1. Prospecting: Once the steel plate intended for manufacturing large-diameter SAW (Submerged Arc Welded) straight-seam steel pipes enters the production line, a full-plate ultrasonic inspection is conducted first to ensure material quality and detect any internal defects.
2. Milling: The edges of the steel plate are double-sided milled using a milling machine to achieve the desired width, edge parallelism, and groove shape, preparing it for the forming process.
3. Pre-crimping: A pre-bending machine is used to shape the edges of the steel plate, giving them the necessary curvature for the next stage of the manufacturing process.
4. Forming: In the JCO forming machine, the pre-bent steel plate is punched and pressed into a "J" shape on one side, then the other half is bent and pressed into a "C" shape, forming an open "O" shape. This step is crucial in shaping the pipe into its final form.
5. Pre-welding: The formed straight-seam steel pipe is seam-welded using gas-shielded metal arc welding (MAG), ensuring a strong and consistent weld before the final welding stages.
6. Internal Welding: An automatic vertical multi-wire submerged arc welding system (with up to four wires) is used to perform the internal weld, providing high-quality and deep penetration.
7. External Welding: The outer surface of the LSAW (Longitudinal Submerged Arc Welded) steel pipe is welded using a multi-wire submerged arc welding process, ensuring uniformity and strength.
8. Ultrasonic Inspection I: A 100% ultrasonic inspection is carried out on both the internal and external welds, as well as the base metal adjacent to the welds, to identify any potential flaws or inconsistencies.
9. X-ray Inspection I: A 100% X-ray industrial television inspection is performed on the internal and external welds, with image processing systems enhancing detection sensitivity and accuracy.
10. Expansion: The length of the submerged arc straight-seam steel pipe is expanded to improve dimensional accuracy and optimize the distribution of internal stresses within the pipe wall.
11. Hydraulic Pressure Test: After expansion, the steel pipe undergoes a hydrostatic pressure test using a specialized testing machine. The test ensures the pipe can withstand the required pressure, and the machine automatically records and stores all data.
12. Beveling: The ends of the inspected pipe are machined to meet the specified bevel dimensions, preparing it for final connections.
13. Ultrasonic Inspection II: Another round of ultrasonic inspection is conducted to check for any possible defects that may have developed during the diameter expansion and hydraulic pressure test phases.
14. X-ray Inspection II: A second X-ray industrial television inspection is performed on the pipe ends and weld seams after expansion and pressure testing, ensuring complete integrity.
15. Magnetic Particle Inspection: This inspection is carried out at the tube ends to detect any surface or near-surface defects that might have been missed in earlier stages.
16. Anti-corrosion and Coating: Finally, the qualified steel pipe is coated with anti-corrosion materials according to the specific requirements of the customer, ensuring long-term durability and performance in various environments.
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