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

Abstract

The current Section VIII Division 2 of ASME code permits only the method based on experience with comparable equipment of paragraph 5.5.2.2 to be used for the exemption from fatigue analysis when the design allowable stress is taken in the time dependent temperature range and the specified minimum tensile strength is greater than 552 MPa. In the case of 2.25Cr1Mo0.25V steels, the allowable stress of new Div.2 is higher than that of the old Div.2. Therefore, there are no experiences with comparable equipment. Code Case 26051 provides rules for fatigue evaluation of 2.25Cr1Mo0.25V steels at temperatures greater than 371 آ°C and equal to or less than 454 آ°C. An inelastic analysis including the effect of creep is required to be performed for all pressure parts according to Code Case 26051. There are six and more types of nozzles in each hydroprocessing reactor. The inelastic analyses shall be performed for all types of nozzles. The simplified screening method for fatigue analyses and the simplified fatigue analysis procedure need to be developed because it takes much time to perform inelastic analyses. This paper provides sample analysis results for various types of nozzles and clarifies issue with respect to implementation of Code Case 26051. Then, a proposal for simplification and modification of Option 1 and Option 2 fatigue evaluation methods for nozzles of Code Case 26051 are proposed from these investigations.