The main production process of large diameter longitudinal welded pipe

Longitudinal welded pipes, steel pipes made of hot-rolled or cold-rolled steel plates or steel strip coils welded on welding equipment are called straight seam welded pipes. (It got its name because the welding place of the welded tube is in a straight line).

1. Plate inspection: After the steel plate used to manufacture large-diameter submerged arc welded straight seam steel pipes enters the production line, the entire plate is firstly inspected by ultrasonic;

2. Edge milling: use the edge milling machine to perform double-sided milling on both edges of the steel plate 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 plate so that the edge of the plate has a curvature that meets the requirements;

4. Forming: On the JCO forming machine, first half of the pre-bent steel plate is pressed into a "J" shape through multiple step-by-step stamping. Then bend the other half of the steel plate in the same way, press it into a "C" shape, and finally form an open "O" shape

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

6. Internal welding: use tandem multi-wire submerged arc welding (up to four wires) to weld the inside of the straight seam steel pipe;

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

8. Ultrasonic 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: Conduct 100% X-ray industrial TV inspection on internal and external welds, and use image processing system to ensure the sensitivity of flaw detection;

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

11. Hydrostatic test: On the hydrostatic testing machine, inspect the expanded steel pipes one by one to ensure that the steel pipes meet 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 reach the required pipe end bevel size;

13. Ultrasonic inspection Ⅱ: Conduct ultrasonic inspection one by one again to check possible defects of straight seam welded steel pipes after diameter expansion and hydraulic pressure;

14. X-ray inspection Ⅱ: Carry out X-ray industrial TV inspection and filming of pipe end welds on steel pipes after diameter expansion and hydrostatic test;

15. Tube end magnetic particle inspection: This inspection is carried out to find tube end defects;

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

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