Straight seam steel pipe is a steel pipe with welds parallel to the longitudinal direction of the steel pipe. It is usually divided into metric welded steel pipes, welded thin-walled pipes, transformer cooling oil pipes and so on. The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is fast. The strength of spiral welded pipes
is generally higher than that of straight seam welded pipes. Welded pipes with larger diameters can be produced from narrower billets. Welded pipes with different diameters can also be produced with billets of the same width. However, compared with straight seam pipes of the same length, the weld seam length is increased by 30 to 100%, and the production speed is lower. Straight seam steel pipe can be divided into high frequency straight seam steel pipe and submerged arc welded seam steel pipe according to the production process. Submerged arc welded straight seam steel pipes are further divided into UOE
, RBE, JCOE steel pipes according to their different forming methods. The following describes the forming processes of the most common high-frequency straight seam steel pipes
and submerged arc welded straight seam steel pipes.
1. Plate exploration: After entering the production line, steel plates used to manufacture large-diameter submerged arc welded straight seam steel pipes are firstly subjected to full plate ultrasonic inspection;
2. Milling: Double-sided milling of both edges of the steel plate by a milling machine to achieve the required board width, board parallelism and bevel shape;
3. Pre-bent edge: pre-bend the plate with a pre-bending machine, so that the edge of the plate has a curvature that meets the requirements;
4. Forming: On the JCO forming machine, firstly half of the pre-bent steel plate is repeatedly stamped into a "J" shape, and then the other half of the steel plate is similarly bent and pressed into a "C" shape, and finally an opening is formed. "O" shape;
5. Pre-welding: The formed straight seam welded steel pipe is welded and continuously welded by gas shielded welding (MAG);
6. Inner welding: use multi-wire submerged arc welding (up to four wires) for welding inside the straight seam steel pipe;
7. Outer welding: tandem multi-wire submerged arc welding is used on the outside of the LSAW 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: 100% X-ray industrial television inspection of internal and external welds, using image processing system to ensure the sensitivity of flaw detection;
10. Expansion: Expand the diameter of the submerged arc welded straight seam steel pipe to increase the dimensional accuracy of the steel pipe and improve the stress distribution in the steel pipe;
11. Hydraulic test: The steel pipe after diameter expansion is inspected one by one on a hydraulic test machine to ensure that the steel pipe reaches the test pressure required by the standard.
12. Chamfer: Pipe end processing of the steel pipe that passes the inspection to reach the required pipe end bevel size;
13. Ultrasonic inspection Ⅱ: Perform ultrasonic inspection one by one to check the defects that may occur after the diameter expansion and water pressure of straight seam welded steel pipes;
14. X-ray inspection Ⅱ: X-ray industrial television inspection and filming of pipe end welds on steel pipes after diameter expansion and hydraulic pressure test;
15. Tube end magnetic particle inspection: perform this inspection to find tube end defects;
16. Anti-corrosion and coating: qualified steel pipes are anti-corrosion and coated according to user requirements.