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.
Bendability and failure mechanisms of dual phase steel under air-bending at elevated temperatures
