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The manufacturing process of Longitudinal Submerged Arc Welding (LSAW) steel pipes involves several precise steps to ensure the production of high-strength, high-quality pipes. LSAW pipes are made using a longitudinal welding technique, which creates a strong seam along the pipe’s length. Here is a detailed breakdown of the process of LSAW steel pipe.
1. Plate Preparation
The process begins with the selection of steel plates of the desired grade and thickness. These plates are inspected for defects and then trimmed to the required width and shape based on the pipe’s dimensions.
2. Edge Milling
The edges of the steel plates are machined or milled to ensure smooth and uniform surfaces. This step is critical because the quality of the weld depends on the precise alignment and smoothness of the edges.
3. Pre-bending
Before forming the final pipe shape, the steel plate is pre-bent. This involves bending the edges of the plate in preparation for the forming process. Pre-bending ensures the plate can more easily take on the cylindrical shape required for the pipe.
4. Pipe Forming
There are several methods used to form the pipe shape from the flat steel plate. The most common methods for LSAW pipes are:
- UOE Process: The plate is first bent into a "U" shape, then into an "O" shape, followed by an expanding process to achieve the desired dimensions. This method allows for the production of pipes with large diameters.
- JCOE Process: The plate is pressed in multiple steps to form a "J," then a "C," followed by an "O" shape. The "E" step refers to the final expansion of the pipe to achieve the correct diameter and roundness.
5. Tack Welding
After the pipe is formed, it undergoes tack welding to hold the edges together in preparation for the final welding process. This temporary weld ensures that the edges are perfectly aligned and ready for the main weld.
6. Submerged Arc Welding (Internal and External)
The primary welding process in LSAW pipe production is submerged arc welding (SAW), which is performed on both the interior and exterior of the pipe. This welding method uses a continuous arc beneath a layer of flux, which prevents contamination and creates a high-quality weld. The internal weld is performed first, followed by the external weld to complete the seam.
7. Ultrasonic and Radiographic Testing
After welding, the pipe undergoes non-destructive testing (NDT) to ensure the quality and integrity of the weld seam. Ultrasonic and radiographic tests are used to detect any internal or external flaws, such as cracks or voids.
8. Pipe Expansion
The pipe is expanded to improve dimensional accuracy and roundness. This step ensures the final product meets the required specifications for diameter, roundness, and straightness.
9. Hydrostatic Testing
To verify the pipe’s strength and pressure resistance, hydrostatic testing is conducted. The pipe is filled with water and subjected to high internal pressure to check for any leaks or weaknesses in the weld seam or body of the pipe.
10. End Beveling
The pipe ends are beveled to prepare them for welding during installation. This step ensures that the pipe ends can be easily joined with other pipes in the field.
11. Final Inspection and Quality Control
Before the pipes are shipped, they undergo a final inspection to ensure compliance with the required standards. Dimensional checks, surface inspections, and further non-destructive tests are performed to ensure that each pipe meets the necessary specifications.
12. Coating and Finishing (Optional)
Depending on the application, the LSAW pipes may receive additional coatings or linings to protect them from corrosion and environmental damage. Common coatings include epoxy, polyurethane, or polyethylene.
13. Packaging and Shipping
Finally, the pipes are packaged and prepared for transport. Depending on their size and application, they may be bundled or individually wrapped to protect against damage during shipping.
This comprehensive process ensures that LSAW pipes are not only strong and durable but also highly accurate in terms of their dimensions and fit for various demanding industrial applications.
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