Numerical investigation of thermo-mechanical stress in U-tube including forming effect for the SCC failure analysis

The U-tube heat exchanger is widely used in process industries. The cracking seems to occur predominantly on the elbow of the U-tube. It is recognized that the tensile residual stress in the tube is a major contributor to Stress Corrosion Cracking (SCC). The Finite Element Method (FEM) is herein used to predict the thermo-mechanical stresses including forming residual stresses. The results of numerical calculation indicate that residual stresses are generated in the elbow of the tube and the forming residual stresses play a critical role in total stresses. Different process parameters including forming temperature, roll gap and the spring back of the tube are discussed, and the results show that higher forming temperature should be selected to reduce the stresses.