Finite Element Analysis of Skirt to Shell Junction in a Pressure Vessel

Objectives: The objective of this research work is to find the effect of providing hotbox at skirt to shell junction of a pressure vessel on the stresses induced at this junction. Methods/Statistical Analysis: In present work, since the vessel is to be supported at some elevation from ground, a conical skirt support is used. Two models of skirt to shell junction are made, in Unigraphics 10, one without hotbox while other with hotbox. A thermo-structural analysis of models is performed using ANSYS Workbench15. Stress linearization is done and stresses are limited to code allowable to ensure protection against plastic collapse and local failure. Findings: The result of finite element analysis for the case of model without hotbox shows that thermal stresses as high as 329 MPa are induced at the y-ring, which is much higher than the allowable stress at that temperature. When a hotbox is provided at this region, the stress is found to be reduced to 35.082 MPa, which is less than the allowable stress. So, the vessel will work safely if a hotbox of minimum 480 mm length is provided at the critical junction of skirt and shell. Stress is linearized at five stress classification lines. The linearized stresses and their combinations for four load cases are compared with the code allowable limit, and are found to be less than allowable stress. This ensures the protection of vessel against plastic collapse and local failure. Application/Improvements: Such analysis is needed to be performed for long vessels supported on skirt type of support, as the total vessel loads will be transferred to skirt from this junction only.