Q690QD straight seam welded steel pipe is a high-strength low-alloy structural steel pipe, that is widely used in bridges, buildings, machinery manufacturing, ships, petrochemicals, and other fields. Its excellent mechanical properties and welding properties make it an indispensable material in modern engineering structures.
First, the material characteristics and standards of Q690QD straight seam welded steel pipe
The core material of Q690QD straight seam welded steel pipe is Q690QD steel plate, and its naming follows the national standard GB/T 16270-2009 "Quenched and Tempered Steel Plate for High Strength Structures". Among them, "Q" represents yield strength, "690" represents yield strength not less than 690MPa, and "QD" indicates that the material has been quenched and tempered (quenched + tempered) and has better low-temperature impact toughness and welding performance.
1. Mechanical properties: The tensile strength of Q690QD can reach 770-940MPa, the elongation is ≥14%, and the low-temperature impact energy at -20℃ is ≥120J, which can meet the structural strength requirements in harsh environments.
2. Chemical composition: By adding micro-alloy elements such as niobium (Nb), vanadium (V), and titanium (Ti), combined with the controlled rolling and controlled cooling process (TMCP), the carbon equivalent (Ceq≤0.47%) is reduced while the strength is improved, significantly improving the weldability.
3. Process adaptability: It supports a variety of welding processes such as submerged arc welding (SAW) and high-frequency welding (ERW). No heat treatment is required after welding to ensure that the weld and the parent material performance match.
Second, the production process and technical points of Q690QD straight seam welded steel pipe
The production process of Q690QD straight seam welded steel pipe mainly includes five links: steel plate pretreatment, forming, welding, finishing, and testing. The key technologies are as follows:
1. Steel plate pretreatment: Ultrasonic flaw detection is used to ensure that the raw materials have no internal defects, and rolling stress is eliminated by the leveling machine.
2. Forming process:
- JCOE forming: The steel plate is gradually bent through multi-step die pressing, with high forming accuracy, suitable for thick-walled (≥20mm) large-diameter steel pipes.
- UOE forming: One-time forming using a hydraulic press is more efficient and suitable for mass production.
3. Welding technology:
- Multi-wire submerged arc welding (up to 4 wires) achieves high-speed welding, uniform penetration, and weld toughness reaches more than 90% of the parent material.
- Argon-rich gas-shielded welding (MAG) is used to reduce pores and improve weld crack resistance.
4. Post-processing and testing:
- Eliminate residual stress and improve dimensional accuracy through the expansion process.
- 100% ultrasonic + X-ray flaw detection, some export products must meet API 5L or EN 10217 standards.
Third, the core application areas of Q690QD straight seam welded steel pipes
1. Heavy machinery: used for key load-bearing components such as engineering machinery booms and mining hydraulic supports, replacing traditional forgings to reduce costs by more than 20%.
2. Bridge engineering: For example, the Shanghai-Nantong Yangtze River Bridge uses Q690QD straight seam welded steel pipes as bridge tower segments, reducing weight by 15% while improving seismic performance.
3. Offshore platform: A seawater corrosion-resistant version (adding Cu and Cr elements) is used for conductor frame nodes, with a service life of 30 years.
4. New energy field: Q690QD steel pipes are used in the connection section of wind power towers, which can increase the tower height by 10%-15% compared to Q620 materials.
Fourth, the market status and development trend of Q690QD straight seam welded steel pipes
According to data from the China Iron and Steel Association, the market size of Q690 high-strength steel pipes in 2024 has exceeded 800,000 tons, with an annual growth rate of 12%. Future development directions include:
1. Lightweight demand: New energy vehicle battery pack structural parts try to use thin-walled Q690QD welded pipes, which are 30% lighter than traditional solutions.
2. Green manufacturing: The hydrogen reduction steelmaking process developed by Baowu Group can reduce the carbon footprint of Q690QD by 40%.
3. Intelligent production: Anshan Iron and Steel Bayuquan Base has built the world's first Q690QD straight seam pipe intelligent production line, achieving a 72-hour rapid response from order to delivery.
Fifth, the purchase and use recommendations of Q690QD straight seam welded steel pipes
1. Certification verification: Give priority to products that have passed international certifications such as CE and ABS, and exports to the EU must meet the requirements of the PPE directive.
2. Welding process qualification (PQR): It is recommended to use GB/T 19869.1 standard for welding process verification, especially for thick plate (>30mm) T-joints.
3. Anti-corrosion matching: The three-layer anti-corrosion system of "epoxy powder + polypropylene tape" is recommended for marine environments, and the anti-corrosion life can reach 50 years.
Q690QD straight seam welded steel pipe will continue to break through the performance boundaries in material upgrading and process innovation and provide key material support for the transformation of China's manufacturing to high-end. In the next 3-5 years, with the popularization of new technologies such as TMCP+online quenching, the cost of Q690QD steel pipe is expected to drop by 15%-20%, further expanding its application space in emerging fields such as municipal pipe corridors and modular buildings.
