Manufacturing Processes and Treatment Methods for Spiral Tubes

　　 Spiral tube The manufacturing process uses strip steel coils, welding wire, and flux as raw materials. Before being put into service, the spiral pipes must undergo rigorous physical and chemical testing. The butt welding of the strip steel is performed using single‑wire or dual‑wire submerged arc welding, while the back‑welding of the spiral pipe after it has been rolled into a steel tube is carried out by automatic submerged arc welding. Prior to forming, the strip material is subjected to leveling, edge trimming, edge planing, surface cleaning, and specialized processing for transportation and bending. An electric contact pressure gauge is used to regulate the pressure in the cylinders on both sides of the conveyor, ensuring smooth conveyance of the strip steel.

　　External or internal controlled roll forming is employed. A weld‑gap control system is used to ensure that the weld gap meets the requirements of the specific welding process, with strict management of pipe diameter, misalignment, and weld‑gap dimensions. Both internal and external welds are performed using a single‑wire or dual‑wire submerged‑arc welding process on a Lincoln Electric welding machine, thereby achieving stable and reliable welding performance in accordance with established standards. All weld seams undergo continuous online ultrasonic automated flaw detection, ensuring 100% nondestructive testing coverage of the spiral welds. Should any defects be detected, the system automatically triggers an alarm and applies paint markings, enabling operators to promptly adjust process parameters and eliminate defects in a timely manner.

　　Using an air‑plasma cutting machine, the spiral steel pipes are cut into individual lengths. After each batch of pipes has been cut into single‑length sections, their mechanical properties, chemical composition, metallurgical condition, and surface quality must undergo rigorous initial inspection; only after passing nondestructive testing may they proceed to production. The welds are subjected to continuous ultrasonic flaw detection with marked areas, followed by AI‑assisted ultrasonic and X‑ray re‑examination. If defects are detected, they must be repaired and then re‑inspected by nondestructive methods until it is confirmed that all defects have been eliminated.

　　The pipe material at the butt welds of strip steel and at the intersections of D‑shaped joints with spiral‑welded seams shall be inspected by X‑ray fluoroscopy or radiographic film. Each spiral‑welded pipe undergoes a systematic hydrostatic pressure test, with pressure applied using various radial sealing methods. A microcomputer‑controlled hydraulic testing apparatus for spiral‑welded pipes ensures precise control of test pressure and duration, and automatically prints and records all test parameters. Pipe end preparation—including end‑face perpendicularity, bevel angle, and root face—is subject to strict dimensional control.

　　Cleaning can be performed on steel surfaces using various solvents and emulsions to remove oil, grease, dust, lubricants, and other similar organic contaminants. However, these methods cannot eliminate rust, scale, or weld spatter from the processed surface of steel; therefore, they are employed in corrosion‑prevention work only as a supplementary measure. For mechanical derusting, tools such as wire brushes are used to abrade the steel surface, effectively removing loose or flaky scale, rust, and weld slag. Manual tools can achieve a SA2 cleanliness level, while power tools can reach SA3. If the steel surface is covered with tightly adhering iron oxide scales, tool‑based derusting will yield unsatisfactory results and fail to meet the required anchor profile depth for corrosion‑protection applications.

　　Pickling is typically carried out using conventional chemical and electrolytic methods; for pipeline corrosion, only chemical pickling is employed, which can remove scale, rust, and old coatings and is sometimes used as a post‑sandblasting treatment. Chemical cleaning can achieve the required surface cleanliness and roughness, but it produces relatively shallow anchor profiles and may easily lead to contamination of the substrate.

　　Shot blasting and derusting (casting) is a process in which a high‑power motor drives the blasting/casting blades to rotate at high speed, generating centrifugal force that propels abrasive materials—such as steel shot, steel grit, wire segments, and mineral abrasives—onto the concrete‑filled steel pipe. This treatment not only thoroughly removes rust, oxides, and contaminants but also, under the intense impact and friction of the abrasive media, achieves the required surface roughness for spiral‑welded pipes. Following shot blasting or sandblasting, the pipe’s surface exhibits enhanced physical adsorption while the mechanical adhesion between the anti‑corrosion coating and the pipe surface is significantly improved. Consequently, shot blasting and sandblasting represent an ideal method for pipeline derusting. In general, sandblasting is primarily used for treating both the internal and external surfaces of pipelines, whereas shot blasting is typically applied to the exterior surface.