The production process of spiral welded pipes involves a series of precise and well-controlled steps to ensure the quality and structural integrity of the final product. The process begins with the selection of raw materials, including steel strip coils, welding wire, and flux, which undergo rigorous physical and chemical testing before being used in production.
Next, the ends of the steel strip are joined using single or double wire submerged arc welding. After the strip is formed into a pipe, any imperfections are repaired using automatic submerged arc welding to maintain the quality of the seam. Before forming, the steel strip is leveled, trimmed, planed, cleaned, and pre-bent to prepare it for the rolling process.
An electric contact pressure gauge is used to regulate the pressure on both sides of the conveyor system, ensuring smooth and consistent feeding of the strip. The forming process can be either externally or internally controlled using roll forming techniques. A weld gap control device ensures that the gap between the edges of the strip meets the required specifications, while also maintaining accurate control over the pipe diameter and alignment.
Both internal and external welding operations are performed using American Lincoln welding machines, employing either single or double wire submerged arc welding methods to achieve consistent and reliable weld quality. All weld seams are inspected in real-time using an online continuous ultrasonic automatic flaw detection system. This system ensures full coverage of non-destructive testing for spiral welds, automatically alerting operators when defects are detected and marking them for correction. Production staff can then adjust parameters promptly to eliminate any issues.
Once the pipe is formed, it is cut into individual sections using an air plasma cutting machine. After cutting, each batch of pipes undergoes a comprehensive first inspection, checking mechanical properties, chemical composition, weld fusion, surface quality, and non-destructive testing results. Only after passing these checks is the production officially approved.
Pipes with weld marks from ultrasonic testing are manually re-inspected using ultrasonic waves and X-ray imaging. Any confirmed defects are repaired and retested until all flaws are completely removed. Additionally, areas where the butt weld intersects with the spiral weld are inspected using X-ray television or filming to ensure there are no hidden issues.
Each pipe is subjected to a hydrostatic pressure test, during which the pipe is sealed radially. The test pressure and duration are precisely controlled by a microcomputer-based water pressure detection system, and the test results are automatically printed and recorded for documentation. Finally, the pipe ends are machined to ensure accurate verticality, proper bevel angle, and correct edge preparation, meeting all required specifications.
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