Details of the characteristics, production, and application of Q690ME straight seam welded pipe

As a high-strength low-alloy structural steel material, Q690ME straight seam welded pipe has shown significant advantages in heavy-duty fields such as engineering machinery, bridge construction, and offshore platforms in recent years. This steel achieves a balance between high strength and good welding performance through a special chemical composition design and controlled rolling and controlled cooling process, becoming a breakthrough in domestic production to replace imported similar products. The following analysis is carried out from the aspects of material properties, production process, application scenarios, and market prospects.

First, the material properties and standard system of Q690ME straight seam welded pipe
Q690ME belongs to the high-strength structural steel in the GB/T 1591-2018 standard. The "ME" suffix indicates that it is specially optimized for welding pipes. Its typical chemical composition includes C≤0.12%, Mn≤1.70%, and trace alloy elements such as Nb, V, and Ti. Through fine grain strengthening and precipitation strengthening mechanisms, the yield strength can reach more than 690MPa, and the impact energy at -40℃ is not less than 47J. Compared with ordinary Q690D, the carbon equivalent (Ceq) of Q690ME is controlled below 0.45%, and the welding cold crack sensitivity coefficient (Pcm) is ≤0.25%, which significantly improves the welding performance. A third-party test report shows that the weld zone strength of Q690ME straight seam welded pipe using a submerged arc welding process can reach more than 95% of the parent material, and the hardness of the heat-affected zone is controlled within 280HV, which fully meets the requirements of international standards such as API 5L/ISO 3183.

Second, the core production process breakthrough of Q690ME straight seam welded pipe
1. Plate and coil preparation link: Using TMCP (thermomechanical control process) technology, through two-stage rolling and accelerated cooling, the austenite grain size is refined to 5μm level. The 3800mm wide and thick plate production line put into production by a certain enterprise in 2023 can realize the production of Q690ME steel plates with a thickness of 18-40mm, and the plate shape straightness error is ≤3mm/m.
2. Forming and welding technology: Mainstream manufacturers use the JCOE forming process to form an open tube blank through pre-bending and step-by-step stamping, and then complete the longitudinal seam welding through multi-wire submerged arc welding (usually 4 wires in series). A patent of a Jiangsu enterprise shows that the "step-type heat input control method" it has developed can reduce the width of the welding heat-affected zone to 3.2mm, which is 40% lower than the traditional process.
3. Post-processing process: including diameter expansion (diameter expansion rate 1.0-1.5%), overall heat treatment (580±20℃ tempering), and ultrasonic + eddy current joint flaw detection. It is particularly noteworthy that some companies have introduced the "online quenching + partitioned induction heating" technology to form a uniform bainite structure between the tube body and the weld, and the circumferential deformation can be controlled within 0.15%D.

Third, analysis of typical application scenarios of Q690ME straight seam welded pipes
1. Engineering machinery field: The SY870H excavator boom launched by a certain company in 2024 uses Q690ME straight seam pipes, which reduces the weight of structural parts by 18% and increases the working load to 45 tons. Compared with the original Q550 material solution, the fuel efficiency of the whole machine is increased by 7%.
2. Wind power support structure: In the Yangjiang offshore wind power project in Guangdong, Q690ME steel pipe piles replaced the traditional S355 series, the wall thickness of a single pile was reduced from 95mm to 65mm, and the piling construction period was shortened by 30%. Calculations by a design institute show that this replacement can reduce the cost of the foundation structure by 220,000 yuan per unit.
3. Special vehicle manufacturing: The chassis beam of China National Heavy Duty Truck's new military off-road vehicle uses Q690ME pipes with a specification of Φ219×14mm. The variable cross-section design is achieved through laser welding technology, and the torsional stiffness of the whole vehicle is increased by more than 40%.

Fourth, the market structure and development trend of Q690ME straight seam welded pipes
According to statistics from the China Steel Structure Association, the domestic production capacity of Q690ME straight seam welded pipes has reached 1.2 million tons/ in 2024. It is worth noting that with the development of the trend of "plastic replacing steel", some manufacturers have begun to develop "Q690ME+UHPC" composite pipes, which are lined with ultra-high performance concrete layers to increase the explosion-proof pressure to 45MPa.
Technological development presents three major directions: one is intelligent production; the second is green manufacturing (short process electric arc furnace steelmaking + hydrogen annealing); the third is functional expansion (self-induced crack warning, weather-resistant coating, etc.). Industry experts predict that by 2026, the application of this product in emerging fields such as deep space support and polar equipment will exceed 35%.

The current constraints are mainly reflected in the raw material side: there are less than 5 steel mills in China that can stably supply Q690ME grade coils, and the prices of micro-alloy elements such as Nb and Mo fluctuate greatly. From the perspective of the entire life cycle cost, although the unit price of Q690ME straight seam welded pipe is about 25% higher than that of Q550, its lightweight advantage can reduce the overall use cost by 12-18%. This economy will drive its market share to continue to expand.