AN APPROACH BASED ON CODE CASE 2605 FOR FATIGUE EVALUATION OF VANADIUM MODIFIED MATERIALS REACTOR

摘要

The recent increase in demand of petroleum product has been fulfilled by increase in capacity of refineries. The increases in capacity of refineries have been established by using the heavy wall thickness reactor of material such as 2.25Cr-1Mo-0.25V. The ASME Section VIII Division 2 curves do not extend to creep regime and also and also there is no method in Division 2 to analyze for fatigue or screening using the fatigue curves which is required for material with UTS greater than 80 ksi. Hence, ASME gives the guide lines for the fatigue evaluation & analysis in presence of creep by the Code Case 2605. Code Case 2605 gives the design requirements for fatigue in presence of creep for this material by involving creep ratcheting and creep relaxation procedures. The creep model given in Code Case 2605 is not available in any commercial software like ANSYS, ABAQUS & others. Hence, usercreep model is developed & compiled in FORTRAN software. This usercreep model has been used in ANSYS by TBOPT command from outside ANSYS through FORTRAN. The most critical skirt to bottom head & shell junction in reactor has been analyzed for fulfilling the requirement of Code Case 2605. The elastic perfectly plastic material curve is also used to calculate the plastic strain along with creep strain as required by Code Case 2605. The 0.00071 of accumulated creep damage has been induced at 1,000,000 Hr. Hence, the time of 1,000,000 Hr governs the creep relaxation analysis of Code Case 2605 for fatigue evaluation in spite of limit given on accumulated creep damage in this specific case.