An analytical investigation of the applicability of simplified ratchetting and creep-fatigue rules to a nozzle-to-sphere geometry

This paper presents an analysis of a nozzle-to-spherical-shell attachment and explores the applicability of simplified ratchetting and creep-fatigue rules to this attachment. A five-cycle inelastic analysis and creep-fatigue damage evaluation was carried out. Ten lines, or critical sections, were chosen for postprocessing to determine the ratchetting strain and creep-fatigue damage at both the inside and outside surfaces. At many of the 20 surface points analyzed, the inelastic analysis results did not develop a constant or decreasing pattern for the incremental strain or damage even after 5 cycles were analyzed. Failure to develop a constant or decreasing pattern was especially prevalent for creep damage. The results of the detailed inelastic analyses at the ten critical sections are compared with the results of elastic evaluations of ratchetting and creep-fatigue damage calculated results of elastic evaluations of ratchetting and creep-fatigue damage calculated according to ASME Boiler and Pressure Vessel Code Case N-47-13. The elastic ratchetting procedures were found to be conservative for all ten sections. The elastically calculated creep damage was nonconservative for two sections. A new technique for simulating a two-dimensional inelastic structure by a series of one-dimensional inelastic membrane shell analyses was also developed