Seamless steel pipes are pipes with weld seams parallel to the longitudinal axis of the pipe. They are typically categorized into metric electric-welded pipes, thin-walled electric-welded pipes, transformer cooling oil pipes, and so on. The production process for seamless steel pipes is simple, with high efficiency, low cost, and rapid development. Spiral-welded pipes generally have higher strength than seamless pipes, allowing for the production of larger diameter pipes with narrower billets and different diameter pipes with the same width billets. However, compared to pipes of the same length with a straight seam, the length of the weld seam increases, and the production speed is slower.

Seamless steel pipes can be categorized by production process into high-frequency seamless steel pipes and submerged arc welding seamless steel pipes. Submerged arc welding seamless steel pipes are further divided into UOE, RBE, JCOE pipes, etc., based on their different forming methods. Below, we introduce the forming processes of common high-frequency seamless steel pipes and submerged arc welding seamless steel pipes.

Submerged Arc Welding Technique

1. Plate Inspection: Upon entering the production line, the steel plate used to manufacture large-diameter submerged arc weld (SAW) straight seam steel pipes undergoes a full plate ultrasonic inspection first.

2. Milled Edges: Double-sided milling of the steel plate edges using a milling machine to achieve the required width, parallelism of the edges, and bevel shape.

3. Pre-bent Edges: Utilize a pre-bending machine to pre-bend the sheet edges, resulting in curvature that meets the required specifications.

4. Forming: On the JCO forming machine, first half of the pre-bent steel plate is progressively stamped multiple times to form a "J" shape. Then, the other half of the steel plate is similarly bent to create a "C" shape, ultimately forming an open "O" shape.

5. Pre-welding: Join the shaped straight seam welded steel pipes and carry out continuous welding using gas shielded welding (MAG).

6. Inner Welding: Employed longitudinal multi-thread submerged arc welding (up to four threads) for welding on the inner side of straight seam steel pipes.

7. External Welding: Welding is performed on the outer side of straight seam submerged arc steel pipes using longitudinal multi-wire submerged arc welding.

8. Ultrasonic Inspection I: Inspection of the inner and outer weld seams of straight seam steel pipes, as well as the base materials on both sides of the weld seams.

9. X-ray Inspection I: Industrial television X-ray inspection of inner and outer weld seams, utilizing image processing systems to ensure detection sensitivity.

10. Expanding Diameter: Expand the full length of the submerged arc welding straight seam steel pipe to enhance the dimensional accuracy of the pipe and improve the distribution of internal stresses within the pipe.

11. Hydrostatic Test: Each pipe is tested individually on a hydrostatic testing machine to ensure it reaches the required test pressure as per standards, featuring automatic recording and storage capabilities.

12. Deburring: Process the钢管 ends after inspection to achieve the required bevel dimensions.

13. Ultrasonic Inspection II: Conduct ultrasonic inspections individually again to check for any defects that may have occurred in the straight seam welded steel pipes after expansion and hydrostatic testing.

14. X-ray Inspection II: Perform X-ray industrial television inspection and pipe end weld filming on steel pipes after expansion and hydrostatic testing.

15. End of Tube Magnetic Particle Inspection: This inspection is performed to detect any defects at the tube ends.

16. Corrosion Protection and Coating: After qualification, steel pipes are treated with corrosion protection and coated according to customer requirements.

Deoxygenating agent impact

For steel pipes with ω(Als) ≤ 0.01% in straight seam welding, the use of two deoxidizers in VD processing has a minimal effect on the total oxygen content. Both can keep ω(T.O) below 20×10-6; after Si-Al-Ba deoxidation, the total oxygen content in all processes is lower, and the deoxidation effect is stronger than that of Si-Ca deoxidation.

When using two different deoxidizers, Si-Ca and Si-Al-Ba, in the straight seam welded pipe production, there are significant differences in the quantity and size of inclusions during the smelting process. The number of inclusions after Si-Al-Ba deoxidation is less than that after Si-Ca deoxidation, and the sizes are smaller.

When using two different deoxidizers, Si-Ca and Si-Al-Ba, in the straight seam welded pipe process, there is significant secondary oxidation of the molten steel during casting. However, the secondary oxidation of the Si-Al-Ba deoxidized steel is more severe.

The composition of inclusions in forging materials and the content of aluminum inclusions vary significantly. When using Si-Al-Ba deoxidation, the inclusions in the forging are mainly in the form of blocky and chain-like alumina. For straight seam welded pipes using Si-Ca deoxidation, the inclusions in the forging are primarily composite inclusions of silicate-manganese-aluminate. The content of aluminum inclusions in Si-Ca alloy deoxidized forging is less than that in Si-Al-Ba alloy deoxidized forging.