Residual Stress Modeling of Induction-Bent Pipes

The induction bending process using local induction heating is widely used to produce large diameter pipes with relatively small bend radii at low tooling cost. This process was considered for the fabrication of stainless steel feeder pipes for CANDU® reactors instead of cold and warm bending processes. Wall thickness measurements were performed, before and after bending, using an ultrasonic testing method on a number of test bends fabricated with this induction bending process. Residual stress measurements have been performed on a test bend by X-ray diffraction. A numerical model has been developed using LS-DYNA® to predict the residual stress and the deformed shape of these bends. The numerical model has also been used to study the effect of some key input parameters, such as bending speed, bending temperature, process parameters of induction heating and cooling, and the yield strength of the feeder material. This information can be used to improve the bending process such that lower residual stress and more uniform wall thickness can be achieved. In this paper, the simulation work is summarized and the comparison between the simulation results and the measurement data are presented.