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

V. N. Shinkin, Dr. Sci. (Phys.-Math.), Prof., shinkin-korolev@yandex.ru

The length of modern main gas-oil pipelines often reaches several thousand kilometers, and the pipelines are composed from an enormous number of steel large-diameter pipes. The production of the single-joint longitudinally welded steel pipes for main gas pipelines with a length of from 12 to 18 m, a diameter from 1020 to 1420 mm, a wall thickness from 19 to 48 mm from the steels of the strength classes from К38 to K65 is carried out in Russia at JSC “Vyksa Steel Works”, JSC “Izhora Pipe Mill” and JSC “Chelyabinsk Pipe-Rolling Plant”, as well as abroad at the pipe plants of the United States, Germany, China and India. During the ground laying of main pipelines in the trenches on the areas with a rugged terrain (“Yamal-Center”, “Sakhalin-1”, “Sakhalin-2”, “Eastern Siberia - Pacific Ocean”) or the submarine pipeline laying on the seabed (“Nord Stream”, “Turkish Stream”) the main large-diameter pipes experience the significant elastic and plastic bending deformations, which can lead to the industrial defects of main pipelines and the walls of main pipes. After the land and underwater laying, the main pipelines’ pipes springback and fully or partially become straight, however, under an elastoplastic bending their residual longitudinal curvature is significantly different from zero. Under an excessive residual curvature, the main pipelines may have defects that are not compatible with the operational rules for pumping of gas and oil under a high-line pressure (from 1.2 to 10 MPa), or even to collapse. Disaster on the main pipelines often have the difficult removable environmental consequences on a global scale. Therefore, it is important to know the springback coefficient of the pipe during bending, allowing to calculate the residual curvature of the pipe after bending. In this paper we have obtained the springback coefficient of the pipe under bending for an elastoplastic medium with a linear hardening, depending on the diameter and the wall thickness of the pipe, the yield strength, the young's modulus and the hardening modulus of pipe’s material. The research results can be used in the metallurgical and machine-building factories as well as in the construction of the gas-oil main pipelines.

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