Review
Steel pipes with straight seams are typically categorized into two main types: high-frequency welded and submerged arc welded. Among these, submerged arc welded steel pipes are further divided based on their forming methods, such as UOE, RBE, and JCOE. This article outlines the most commonly used manufacturing processes for both high-frequency and submerged arc welded straight seam steel pipes.
Submerged Arc Welding Process
1. Plate Inspection: Before entering the production line, the steel plates used for large-diameter submerged arc welded pipes undergo a full-length ultrasonic test to ensure quality and detect any internal flaws.
2. Edge Milling: The edges of the steel plate are milled on both sides using an edge milling machine to achieve the desired width, parallelism, and groove shape.
3. Pre-bending: A pre-bending machine is used to curve the edges of the steel plate, preparing them for the next stage of forming.
4. Forming: On a JCO forming machine, the pre-bent steel plate is first pressed into a "J" shape, then into a "C" shape, and finally into an "O" shape, creating the final pipe structure.
5. Pre-welding: After forming, the pipe is joined and continuously welded using gas shielded metal arc welding (MAG).
6. Internal Welding: The inside of the steel pipe is welded using multi-wire submerged arc welding, which can involve up to four wires for enhanced strength and consistency.
7. External Welding: The outer surface of the pipe is also welded using a similar multi-wire submerged arc welding process to ensure structural integrity.
8. Ultrasonic Inspection I: A comprehensive ultrasonic test is conducted on both the inner and outer welds, as well as the base metal adjacent to the weld, ensuring no defects are present.
9. X-ray Inspection I: An X-ray industrial TV inspection is performed on the internal and external welds, utilizing image processing systems to enhance detection accuracy.
10. Diameter Expansion: The entire length of the pipe is expanded to improve dimensional accuracy and optimize stress distribution within the pipe wall.
11. Hydraulic Test: After expansion, the pipe undergoes a hydraulic test on a dedicated testing machine to confirm it meets the required pressure standards. The system automatically records and stores all data.
12. Beveling: Once the pipe passes inspection, the ends are beveled to meet the specified groove dimensions for future connections.
13. Ultrasonic Inspection II: A second ultrasonic check is performed after straightening and hydrostatic testing to identify any potential defects that may have developed during the process.
14. X-ray Inspection II: A final X-ray inspection is carried out, including filming of the tube end welds, to ensure complete weld integrity.
15. Magnetic Particle Inspection: This step is used to detect any surface or near-surface defects at the pipe ends.
16. Anti-corrosion and Coating: Finally, the qualified pipe is coated or protected according to the customer's specifications, ensuring long-term durability and performance in various environments.
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