Production process of stainless steel welded pipe

Stainless steel welded pipes, commonly known as welded pipes, are manufactured by welding steel or steel strips after they are curled and formed using a unit and die. The production process of welded steel pipes is relatively simple, with high production efficiency and a wide range of sizes and specifications. Additionally, welded pipes require lower equipment investment compared to seamless steel pipes. However, welded pipes generally have lower strength than seamless pipes. This article will talk about the production process of stainless steel welded pipe.

Production Process of Stainless Steel Welded Pipe

1. Material Preparation:

Raw Material Selection: High-quality stainless steel coils or strips are selected as the raw material. Common grades include 304, 316, and 321 stainless steel, depending on the required properties.

Slitting: The stainless steel coils or strips are slit into narrower widths based on the required pipe size and specification.

2. Pipe Forming:

Uncoiling: The slit stainless steel strips are uncoiled and straightened to prepare them for the forming process.

Forming: The strip is passed through a series of forming rollers that gradually bend it into a cylindrical shape. The most common forming method is roll forming, where the flat strip is continuously shaped into a round pipe.

3. Welding:

TIG Welding (Tungsten Inert Gas): The edges of the formed strip are welded together using TIG welding, which is preferred for stainless steel due to its ability to produce a clean, strong weld without introducing contaminants.

Laser Welding: In some cases, laser welding is used as an alternative to TIG welding. It uses concentrated laser beams to weld the edges with high precision and speed, making it suitable for high-quality and high-precision applications.

Plasma Welding: This method uses a plasma arc to weld the edges, making it suitable for thicker materials or for pipes with larger wall thicknesses.

4. Bead Rolling:

After the welding process, the weld bead (the raised portion of the weld) is often rolled to reduce its height and make it flush with the pipe surface. This process ensures the pipe maintains a smooth, uniform finish.

5. Heat Treatment (Optional):

Depending on the grade of stainless steel and the intended application, the welded pipe may undergo heat treatment (typically annealing) to relieve internal stresses and improve mechanical properties. The heat treatment process involves heating the pipe to a high temperature and then cooling it rapidly (quenching).

6. Sizing and Straightening:

Sizing: The pipe is passed through sizing rollers to ensure it achieves the correct dimensions, including the internal and external diameter.

Straightening: The pipe is then straightened to eliminate any bends or twists that may have occurred during the forming process.

7. Surface Treatment:

Pickling and Passivation: The pipe undergoes pickling, where it is immersed in acid baths to remove scale, oxides, and other impurities from the surface. After pickling, passivation is carried out to create a protective oxide layer that enhances the corrosion resistance of the pipe.

Polishing: For applications requiring a smooth or aesthetic finish, the pipe may be polished to achieve the desired surface roughness or to meet specific industry standards for surface quality.

8. Non-Destructive Testing (NDT):

The welded pipe undergoes various NDT methods such as ultrasonic testing, eddy current testing, or X-ray inspection to detect any internal or surface defects, including inconsistencies in the weld or material that might affect performance.

9. Cutting:

The welded pipes are cut to the desired lengths using saws or cutting machines. The cutting process ensures the final product meets the length specifications required by the customer or application.

10. Final Inspection:

The final product is subjected to a thorough inspection to verify dimensional accuracy, surface finish, and weld integrity. Pipes that do not meet the required standards are either rejected or reworked as necessary.

11. Packaging and Shipping:

After passing the final inspection, the stainless steel welded pipes are cleaned, packaged, and prepared for shipment. Protective coverings or coatings may be applied to prevent damage during transportation and handling, ensuring that the pipes reach their destination in good condition.