Production process and inspection standards for thick-walled straight seam steel pipes

Thick-walled straight seam steel pipe is a steel pipe made by rolling the long steel strip of the specification into a round pipe through a high-frequency welding unit and welding the straight seam. The shape of the steel pipe can be round, square, or irregular, depending on the sizing and rolling after welding. The main materials of welded steel pipes are 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 large-diameter submerged arc welded thick-walled straight seam steel pipes enters the production line, the first full-plate wave inspection is carried out;
2. Edge milling: double-sided milling on both edges of the steel plate by the edge milling machine to make it meet 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, the first half of the pre-bent steel plate is stamped into a "J" shape by multiple steps, 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 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 on the inside of the thick-walled 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. Lightwave 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 for internal and external welds, using an image processing system 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 check the distribution of the 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 meet the required bevel size of the pipe end;
13. Lightwave inspection Ⅱ: Carry out wave inspection one by one again to check possible defects of straight seam welded steel pipes after diameter expansion and water 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. Magnetic particle inspection at the end of the pipe: Carry out this inspection to find defects at the end of the pipe;
16. Anti-corrosion and coating: The qualified steel pipes are anti-corrosion and coating according to user requirements.

The development of seamless steel pipes focuses on energy-saving and emission-reduction technologies. Thick-walled straight seam steel pipes focus on the development of high-grade (X100) and large-wall thickness (≥60mm) products. The use of overall pipe expansion is the best way to eliminate residual stress for spiral-submerged arc-welded pipes. A reasonable plan, straight seam high frequency welded pipe should take advantage of weld heat treatment.

Thick-walled straight seam steel pipes and spiral steel pipes are a kind of welded steel pipes. They are widely used in national production and construction. Thick-walled straight seam steel pipes and spiral steel pipes have many differences due to different production processes. The difference between straight seam steel pipe and spiral steel pipe.

The production process of straight seam welded pipe is relatively simple. The main production processes are high-frequency welding thick-wall straight seam steel pipe and submerged arc welding thick-wall straight seam steel pipe. Thick-wall straight seam steel pipe has high production efficiency, low cost, and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. The main production process is submerged arc welding. The spiral steel pipe can use the blank of the same width to produce welded pipes with different diameters, and can also use narrower blanks to produce welded pipes with larger diameters. However, compared with thick-walled straight seam steel pipes of the same length, the weld length is increased by 30-100%, and the production speed is lower. Therefore, most of the welded pipes with smaller diameters adopt straight seam welding, and most of the large diameter welded pipes adopt spiral welding. T-welding technology is used in the industry to produce large-diameter thick-walled straight-seam steel pipes, that is, short thick-walled straight-seam steel pipes are butt-jointed again to form a length that meets the needs of the project. The probability of T-welded thick-walled straight-seam steel pipe defects is also greatly improved, and the welding residual stress at the T-shaped weld is relatively large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracks.