Development of the method for determining the deformation parameters and remidal stresses of metal in the manufacture of straight-seached pipes of large diameter using expansion

Abstract

Since 2020, in Ukraine, LLC NVP «UKRTRUBOIZOL» began to operate a technological line for the production of large-diameter pipes (TVD) for main oil and gas pipelines with a hydromechanical expander. From 2023, interstate GOST 20295-85 and GOST 10706-76 ceased to be valid in Ukraine. Formulation of the problem. Ukrainian standards are needed. It is necessary to determine the rational values of the deformations and the effectiveness of the expansion to reduce the residual stresses in the metal of the pipes. Goal. Development of Ukrainian standards for TVD production and determination of the effect of expansion on residual stresses. Method. The method of cutting rings was used. The results. Developed and implemented with the participation of author: DSTU 9219:2023; DSTU 9218:2023 and TU 24.2–05757883–095:2022. Pipes with a diameter of 630 mm, with a wall of 8 mm, made of S335 steel and hot-rolled rolled sheet were studied. The opening between the longitudinal edges of the pipe blank after bending was 70-80 mm. For the ring after welding, the opening was 180 mm and for the rings expanded by 0.8%, 1.2% and 0.4% -58-53 mm. This indicates that the residual expansion stresses were much smaller than in the pipe after welding the seam, and the amount of expansion change from 0.4% to 1.2% does not affect the residual stresses. Scientific novelty. For the first time, for the JCOE technology of production of TVD from rolled hot-rolled sheet, the influence of expansion on residual stresses was determined experimentally. It was shown that the opening of the rings during expansion is significantly reduced. For the first time, the influence of the amount of expansion on the reduction of residual stresses was determined for the JCOE technology of TVD production. It is shown that deformations of 0.4-1.2% give the same opening of the rings after expansion. Practical significance. The obtained results can be useful for the personnel of steel welded TVD production enterprises and project organizations sn the design of oil and gas pipelines