No abstract

Used in order to turn the line of trunk pipelines in horizontal and vertical planes, cold bends are the simplest and most economical elements to be manufactured. Their smaller rotation angle compared with other types of bends is, however, a disadvantage. The article presents the results of cold bends, experimentally manufactured from K56 strength class pipes to have an increased bending angle compared to that stated in regulatory requirements; also, it contains test results regarding metal samples taken from deformed and undeformed sites of the experimental bends. It was found that 720×8 mm and 1020×17 mm bends at rotation angles of up to 13 and 9.1°, respectively, retain satisfactory geometric parameters and are not prone to corrugations. A study on how hardening at cold deformation affects the change in the mechanical properties of deformed bend sites showed that the values of temporary resistance, yield strength, elongation, and impact strength comply with regulatory requirements. It was revealed that the delivery state of the rolled stock of the initial bare pipe affects the level of impact strength and the cold brittleness threshold attributed to the bends: thus, when testing the bent-out metal after high tempering, a higher level of toughness together with a higher cold brittleness threshold were revealed compared to those obtained when testing the bent-out metal after controlled rolling. In general, experimental studies confirmed that cold bends with an increased bending angle could be manufactured from Russian-made pipes of K56 strength class. Such bends used to construct a trunk pipeline will contribute to reducing the total number of bends, the amount of work and, consequently, the cost of construction.

Determination of causes of crack-like defects in the heavy plate steel 09Г2С is a crucial task, the solution of which is aimed at improving the mechanical safety of oil storage steel vertical tanks. In order to determine the causes for the formation of a group of crack-like defects oriented towards rolling, revealed during grinding and magnetic inspection of the tank wall surface near the vertical weld, the analysis of the chemical composition and testing of the mechanical properties of heavy plate steel were carried out, including the determination of the anisotropy of impact toughness in the temperature range from +20 to –75 °С, analysis of metal microstructure in the area of defect formation on transversal sections and rolled surface. Impact bending tests of 09Г2С heavy plate steel after controlled rolling in longitudinal and transverse directions showed no anisotropy of impact toughness, as well as high purity of steel as for sulfur and titanium, which at higher content causes impact toughness anisotropy. The revealed features of metal microstructure near the defects made it possible to conclude that the crack-like defects were formed during the rolling of gas bubbles at the stage of preparing semi-finished rolled products for finishing rolling. One of the possible methods to prevent such defects from getting into finished rolled products is the use of automated systems of visual inspection of rolled products in the manufacturing process.