What are the technological details of spiral welded steel pipe manufacturing

The production process of spiral welded steel pipe is complex and meticulous, requiring multiple procedures to ensure product quality and performance. The following is a detailed introduction to the process:

First, Raw Material Preparation and Inspection of Spiral Welded Steel Pipe
1. Raw Material Selection: Using strip steel coils as the main raw material, appropriate materials (such as Q235, Q345, X42-X80 steel grades, etc.) and specifications are selected according to different applications. Supporting materials include welding wire (such as H08A, H10Mn2) and flux (such as HJ431), which must meet welding process requirements.
2. Quality Inspection of Spiral Welded Steel Pipe: The chemical composition (carbon, silicon, manganese, sulfur, phosphorus, etc.) and mechanical properties (tensile strength, yield strength, elongation) of the strip steel are tested to ensure that the raw materials meet standards.

Second, Strip Steel Pretreatment of Spiral Welded Steel Pipe
1. Leveling and Edge Trimming: A leveling machine is used to eliminate bending and wavy deformation of the strip steel, making its surface smooth. Trimming: The trimming machine removes burrs, cracks, or irregularities from the strip steel edges to ensure neat edges.
2. Shearing and Surface Cleaning: The shearing machine processes the strip steel edges to form the bevels required for welding (such as V-shaped or X-shaped bevels), facilitating subsequent welding fusion. Shot blasting or sandblasting is used to clean the strip steel surface of oxide scale, oil stains, and other impurities to avoid affecting weld quality.
3. Pre-bending: The pre-bending machine initially bends the strip steel edges to meet the curvature requirements of spiral forming, reducing stress concentration during subsequent forming.

Third, Spiral Forming of Spiral Steel Pipes
1. Strip Steel Conveying and Positioning: An electric contact pressure gauge controls the pressure of the hydraulic cylinders on both sides of the conveyor to ensure smooth strip steel transport and avoid deviation or wrinkling.
2. Roll Forming: An externally or internally controlled roller forming device gradually rolls the strip steel into a spiral tube blank. During the forming process, the diameter and roundness of the tube blank are controlled by adjusting the position and pressure of the roller group.
3. Weld Gap Control: A weld gap control device is used to monitor and adjust the weld gap of the pipe blank in real time (generally controlled within 0.5-1.5mm), while ensuring that the misalignment does not exceed the specified value (e.g., ≤1mm) to meet welding requirements.

Fourth, Welding Process of Spiral Steel Pipes
1. Double-Sided Submerged Arc Welding of Spiral Steel Pipes
Inner Welding: After the pipe blank is formed, the inner wall is welded first, using single-wire or double-wire submerged arc welding. The welding wire is fed from inside the pipe, and the flux covers the weld, achieving fusion under the action of the arc.
Outer Welding: After the inner welding is completed, the outer wall of the pipe blank is welded. The process is similar to that of the inner welding, ensuring that both the inner and outer welds achieve high strength and high sealing performance.
Advantages: Submerged arc welding has concentrated heat, large penetration depth, beautiful weld formation, reduces defects such as porosity and slag inclusions, and provides stable welding quality.
2. Butt Weld Repair of Spiral Steel Pipes
When butt-welding the strip ends, single-wire or double-wire submerged arc welding is first used. After rolling into a steel pipe, the butt weld is then repaired using automatic submerged arc welding to ensure the continuity of the entire pipe body.

Fifth, Quality Inspection and Defect Handling of Spiral Steel Pipes
1. Online Ultrasonic Testing of Spiral Steel Pipes: Completed welds are inspected 100% using an online continuous ultrasonic automatic flaw detector. When defects such as cracks or incomplete penetration are found, an automatic alarm is triggered, and a mark is sprayed for easy subsequent processing.
2. X-ray Inspection of Spiral Steel Pipes: All butt welds of the strip and sections containing T-joints intersecting with the spiral weld are inspected using X-ray television or radiography to further confirm internal defects.
3. Defect Repair of Spiral Steel Pipes: For detected defects, manual ultrasonic and X-ray re-examination is used to locate the defects before repair (e.g., grinding, welding). After repair, non-destructive testing is repeated until the pipe passes inspection.

Sixth. Physical Performance Testing of Spiral Steel Pipes
1. Hydrostatic Pressure Test: Each spiral steel pipe must undergo a hydrostatic pressure test. The pressure is applied through a radial sealing device. The test pressure is determined according to the pipe specifications and standards (e.g., formula P=2ST/D, where P is the test pressure, S is the wall thickness, T is the yield strength, and D is the outer diameter). The pressure holding time should not be less than the specified value (e.g., 5-10 seconds) to ensure no leakage. Test parameters are automatically recorded and printed by a computerized hydrostatic testing device.
2. Mechanical Performance Testing of Spiral Steel Pipes: Each batch of steel pipes undergoes an initial inspection, testing the tensile strength, yield strength, impact toughness, and other mechanical properties of the weld, as well as chemical composition analysis, to verify the reliability of the pipe manufacturing process.

Seventh. Cutting and End Treatment of Spiral Steel Pipes
1. Fixed-Length Cutting of Spiral Steel Pipes: Continuous steel pipes are cut into single pieces using an air plasma cutting machine. The length is determined according to requirements (e.g., 6 meters, 12 meters). The cut end face must be flat.
2. Pipe End Machining of Spiral Steel Pipes: Pipe ends are machined using turning, milling, and other machining processes to precisely control end face perpendicularity (error ≤1mm), bevel angle (e.g., 30°±5°), and blunt edge dimensions (e.g., 1-2mm), facilitating subsequent pipe connections (e.g., welding, flange connections).

Eighth. Surface Treatment and Packaging of Spiral Steel Pipes
1. Surface Corrosion Protection of Spiral Steel Pipes: Depending on the operating environment, the steel pipes undergo anti-corrosion treatment (e.g., coating with epoxy coal tar pitch, three-layer PE coating, etc.) to prevent corrosion and extend service life.
2. Marking and Packaging of Spiral Steel Pipes: Specifications, material, standard number, production batch number, etc., are sprayed onto the steel pipe surface for easy traceability. Pipes are stacked according to specifications and protected by bunding or wrapping to prevent damage during transportation.
3. Summary of the Technological Characteristics of Spiral Steel Pipes
High Efficiency of Spiral Steel Pipes: Large-diameter steel pipes can be produced using narrower steel strips, resulting in high production efficiency and suitability for mass production.
The flexibility of spiral welded steel pipes: By adjusting the forming and welding parameters, they can meet the production needs of steel pipes with different diameters, wall thicknesses, and materials.
The high reliability of spiral welded steel pipes: Multiple testing processes (ultrasonic, X-ray, and hydrostatic testing) ensure the quality of the steel pipes, making them suitable for high-pressure and high-risk working conditions (such as oil and gas pipelines and urban water supply trunk lines).