Some key points about spiral welded steel pipes

　　 Spiral steel pipe It is a spiral‑seam steel pipe manufactured from rolled strip steel, formed by cold extrusion and welded using an automated double‑wire, double‑sided submerged‑arc welding process. In the production of spiral steel pipes, the strip steel is fed into the pipe‑welding line. After being passed through a series of rollers, the strip gradually coils to form a circular tube blank with an open seam. By adjusting the downward pressure of the extrusion rollers, the weld gap is maintained within 1–3 mm, and the ends of the joint are brought into flush alignment.

　　(1) The raw materials for spiral welded steel pipes are coil stock, welding wire, and flux. Prior to use, these materials must undergo rigorous physical and chemical testing.

　　(2) The end-to-end joints of the steel strip shall be welded using single-wire or double-wire submerged arc welding, and after coiling into a steel pipe, automatic submerged arc welding shall be employed for repair welding.

　　(3) Prior to forming the spiral steel pipe, the strip steel undergoes leveling, trimming, planing, surface cleaning, transportation, and pre-bending.

　　(4) The electrical contact pressure gauge is used to regulate the pressure of the clamping cylinders on both sides of the conveyor, ensuring smooth strip steel conveyance.

　　(5) Employ either external or internal roller pressing for forming.

　　(6) A weld gap control device is employed to ensure that the weld gap meets welding requirements, with strict control over pipe diameter, misalignment, and weld gap.

　　(7) Both the internal and external welds of the spiral steel pipe are performed using Lincoln electric welding machines with either single‑wire or dual‑wire submerged arc welding, ensuring consistent weld quality.

　　(8) All weld seams are inspected using an online, continuous ultrasonic automatic flaw detector, ensuring 100% coverage of nondestructive testing for spiral welds. If defects are detected, the system automatically triggers an alarm and applies a marking, enabling production personnel to adjust process parameters at any time and promptly eliminate the defects.

　　(9) Use an air plasma cutter to cut the steel pipes into individual pieces.

　　(10) After each batch of spiral welded pipes is cut into individual lengths, a rigorous first‑article inspection is conducted to verify the pipe’s mechanical properties, chemical composition, weld quality, surface finish, and nondestructive testing results. Production may commence only upon confirmation that the manufacturing process meets all specified requirements.

　　(11) After manual ultrasonic and X-ray re-inspections, if defects are detected in welds marked by continuous ultrasonic testing, the affected areas shall be repaired and subjected to nondestructive testing again until it is confirmed that all defects have been eliminated.

　　(12) Both the butt welds of strip steel and the T-joints where they intersect with spiral welds shall be inspected by X-ray television or radiographic film.

　　(13) Each steel pipe shall undergo a hydrostatic pressure test with radial sealing. The microcomputer‑controlled hydrostatic testing apparatus ensures precise control of test pressure and duration. Test parameters are automatically printed and recorded.

　　(14) Machine the pipe ends to precisely control end-face perpendicularity, bevel angle, and edge chamfer.

　　According to the quality inspection results of spiral welded steel pipes, they are generally classified into three categories:合格品 (qualified products), 返修品 (repaired products), and 废品 (scrap). Qualified products are those whose external and internal qualities meet the relevant standards or the technical requirements for delivery and acceptance. Repaired products are those whose external and internal qualities do not fully comply with the standards and acceptance criteria but may be repaired and, after repair, can meet such standards and criteria. Scrap refers to products whose external and internal qualities fail to meet the required standards and cannot be repaired, or whose repaired condition still does not satisfy the standards and acceptance conditions.