I. Main process flow of hot-rolled seamless steel tubes
1. Billet preparation and inspection: High-quality carbon steel or alloy steel round billets are selected and undergo strict inspection to ensure they are free of surface cracks, inclusions, and other defects.
2. Heating: The billet is fed into an annular heating furnace and heated to 1100~1250℃ to give it good plasticity, facilitating subsequent piercing.
3. Piercing: The heated billet is passed through a two-roll skew piercing mill (such as a Mennesmann piercing mill). Under the combined action of the rolls and the mandrel, the solid billet is rolled into a hollow tube. This is a crucial step in forming a "seamless" structure.
4. Rolling and stretching: The tube is fed into a tube rolling mill (such as a continuous tube rolling mill or a three-roll tube rolling mill) for multi-pass rolling to further reduce wall thickness and increase diameter, controlling the accuracy of outer diameter and wall thickness.
5. Sizing and Reduction: A sizing machine or tension reducing machine is used to precisely adjust the outer diameter of the steel pipe, ensuring that dimensional tolerances meet standard requirements. Some units can achieve high-precision control of ±0.2%.
6. Heat Treatment: Normalizing, annealing, or quenching and tempering treatments are performed according to material requirements to improve the microstructure and enhance mechanical properties.
7. Cooling and Straightening: After natural cooling on a walking beam cooling bed, the steel pipe is straightened to eliminate bends and ensure straightness.
8. Finishing and Inspection: Substandard portions at the beginning and end are removed. Manual dimensional measurements are performed, and non-destructive testing (such as ultrasonic testing and eddy current testing), hydrostatic testing, and metallographic analysis are conducted to ensure quality before warehousing.
II. Cold Rolled/Cold Drawn Seamless Steel Pipe Process (For High-Precision Products)
Suitable for small-diameter, thin-walled steel pipes with high precision requirements, typically using hot-rolled pipes as raw materials:
Pickling and Lubrication → Removes oxide scale and lubricates the surface.
Cold Rolling or Cold Drawing → Drawing or rolling at room temperature using dies to improve dimensional accuracy and surface finish.
Annealing Treatment → Eliminates work hardening and restores plasticity.
Straightening, Finishing, and Inspection → Same process as hot rolling, but with stricter inspection standards.
These steel pipes have a brighter surface and uniform wall thickness, and are commonly used in hydraulic systems, precision machinery, and other fields.
III. Extrusion Method (Suitable for High-Strength Alloy Steel)
The heated billet is placed in a closed extrusion cylinder, and high pressure is applied through a punch, causing the metal to be extruded from the die orifice. Suitable for producing small-diameter, difficult-to-deform alloy steel pipes, such as stainless steel and high-temperature alloy pipes.
IV. Key Quality Control Points
Perforation Quality: Directly affects the uniformity of capillary wall thickness
Dimensional Accuracy: Relies on real-time monitoring by a laser diameter measurement system
Non-destructive Testing: Eddy current testing sensitivity can reach 0.1mm×1mm defect detection
Physical and Chemical Testing: Includes Brinell hardness testing, impact testing, spectral composition analysis, etc.
