Stainless steel pipes are widely used in numerous industries such as petrochemicals, construction, food processing, medical care, aerospace, etc., due to their excellent corrosion resistance, high strength, and long service life. Despite their extensive applications, many people have little knowledge of their production and manufacturing process. This article will elaborate on the manufacturing process of stainless steel pipes, helping you fully understand every key step from raw materials to finished products.

Raw Material Preparation

The manufacturing of stainless steel pipes usually starts with stainless steel coils or billets. Different types of steels (such as 304, 316L, 310S, etc.) are selected according to the final application.

• Stainless steel coils: Used for the production of welded pipes.
• Stainless steel billets: Used for manufacturing seamless pipes.

Before entering the production line, raw materials need to undergo surface cleaning, and their chemical composition and mechanical properties are inspected to ensure they meet standards and customer requirements.

Hot Rolling or Cold Rolling Forming

• Welded Pipes:

  • Uncoiling and flattening: Uncoil the stainless steel coil and then perform flattening treatment.
  • Cutting into strips: Cut the entire roll of stainless steel into strips of appropriate width.
  • Forming and rolling: Roll the strips into tubular shapes through roll forming equipment.
  • Automatic welding: Use TIG (tungsten inert gas welding) or laser welding technology for automated welding to form straight-seam stainless steel welded pipes.
  • Weld heat treatment (annealing): Eliminate stress in the welding area, restore the metallographic structure, and improve corrosion resistance.
  • Weld grinding: Grind and polish the outer surface or inner weld to make it smooth and flawless.

• Seamless Pipes:

  • Piercing: Punch holes in the heated stainless steel billet through a piercing machine to form a hollow shell.
  • Hot rolling or cold drawing extension: Process the shell multiple times using hot rolling or cold drawing methods until the required pipe diameter and wall thickness are achieved.

Dimensional Calibration and Straightening

After forming, stainless steel pipes need to undergo dimensional correction and straightening to ensure that the pipe diameter accuracy, roundness, and straightness meet the standards.

• Cold rolling/cold drawing finishing: Further improve dimensional accuracy and surface quality.
• Sizing machine treatment: Unify the outer diameter of the pipes to ensure consistency.

Heat Treatment (Solution Annealing)

Annealing is one of the key steps in the manufacturing of stainless steel pipes. By heating at high temperatures (generally 1040~1150°C) and rapid cooling, internal stress can be eliminated, the uniformity of grains and mechanical properties can be improved, and corrosion resistance can be enhanced.

Pickling and Passivation Treatment

After annealing, an oxide layer will form on the surface of the pipes. Chemical pickling treatment (usually using a mixed solution of nitric acid and hydrofluoric acid) is required to remove the oxide layer.

• Pickling: Remove surface oxides and restore the natural color of stainless steel.
• Passivation: Form a dense and stable passive film on the surface to improve corrosion resistance.

Surface Treatment and Finish Processing

According to customer requirements and different applications, surface treatment methods vary:

• 2B surface: After cold rolling, undergoes heat treatment and pickling, suitable for industrial applications.
• BA surface: Bright annealing treatment, with a mirror-like smooth surface.
• No.4 surface: Mechanically brushed, with strong decorative properties.
• Polishing treatment: Used for sanitary pipes, such as in the food and pharmaceutical industries.

Non-Destructive Testing and Quality Inspection

To ensure the quality of stainless steel pipes, a series of non-destructive testing (NDT) and dimensional inspections are conducted during the production process:

• Eddy current testing: Used to detect surface cracks, inclusions, and other defects.
• Ultrasonic testing: Inspect internal defects.
• Hydrostatic testing: Check the pressure-bearing capacity of the pipes.
• Dimensional inspection: Including length, wall thickness, outer diameter, ovality, etc.

Cutting and Packaging

According to customer requirements, the stainless steel pipes are cut to the specified length. Finally, end processing (chamfering, sealing) and packaging (such as PVC protective film, woven bags, wooden boxes, etc.) are carried out for transportation and storage.

Conclusion

The manufacturing process of stainless steel pipes is a systematic and precise technological chain, where each step is crucial. Whether it is welded pipes or seamless pipes, from raw material selection, forming, heat treatment to testing and packaging, all ensure the excellent performance of stainless steel pipes in various harsh environments. Understanding their manufacturing process not only helps in selecting suitable products but also helps in understanding their value.

If you need high-quality stainless steel pipes, please feel free to contact us for technical support and quotations!