Spiral steel pipe is a large-diameter steel pipe made from steel coils through a spiral forming process. It is widely used in fluid transportation pipeline projects in the oil, gas, chemical, and water conservancy sectors. The production process primarily involves key steps such as raw material preparation, strip leveling and shearing, forming, welding, weld seam treatment, and testing and quality inspection. Each step directly impacts the quality and performance of the final product.
1. Raw Material Preparation
The primary raw material for spiral steel pipe is hot-rolled or cold-rolled steel coils, typically made from carbon structural steels such as Q235B and Q345B, or low-alloy high-strength steel. Prior to production, the steel coils undergo rigorous quality inspections, including chemical composition analysis, mechanical property testing (such as tensile strength and elongation), and surface defect inspection (such as cracks, scale, and folds) to ensure compliance with relevant standards (such as GB/T 9711 and API 5L).
2. Strip Leveling and Shearing
Because the strip may bend or undulate during transportation or rolling, it must be leveled in a leveler to ensure that the strip meets forming requirements. Subsequently, depending on the specifications of the spiral steel pipe, the strip is sheared to the desired length using a flying shear or circular shear to ensure continuity during subsequent forming.
3. Spiral Forming
Forming is the core step in spiral steel pipe production. The strip is gradually coiled into a spiral tube by a forming machine (usually an externally or internally controlled roller forming machine) during continuous welding. The forming machine's rollers are adjusted at a specific angle (usually 1.5° to 3°) to gradually bring the strip edges together and form a stable spiral. During the forming process, strip tension, speed, and roller pressure must be strictly controlled to ensure the tube's roundness, straightness, and uniform weld gap.
4. Welding Process
Spiral steel pipes are typically welded using submerged arc welding (SAW), which is divided into two steps: internal welding and external welding.
Internal welding: Single-wire or twin-wire SAW is used to weld the root of the weld inside the pipe to ensure penetration and penetration.
External welding: Multi-wire SAW (usually twin or triple wires) is used on the outside to improve welding efficiency and ensure weld strength and appearance.
Welding parameters (such as current, voltage, and speed) must be precisely adjusted according to the strip thickness and material to avoid defects such as porosity, slag inclusions, and lack of fusion. Some high-end spiral steel pipes also utilize a pre-welding + finishing process, first using high-frequency pre-welding to secure the weld, followed by submerged arc welding for the final weld.
5. Weld Seam Treatment
After welding, the weld seam requires finishing and inspection:
Weld seam grinding: This removes weld excess, creates a smooth transition between the weld and the base material, and reduces stress concentrations. Ultrasonic Testing (UT): Inspects welds for internal defects (such as pores and cracks).
X-ray Testing (RT): Performs non-destructive testing of critical areas to ensure weld quality meets standards.
6. Expansion and Straightening
To eliminate welding stress and improve dimensional accuracy, spiral steel pipes typically undergo expansion (hydraulic or mechanical expansion of the pipe body). They are then straightened to ensure they meet project installation requirements.
7. End Processing and Inspection
Depending on customer requirements, the ends of spiral steel pipes may require beveling (for welding) or flattening (for flange connections). Finally, the pipes undergo rigorous quality inspections, including:
Dimensional inspection (outer diameter, wall thickness, and ovality);
Pressure testing (water or air pressure testing to verify pressure resistance);
Anti-corrosion treatment (such as epoxy powder coating or 3PE coating to improve corrosion resistance).
8. Labeling and Shipment
Qualified spiral steel pipes are labeled according to standards (such as material, specifications, and production batch number) and packaged or stacked before shipment to the project site for installation and use.
Conclusion
The production process for spiral steel pipes involves numerous precision steps, and rigorous quality control is required from raw materials to finished product. Technological advancements, including the application of automated forming, intelligent welding, and non-destructive testing, have further improved the manufacturing efficiency and reliability of spiral steel pipes, making them an indispensable material in modern pipeline engineering.
