Details of Q690D straight seam welded steel pipes commonly used in industrial projects

Q690D straight seam steel pipe: The steel pipes made by hot-rolled steel strip coil welding and straight seam welding on welding equipment are called straight seam welded steel pipes. (The name comes from the fact that the welding part of the steel pipe is in a straight line). It belongs to high-strength welded structural steel. Among them, Q represents yield strength, 690 represents yield strength value, and D represents the grade of steel plate. The impact of the grade D steel plate is -20°C. Q690D can be called low-temperature resistant high-strength steel with a yield strength of 690Mpa.

First, the chemical composition of Q690D straight seam welded steel pipe
Phosphorus: ≤0.025, Sulfur: ≤0.020, Niobium: ≤0.11, Vanadium: ≤0.12, Titanium: ≤0.20, Chromium: ≤1.00, Nickel: ≤0.80, Copper: ≤0.80, Nitrogen: ≤0.015, Molybdenum: ≤0.30, Boron: ≤0.004, Aluminum: ≥0.015;

Second, the mechanical properties of Q690D straight seam welded steel pipe:
Yield strength (MPa): ≥640Mpa; Tensile strength (MPa): ≥730Mpa; Elongation A%: ≥14; Impact energy AKV (J) -20: 47; 180° cold bending test: d=3a

Third, the main production process of Q690D large-diameter straight seam welded steel pipe:
1. Plate inspection: After the steel plates used to manufacture large-diameter submerged arc welded straight seam steel pipes enter the production line, they are first subjected to full plate ultrasonic inspection;
2. Edge milling: The two edges of the steel plate are double-sided milled by the edge milling machine to achieve the required plate width, plate edge parallelism, and groove shape;
3. Pre-bending edge: The plate edge is pre-bent by the pre-bending machine to make the plate edge have the required curvature;
4. Forming: On the JCO forming machine, the first half of the pre-bent steel plate is pressed into a "J" shape through multiple-step punching, and then the other half of the steel plate is bent in the same way to form a "C" shape, and finally an open "O" shape is formed
5. Pre-welding: The formed straight seam welded steel pipe is seamed and continuously welded by gas-shielded welding (MAG);
6. Internal welding: The inner side of the straight seam steel pipe is welded by longitudinal multi-wire submerged arc welding (up to four wires);
7. External welding: longitudinal multi-wire submerged arc welding is used to weld on the outside of the straight seam submerged arc welded steel pipe;
8. Ultrasonic inspection I: 100% inspection of the internal and external welds of the straight seam welded steel pipe and the parent materials on both sides of the weld;
9. X-ray inspection I: 100% X-ray industrial television inspection of the internal and external welds, using an image processing system to ensure the sensitivity of flaw detection;
10. Diameter expansion: The diameter of the submerged arc welded straight seam steel pipe is expanded over the entire length to improve the dimensional accuracy of the steel pipe and improve the distribution of stress inside the steel pipe;
11. Water pressure test: The expanded steel pipes are inspected one by one on a water pressure testing machine to ensure that the steel pipes meet the test pressure required by the standard. The machine has automatic recording and storage functions;
12. Chamfering: The steel pipes that have passed the inspection are processed at the pipe end to achieve the required pipe end groove size;
13. Ultrasonic inspection II: Ultrasonic inspection is performed again on each pipe to check for possible defects in the straight seam welded steel pipe after diameter expansion and water pressure;
14. X-ray inspection II: X-ray industrial television inspection and pipe end weld filming are carried out on the steel pipe after expansion and water pressure test;
15. Magnetic particle inspection of pipe end: This inspection is carried out to find defects at the pipe end;
16. Anti-corrosion and coating: After passing the inspection, the qualified steel pipe is anti-corrosion and coated according to user requirements.

Widely used in coal mining machinery and engineering machinery, such as hydraulic supports, port cranes, flatbed transporters, power towers, various types of cranes, heavy-duty vehicles, oil derricks, high-temperature fans, large electric shovels, dump trucks and drilling rigs, coal mine hydraulic supports, steel structures, etc.