1) Work before molding
The raw materials are strip coil, welding wire, and flux. They must undergo strict physical and chemical inspections before being put into use. 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.
2) Molding process
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 steel. Follow the route of the craft and pass the designed meshing point. Using external or internal control roll forming, check whether the perimeter, ovality, straightness, etc. of the steel pipe meet the standard requirements. If it does not meet the requirements, continue to adjust until the requirements are met.
3) Welding process
The welding seam gap control device is used to ensure that the welding seam gap meets the welding requirements. The pipe diameter, the amount of misalignment, and the welding seam gap are strictly controlled. Fine-tune the angle of the rear axle to ensure the formation; when the situation is abnormal, check whether the working width of the steel strip, the pre-bending condition of the edge, the position of the delivery line, the angle of the small roller, etc. have changed, and take corrective measures in time. At present, the Lincoln welding machine is used for single wire or double wire submerged arc welding for internal welding and external welding, to obtain stable welding. The
straight seam steel pipe manufacturer should continuously observe the condition of the forming seam, and should adjust the angle of the rear bridge in time to ensure the forming if there are any misalignments, openings, etc.; and whether there is any change in the angle of the small roller, and take corrective measures in time.
4) Detection
The welded seams are inspected by an online continuous wave automatic flaw detector, 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. When the nominal diameter D ≥ 426mm, the internal defects of the steel pipe should be repaired and welded inside; when D ≤ 426mm, the internal defects are allowed to be repaired from the outside. The weld seam after repair welding shall be ground, and the remaining wall thickness after grinding shall be within the specified wall thickness tolerance. Before the repaired welded steel pipe enters the next process, the steel pipe should be carefully checked to see if any defects are missed or missed, and the next process can be transferred only after confirming that it is correct. The pipe where the strip butt welding seam and the T-joint intersecting with the spiral welding seam are located shall all be inspected by X-ray television or filming. Each steel pipe is hydrostatically tested, and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. The test parameters are automatically printed and recorded.
