Fatigue Analysis for the Lower Assembly of a U-Tube Steam Generator

The lower assembly of a U-tube steam generator consists of a hemispherical primary channel head with a flat bottom, a perforated tubesheet, a partition plate, and a portion of lower shell. The partition plate divides the primary channel head into two halves. Each half contains a primary nozzle and a manway opening. The fatigue analysis of the lower assembly of a U-tube steam generator can be a challenge due to the complexities of the geometry and loading conditions. In this paper, the development of a global finite element model including all important features and several submodels to cover the effects of all these features is described. The tubesheet is simulated using equivalent solid properties with orthotropic material properties. The thermal loads from the inner surfaces of the tubes embedded in the tubesheet are implemented using surface elements. The submodeling technique is utilized to evaluate the local small features, such as tube holes at primary and secondary faces of the tubesheet, with the constraints at the cut-boundaries and the temperature fields of the submodel being extracted from the global model.