Seam treatment of spiral welded pipe

The seam treatment of spiral welded pipes is a crucial process that ensures the integrity, strength, and durability of the welded joint. Here are the main steps involved in the seam treatment of spiral welded pipes.

1. Weld Preparation

Edge Milling: The edges of the strip steel are milled to form the correct bevel angle for welding.

Cleaning: The edges are cleaned to remove any dirt, oil, or rust that might affect the quality of the weld.

2. Welding Process

Submerged Arc Welding (SAW): Spiral welded pipes are typically welded using the submerged arc welding process. This involves the use of flux to create a slag layer that protects the weld from contamination.

Double-Wire Double-Sided Welding: The welding is performed on both the inner and outer surfaces of the pipe, usually with two wires, to ensure a strong and uniform weld.

3. Seam Inspection and Testing

Visual Inspection: Initial visual inspection to check for any obvious defects such as cracks or incomplete fusion.

Nondestructive Testing (NDT): Techniques such as ultrasonic testing, radiographic testing, and magnetic particle inspection are used to detect internal and surface defects in the weld seam.

Hydrostatic Testing: The welded pipe is filled with water and subjected to high pressure to ensure the seam can withstand the required pressure without leaking.

4. Post-Weld Heat Treatment (PWHT)

Stress Relieving: The welded seam is heated to a specific temperature and then gradually cooled to relieve residual stresses that may have developed during the welding process.

Normalization: The pipe may be heated to a temperature above its critical range and then air-cooled to refine the grain structure and enhance the mechanical properties.

5. Grinding and Smoothing

Grinding: Any excess weld material or slag is ground off to ensure a smooth and even surface.

Smoothing: The weld area is further smoothed to ensure there are no sharp edges or rough surfaces that could cause issues during the pipe’s use or coating.

6. Coating and Corrosion Protection

Surface Preparation: The pipe surface, including the welded seam, is cleaned and prepared for coating.

Coating Application: Anti-corrosion coatings such as epoxy, polyethylene, or other protective materials are applied to the seam and the rest of the pipe to protect it from environmental factors and prolong its lifespan.

7. Final Inspection

Dimensional Check: Ensuring the pipe meets all specified dimensions and tolerances.

Quality Certification: A final inspection report is generated, and the pipe is certified as meeting all quality standards before being shipped to the customer.

By following these meticulous seam treatment steps, manufacturers can ensure that spiral welded pipes have high structural integrity, excellent performance, and a long service life.