Production process of stainless steel welded pipe

Stainless steel welded pipes, commonly referred to as welded pipes, are manufactured by welding steel strips or coils after they are curled and shaped using forming units and dies. Compared to seamless pipes, welded pipes are produced through a simpler process with higher production efficiency, a wide range of varieties and specifications, and relatively low equipment investment. However, their general strength tends to be lower than that of seamless pipes. This article provides a detailed overview of the stainless steel welded pipe production process.

Stainless Steel Welded Pipe Production Process:

1. Material Preparation:

Raw Material Selection: High-quality stainless steel coils or strips, typically of grades 304, 316, or 321, are chosen.

Slitting: These coils or strips are slit into narrower widths, corresponding to the pipe’s intended size.

2. Pipe Forming:

Uncoiling: The slit stainless steel strips are uncoiled and straightened.

Forming: The flat strips are gradually bent into a cylindrical shape by passing through forming rollers. Various forming methods, such as roll forming, are employed to continuously shape the strip into a round pipe.

3. Welding:

TIG Welding (Tungsten Inert Gas): The edges of the formed strip are welded using TIG welding, ideal for stainless steel as it produces a clean, strong weld while minimizing contamination.

Laser Welding: In some cases, laser welding is used to weld the edges, offering high precision and speed.

Plasma Welding: For thicker materials, plasma arc welding is employed to fuse the edges effectively.

4. Bead Rolling:

After welding, the raised weld bead is rolled to flatten it, making the surface of the pipe smooth and uniform.

5. Heat Treatment (Optional):

Depending on the stainless steel grade and the pipe's application, heat treatment (annealing) may be applied to relieve internal stresses and enhance mechanical properties. The process involves heating the pipe to a high temperature, followed by rapid cooling (quenching).

6. Sizing and Straightening:

Sizing: The pipe passes through sizing rollers to ensure the correct dimensions.

Straightening: The pipe is straightened to eliminate any bends or twists.

7. Surface Treatment:

Pickling and Passivation: The pipe undergoes pickling, an acid bath that removes surface oxides, followed by passivation to form a protective oxide layer that improves corrosion resistance.

Polishing: Pipes requiring a smooth finish are polished to achieve the desired surface roughness.

8. Non-Destructive Testing (NDT):

Various NDT methods, such as ultrasonic testing, eddy current testing, or X-ray inspection, are used to detect defects or inconsistencies in the weld or material.

9. Cutting:

The welded pipe is cut to the specified length using cutting machines or saws.

10. Final Inspection:

The finished pipes are inspected for dimensional accuracy, surface quality, and weld integrity. Pipes not meeting the standards are either reworked or rejected.

11. Packaging and Shipping:

The final products are cleaned, packaged, and prepared for shipment. Protective coverings are applied as necessary to prevent damage during transportation.

This streamlined process ensures that stainless steel welded pipes meet the required specifications and quality standards for various applications.