Review
Steel pipes with a straight seam are typically categorized into two main types: high-frequency electric welded (HFW) and submerged arc welded (SAW). Among SAW pipes, there are different forming methods such as UOE, RBE, and JCOE. This article provides an overview of the most common manufacturing processes for both high-frequency and submerged arc welded steel pipes.
Submerged Arc Welding Process
1. Plate Inspection: Before entering the production line, the steel plate used for large-diameter SAW pipes undergoes full-length ultrasonic testing to 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 required width, parallelism, and groove shape.
3. Pre-Bending: A pre-bending machine is used to give the edges of the steel plate the necessary curvature before further processing.
4. Forming: On the JCO forming machine, one half of the pre-bent steel plate is pressed into a "J" shape, while the other half is shaped into a "C." Finally, the two halves are joined to form an "O" shape.
5. Pre-Welding: After forming, the pipe is pre-welded using gas-shielded metal arc welding (MAG) to ensure a stable joint before final welding.
6. Internal Welding: The inside of the pipe is then welded using multi-wire submerged arc welding, which can involve up to four wires for enhanced quality and efficiency.
7. External Welding: Similarly, the outer surface of the pipe is also welded using longitudinal multi-wire submerged arc welding 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.
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 flaw detection sensitivity.
10. Diameter Expansion: The entire length of the SAW pipe is expanded to improve dimensional accuracy and optimize stress distribution within the pipe wall.
11. Hydraulic Test: After expansion, the pipe is tested on a hydraulic testing machine to ensure it meets the required pressure standards. The system automatically records and stores test results.
12. Beveling: Once passed, the ends of the pipe are beveled to meet specified groove dimensions for future connections.
13. Ultrasonic Inspection II: A second ultrasonic check is carried out to detect any defects that may have occurred during straightening or hydrostatic testing.
14. X-Ray Inspection II: The pipe is again inspected using X-ray industrial TV, with special attention given to the end welds after expansion and hydrostatic testing.
15. Magnetic Particle Inspection: This step is used to identify any surface defects at the pipe ends.
16. Corrosion Protection and Coating: Finally, the qualified steel pipe is coated or protected according to the customer's specifications to ensure long-term durability and performance in various environments.
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