National University of Science and Technology “MISiS” (Moscow, Russia):

V. N. Shinkin, Dr. Phys.-Math., Prof., e-mail: shinkin-korolev@yandex.ru

In the production of the large-diameter steel pipes for the main gas-oil pipelines according to UOE technology at TESA 1020, the steel sheet is bent on the edge bending press, the pre-forming press and the final forming press. On the edge bending press, the longitudinal edge of the steel sheet is bent according to the one-radius or tworadius scheme along the entire length of the sheet, fi rst on one side, and then on the opposite side. On the pre-forming press, the steel sheet is given a U-shape by bending its central part. The final forming press gives the steel sheet an O-shape, which is close to the pipe’s shape and convenient for welding the billet’s edges. Next are the assembly and welding of O-billet of pipe at an electrical welding machine, the finishing of pipe’s roundness at an expander, the hydraulic testing of pipe for strength and the pipe’s coatings with an external and internal anticorrosion protection. When the steel sheet is deformed on the O-press, the excessively curved sections of the sheet are partially unbent in the opposite direction, and the insufficiently curved sections receive additional bending in the original direction. The calculation of sheet’s curvature at the alternating bending causes the signifi cant difficulties for metallurgical technologists because of Bauschinger’s effect at bending, in which the mechanical characteristics of the steel significantly change. In consequence, the defects in the O-shape of the pipe billet often occur after the final forming press — the insufficient roundness of the billet (at which the gap between the edges of the billet is unacceptably large), the edges’ displacement of the billet (at which the edges of the billet are at different levels one above the other) and the
overlapping longitudinal edges of the billet (when the billet’s edges are X-shape shifted relative to each other in the contact area or are not in contact with each other and are located one above the other). The defect of the edges’ overlap of the pipe billet is difficult to remove, since in this case the billet before the welding has to be a partially unbent with the jacks. In this paper, we propose the analytical method for calculating the final curvature of steel pipe billet at the alternating bend at TESA 1020. The results of the paper can be applied in metallurgy at the production of thick-walled large-diameter steel pipes.

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