As a representative product of low-alloy high-strength structural steel, Q390GJB straight seam welded steel pipes are widely used in construction, bridges, machinery manufacturing, and other fields. Although these two sheets of steel belong to the Q390 series, they differ in chemical composition, mechanical properties, implementation standards, and applicable scenarios, and require professional analysis from multiple dimensions.

First, the material properties and standard differences of Q390GJB straight seam welded steel pipes
Q390GJB and Q390GJC are both low-alloy high-strength structural steels under the GB/T 1591-2018 standard, but their core differences are reflected in the implementation standards:
1. Q390GJB follows the "GB/T 3091-2015 Welded Steel Pipe for Low-Pressure Fluid Transportation" standard, which is mainly used to transport low-pressure fluids such as water and gas. The carbon content in its chemical composition is controlled below 0.20%, the manganese content is 1.00%-1.60%, and micro-alloy elements such as niobium and vanadium are added to improve strength. Yield strength ≥390MPa, tensile strength 490-670MPa, elongation ≥20%.
2. Q390GJC complies with the standard of "GB/T 13793-2016 Straight Seam Electric Welded Steel Pipe", which is more suitable for load-bearing scenarios such as building structure support and mechanical parts. The content of harmful elements such as phosphorus and sulfur is more stringent (P≤0.030%, S≤0.025%), and the impact energy must reach 34J (0℃ low-temperature impact) to ensure toughness performance in harsh environments.
From the production process point of view, both use the JCOE forming process (pre-bending → forming → expansion), but Q390GJC usually needs to add non-destructive testing links such as ultrasonic flaw detection (UT) and eddy current testing (ET) to ensure that the weld quality reaches the level II standard.

Second, the key performance comparison analysis of Q390GJB straight seam welded steel pipe
1. Welding performance: Q390GJB welded pipe uses H08Mn2SiA welding wire with CO₂ gas shielded welding, and the weld coefficient can reach above 0.9. Q390GJC has higher application requirements, so low-hydrogen electrodes (such as J507) are required. It needs to be preheated to 120-150℃ before welding to reduce the risk of cold cracks, and stress relief annealing at 600℃±15℃ is required after welding.
2. Weather resistance performance: Q390GJC often adds weather-resistant elements such as copper (0.20%-0.45%) and chromium (0.30%-0.60%). When used in coastal areas, its salt spray corrosion resistance is about 30% higher than that of Q390GJB. Experimental data show that in a C5-M level corrosion environment, the annual corrosion rate of Q390GJC is only 0.08mm/a.
3. Economic considerations: The current market quotation shows (June 2025) that the price per ton of Q390GJB straight seam welded pipe is about 4200-4500 yuan, while Q390GJC is 15%-20% higher due to its complex process. However, considering the life cycle cost, the use of Q390GJC in heavy-duty structures can reduce maintenance costs by more than 20%.

Third, typical application scenarios of Q390GJB straight seam welded steel pipes
1. Fluid transportation application of Q390GJB: In the branch pipeline network of the "West-East Gas Transmission" Line 3 project, Q390GJB welded pipes with a specification of Φ508×10mm are used, with a working pressure of 2.5MPa. X-ray detection is used to ensure that there are no unfused defects in the welds. Its inner wall adopts epoxy coal tar anti-corrosion coating with a design life of 30 years.
2. Structural engineering application of Q390GJC: The pier support system of the Hangzhou Bay Cross-sea Railway Bridge uses Φ800×25mm Q390GJC steel pipes, and its stability under a magnitude 8 earthquake condition is verified by finite element analysis. It is particularly noteworthy that the project requires the steel pipe ovality to be ≤0.5%D and the straightness deviation to be ≤1.5mm/m, reflecting the high-precision processing requirements.

Fourth, selection recommendations and quality control points for Q390GJB straight seam welded steel pipes
1. Selection decision tree
- When used for fluid transportation with a pressure of ≤1.6MPa and a limited budget, Q390GJB is preferred
- Q390GJC must be selected for dynamic loads (such as crane beams) or low-temperature environments (below -20°C)
- Q390GJC+hot-dip galvanizing composite treatment is recommended for corrosion environments above C4
2. Key items for quality control
- Raw material re-inspection: The carbon equivalent Ceq in the steel plant's warranty needs to be checked (Q390GJB requires ≤0.43%, Q390GJC ≤0.40%)
- Dimension tolerance: Pay special attention to the wall thickness deviation should be controlled within the range of +12.5%/-10%
- Weld detection: In addition to conventional radiographic detection, Q390GJC recommends adding TOFD (time difference diffraction) detection

Fifth, the industry development trend of Q390GJB straight seam welded steel pipe
With the implementation of the new NB/T 47013-2025 standard, Q390GJC steel pipes will develop in two directions in the future: one is to develop extra-thick wall steel pipes with a thickness of ≥40mm, using TMCP (thermomechanical control process) technology to ensure core toughness; the other is the popularization of intelligent production lines, through the laser vision system to achieve weld tracking accuracy of ±0.1mm, so that the product defect rate is reduced from the current 2% to below 0.5%.
It is worth noting that the rise of hydrogen energy pipelines has brought new opportunities for Q390GJB. Studies have shown that in 35MPa hydrogen pipelines, the use of Cr-Mo modified Q390GJB (adding 0.15% Mo) can effectively prevent hydrogen embrittlement, and this type of special welded pipe has begun to be tried in small-scale demonstration projects.

From the above analysis, it can be seen that the selection of the two types of steel pipes needs to comprehensively consider multiple dimensions such as mechanical properties, environmental factors, and cost control. In engineering practice, it is recommended to entrust a third-party testing agency (such as SGS, or BV) to conduct chemical composition spectrum analysis and mechanical property testing to ensure that the materials meet the design requirements. As steel structure buildings develop towards "higher, lighter, and stronger", the technical iteration of this type of high-performance welded pipe will continue to accelerate.