Study of residual stress fields in thin-walled tubes of stainless steel after drawing

The article discusses investigations of the fields of residual stresses in thin-walled tubes made of stainless steel after drawing. The results of simulation of the finish short mandrel drawing and hand drawing on the coni¬cal mandrel of cold-rolled EI847 steel pipes for fuel cladding of nuclear reactors are presented. A comparative analysis of the dimensional accuracy of pipe obtained in the production and during simulation was made. Differences in sizes of diameters and wall thicknesses are obtained within the TU 14-159-293-2005 standard and show the correctness of the mathematical model. Distributions of residual stresses on pipe walls in case of drawing on short mandrel and in case of hand drawing were obtained. The importance of using hand drawing on the final stage of production of pipes from corrosion-resistant stainless steel is shown. One of the technological features of hand drawing is considered: in the process of pulling the mandrel through the tube the stresses in the deformation area together with the dragging increase providing small plastic stretching of the tube after leaving the mandrel. This fact guarantees the straightness of the pipe manufactured by this method. It is shown that hand drawing on the conical mandrel in the last passage provides favorable distribution of residual stresses on the pipe wall and can be recommended for the improvement of the corrosion resistance of pipes used in the nuclear industry. The technology prospects are shown which can avoid the final cold straightening of tubes leading to the low surface quality as well as to the distortion of fields of residual stresses in the pipe wall.