FINITE ELEMENT MODELING OF THICK WALLED VESSELS UNDERGOING LOCALIZED POST WELD HEAT TREATMENT

Usage of thick walled vessels is important for equipments operating under high temperature and pressure. Post weld heat treatment (PWHT) has been used for stress relief purpose and to improve mechanical properties at welded joints of these equipments during fabrication or repair. Cracks and fatigue failures are the main problems when localized PWHT were performed at weld joints near thick structures because sufficient since ideal heat transfer and proper temperature gradients cannot be achieved. This project studied the effect of these geometrical constraints on thermal distribution and stress level when localized PWHT is applied. Finite element analysis (FEM) using ANSYS™ were performed on 2D models of pressure vessel having different adjacent structures and under several PWHT conditions. Simulation results show significant increase in radial thermal gradients up to 60oC with the presence of thick adjacent structures near the weldment. Thermal stress also increases with the addition of those structures, mainly on the tubesheet side. Increase in heating band width gives better thermal distribution for local PWHT compare to decreasing the rate of heating and cooling.