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

M. A. Tovmasyan, Post-Graduate, e-mail: i-margarit@yandex.ru
S. V. Samusev, Dr. Eng., Prof.

The results of studies to assess the effect of stresses and strains that occur during welding on a pipe shape in the transverse direction have been presented. To determine the pipe ovality, measurements of the gap width, horizontal and vertical diameter after each deformation process at the incremental forming - expansion stage were made. The results of ovality measurements for the front and rear ends of pipes (1219 × 17.5 of K65 strength class; 1220 × 20 mm, 1220 × 17.3 mm of K60 strength class; 1220 × 12 mm, 1020 × 10 mm of K52 strength class) after the incremental forming, assembling and welding of the technological seam, internal and external seams and expansion, as well as changes in ovality after each process under consideration were presented. Pipes of K52 strength class with a diameter to wall thickness ratio of 101.6 had the largest deviation in ovality, the smallest (55) had pipes of K60 strength class, pipes of K65 strength class had a value of 69.7. When welding the inner and outer seams, the vertical diameter increases, and the horizontal diameter decreases. The total change in the ovality of pipes because of residual welding strains is 0.7–3 %. After welding the outer seam, 7 % of the pipes had a horizontal oval at the rear end and 1 % at the front end. After expansion, most of the pipes had a horizontal oval, and the ovality value of the pipes at the rear end exceeded the ovality value of the pipes at the front end. In order to assess the change in the pipe shape in the heat-affected zone, we measured pipe diameters of 1220 × 17.3 mm of the K60 strength class at a distance of 100 mm from the weld and the deviation from the theoretical circumference in the marginal zone before and after expansion. The greatest deviation from the theoretical circle to the oval for the front and rear ends had pipes with the “apple” shape in the marginal zone.

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