Residual stresses in roller expanded tube-tubesheet joints with large initial clearance and grooves

Heat exchanger tube rolling introduces tensile residual stresses in the expanded part of the tube and the transition zone between the expanded and unexpanded regions of the tube. These tensile residual stresses accelerate fatigue crack initiation and enhance small crack propagation and may cause stress corrosion cracking of the tube if it is exposed to a corrosive environment. In this paper, an axisymmetric finite element model has been used to evaluate the effect of large initial tube-tubesheet radial clearance and to evaluate the effects of grooves machined in the tubesheet hole on the distributions and magnitudes of the radial deformation of tube walls and the residual stresses along the expanded length of the tube and in the transition zone. The results have revealed the presence of tensile and compressive residual axial and hoop stresses in the inner and outer surfaces of the tubes with various degrees of severity.