermal and mechanical loading histograms for the lateral nozzle based on preliminary study. It takes much time to perform this inelastic analysis for all full histograms and obtain the fatigue evaluation results when large number of cycles of full pressure is specified in user’s design specification. This paper provides sample analysis results for nozzles and clarifies issue of implementation of Code Case 2605. Then, the proposal of simplification and modification of Code Case 2605 from these results are proposed.