Introduction to the production process and inspection standards of thick-walled straight seam steel pipes

The thick-walled straight seam steel pipe is a steel pipe made by rolling the long steel strip of the specification into a round tube shape and welding the straight seam by a high-frequency welding unit. The shape of the steel pipe can be round, square, or special, it depends on the sizing rolling after welding. The materials of welded steel pipes are mainly: low carbon steel and low alloy steel or other steel with σs≤300N/mm2, and σs≤500N/mm2. The production process of thick-walled straight seam steel pipe is as follows:

1. Plate inspection: After the steel plate used to manufacture the large-diameter submerged arc welded thick-walled straight seam steel pipe enters the production line, the first full plate wave inspection is performed;

2. Edge milling: Double-sided milling is performed on both edges of the steel plate by an edge milling machine to achieve the required plate width, plate edge parallelism, and groove shape;

3. Pre-bending: use a pre-bending machine to pre-bend the edge of the board, so that the edge of the board has the required curvature;

4. Forming: On the JCO forming machine, firstly, half of the pre-bent steel plate is pressed into a "J" shape through multiple step-by-step stamping, and then the other half of the steel plate is also bent into a "C" shape, and finally formed Open "O" shape

5. Pre-welding: make the formed straight seam welded steel pipe joint and use gas shielded welding (MAG) for continuous welding;

6. Internal welding: use longitudinal multi-wire submerged arc welding (mostly four wires) to weld on the inner side of the thick-walled straight seam steel pipe;

7. External welding: use longitudinal multi-wire submerged arc welding to weld on the outside of the straight seam submerged arc welded steel pipe;

8. Wave inspection I: 100% inspection of the inner and outer welds of the straight seam welded steel pipe and the base metal on both sides of the weld;

9. X-ray inspection I: 100% X-ray industrial TV inspection is performed on the internal and external welds, and an image processing system is used to ensure the sensitivity of flaw detection;

10. Diameter expansion: Expand the full length of the submerged arc welded thick-walled straight seam steel pipe to improve the dimensional accuracy of the steel pipe and the distribution of the internal stress of the steel pipe;

11. Hydraulic test: On the hydraulic testing machine, the expanded steel pipe is tested one by one to ensure that the steel pipe meets the test pressure required by the standard. The machine has automatic recording and storage functions;

12. Chamfering: Process the pipe end of the qualified steel pipe to meet the required groove size of the pipe end;

13. Wave inspection II: wave inspection is carried out one by one again to check the possible defects of the straight seam welded steel pipe after diameter expansion and water pressure;

14. X-ray inspection II: X-ray industrial TV inspection and pipe end weld filming are performed on the steel pipe after expansion and hydrostatic test;

15. Pipe end magnetic particle inspection: carry out this inspection to find pipe end defects;

16. Anti-corrosion and coating: The qualified steel pipes are anti-corrosion and coated according to user requirements.