In production practice, the steel pipe is often degraded by the wrong side and out of tolerance. Therefore, it is necessary to analyze the reasons for the misalignment of the
spiral steel pipe and its preventive measures. The camber bend of the steel strip is the most important factor causing the misalignment of the steel pipe. In the forming of the spiral welded pipe, the camber bend of the steel strip will continuously change the forming angle, resulting in the change of the weld gap, resulting in seam opening, misalignment, or even overlapping. When the head and tail butt welding seam of the steel strip is large, if it is not handled properly during performing, it is easy to cause a large misalignment. The poor edge condition of the strip is another important cause of misalignment.
(1) The raw materials are strip coil, welding wire, and flux. They must undergo strict physical and chemical inspections before being put into use.
(2) The head and tail of the strip are butted by single-wire or double-wire submerged arc welding, and automatic submerged arc welding is used for repair welding after rolling into a steel pipe.
(3) Before forming, the strip is leveled, trimmed, planed, surface cleaned and conveyed, and pre-bending.
(4) The weld gap control device is used to ensure that the weld gap meets the welding requirements, and the pipe diameter, misalignment, and weld gap are strictly controlled.
(5) Adopt external control or internal control roll forming.
(6) The electric contact pressure gauge is used to control the pressure of the cylinders on both sides of the conveyor to ensure the smooth conveying of the strip.
(7) After cutting into a single steel pipe, each batch of three steel pipe heads must undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion status of the weld, the surface quality of the steel pipe, and non-destructive testing to ensure the pipe making process. Only after passing the test can it be officially put into production.
(8) Use an air plasma cutting machine to cut the steel pipe into single pieces.
(9) Both internal welding and external welding are used for single-wire or double-wire submerged arc welding by the American Lincoln welding machine, to obtain stable welding specifications.
(10) The welded seams are all inspected by the online continuous ultrasonic automatic flaw tester, which ensures 100% non-destructive testing coverage of the spiral welds. If there is a defect, it will automatically alarm and spray the mark, and the production workers can adjust the process parameters at any time accordingly to eliminate the defect in time.
(11) The parts with continuous sonic flaw detection marks on the welds shall be re-examined by manual ultrasonic wave and X-ray. If they are indeed defective, after repairing, they shall undergo non-destructive inspection again until it is confirmed that the defects have been eliminated.
