Straight seam steel pipes can be divided into high frequency straight seam steel pipes and submerged arc welded straight seam steel pipes according to the production steps. Submerged arc welded steel pipes are divided into UOE, RBE and JCOE steel pipes according to their different forming methods. The following describes the most common forming processes of high-frequency straight seam steel pipes and submerged arc welded straight seam steel pipes.
Submerged arc welding step
1. Board inspection: After the steel plates used to manufacture large-diameter submerged arc welded straight seam steel pipes enter the production line, first, carry out full-plate ultrasonic inspection;
2. Edge milling: Two edges of the steel plate are double-sided milled by an edge milling machine to achieve the required plate width, edge parallelism and groove shape;
3. Pre-bending edge: Pre-bending the edge of the plate with a pre-bending machine to make the edge of the plate have the required curvature;
4. Forming: First, press one half of the pre-bent steel plate into a "J" shape by multiple step stamping on JCO molding machine, then press the other half of the steel plate into a "C" shape by the same bending, and finally form an open "O" shape.
5. Pre-welding: the formed straight seam welded steel pipes are seamed and continuously welded by gas shielded welding (MAG);
6. Internal welding: longitudinal multi-wire submerged arc welding (up to four wires) is used to weld the inside of the straight seam steel pipe;
7. External welding: longitudinal multi-wire submerged arc welding is used to weld outside the longitudinal submerged arc welded steel pipe;
8. Ultrasonic inspection ⅰ: 100% inspection of inner and outer welds and parent materials on both sides of welds of straight seam welded steel pipes;
9.X-ray inspection ⅰ: 100% X-ray industrial television inspection of inner and outer welds, and image processing system to ensure the sensitivity of flaw detection;
10. Expanding: expanding the whole length of submerged arc welded straight seam steel pipe to improve the dimensional accuracy of the steel pipe and improve the distribution of internal stress in the steel pipe;
11. Water pressure test: inspect the expanded steel pipes one by one on a water pressure tester to ensure that the steel pipes meet the test pressure required by the standard, which has the function of automatic recording and storage;
12. Chamfering: processing the pipe end of the steel pipe after passing the inspection to meet the required pipe end groove size;
13. Ultrasonic inspection II: once again, carry out ultrasonic inspection one by one to check the possible defects of straight seam welded steel pipes after diameter expansion and water pressure;
14.X-ray inspection II: X-ray industrial television inspection and tube end weld photography are carried out on the steel pipe after diameter expansion and hydrostatic test;
15. Magnetic particle inspection of pipe ends: conduct this inspection to find the defects of pipe ends;
16. Anticorrosion and coating: qualified steel pipes shall be anticorrosive and coated according to user requirements.
