Using X-Ray Diffraction and Finite Element Method to Analyze Residual Stress of Tube-to-Tubesheet Welded Joints in a Shell and Tube Heat Exchanger

A lot of failures have been generated in the tube-to-tubesheet joints of a shell and tube heat exchanger, which are greatly affected by the weld residual stresses. In order to ensure the structure integrity, it is very important to predict and decrease the residual stress in the joint between tube and tubesheet. In this paper, a combination of X-ray diffraction and finite element method (FEM) was used to analysis the residual stress distribution in the tube-to-tubesheet joints. The formation mechanism of residual stress before and after cosmetic welding was explicated. The effects of heat input and welding sequence on residual stresses were studied. The results show that the large tensile residual stresses which are in excess of yield strength, are generated in the tube-to-tubesheet joints. The residual stresses at the bottom surface and the edge of the tubesheet are relatively small even become compressive. The formation of the weld residual stress is mainly induced by the cosmetic welding rather than the back welding. The residual stresses increase as the heat input increases. The duplex welding method is recommended to decrease the residual stress.