Q235 Carbon Steel Pipe Factory Direct: Large Diameter Carbon Steel Pipe Price and Welding Process Details

I. Material Properties and Industrial Applications of Q235 Carbon Steel Pipe
Q235 carbon steel pipe is one of the most commonly used structural steel materials in my country's industrial sector. Its excellent comprehensive properties have earned it a crucial position in construction, machinery manufacturing, and pipeline engineering. The "Q" in the steel's name stands for yield strength, and "235" refers to its lower yield strength limit of 235 MPa. This naming scheme intuitively reflects the material's fundamental mechanical properties. Chemically, Q235 steel contains a carbon content between 0.05% and 0.70%, along with alloying elements such as silicon and manganese. This composition ensures sufficient strength while maintaining excellent ductility and toughness.

Q235 steel's most notable characteristic is its excellent weldability, primarily due to its low carbon content and optimal alloying ratio. During welding, Q235 steel is less susceptible to hardened microstructures and exhibits a low tendency to cold cracking in the weld joint area, making it particularly suitable for steel structure projects requiring extensive welding. Q235 steel is divided into four grades, A, B, C, and D, depending on the impact temperature. Q235D grade steel maintains excellent impact toughness even at temperatures as low as -20°C, giving it a distinct advantage in engineering applications in cold regions.

In terms of mechanical properties, Q235 steel boasts a tensile strength of 375-460 MPa and a standard elongation of 26%. These characteristics enable it to withstand significant deformation without breaking, a characteristic particularly important during pipeline installation and structural assembly.

From an economic perspective, Q235 steel's relatively simple smelting process and low production costs give it a competitive advantage in price-sensitive projects. It's worth noting that while Q235 steel isn't specifically designed for pressure vessels, it's still used in pressure vessel manufacturing in non-high-pressure applications due to its extensive experience and widespread availability.

In practice, Q235 carbon steel pipes are often used in industrial components such as tie rods and hooks, and their production accounts for a significant proportion of total steel production, reflecting their importance in the industrial sector.

II. Large-Diameter Carbon Steel Pipe Market Price Trends and Procurement Strategies
In 2025, the large-diameter carbon steel pipe market showed a clear price stratification, with the mainstream price range ranging from 3,400 to 9,070 yuan/ton. This price difference is primarily due to differences in material, specifications, and processing precision.
Take Q235B as an example. Its market price is approximately 3,600-4,000 yuan/ton, making it an economical choice for building structures and mechanical frameworks. However, it should be noted that its relatively low strength may cause deformation under heavy loads.
In contrast, 15CrMoG alloy pipes are priced as high as 8,970-9,070 yuan/ton. Although costly, their excellent high-temperature resistance makes them an essential material for special applications such as power plant boilers.

Specifications also have a significant impact on price. The combination of outer diameter and wall thickness directly determines material usage and processing difficulty. For example, a 60mm outer diameter, 4mm wall thickness carbon steel pipe costs approximately 161 yuan per pipe, while a 100mm outer diameter, 5mm wall thickness pipe costs 55.7 yuan per meter.

Increasing wall thickness significantly increases material costs. In one case, using 8mm wall thickness pipe increased material costs by approximately 23%.

In terms of processing precision, the price range for ordinary seamless 45 steel pipe is 4,500-5,200 yuan per ton, while cold-drawn precision steel pipe can reach 4.28 yuan per meter. While this represents an 18% cost increase, the superior interior finish reduces long-term maintenance costs.

The latest market data from September 2025 shows that the price of carbon structural steel fluctuates between 3,600 and 4,837 yuan per ton. Specifically for large-diameter specifications, the price of 325×8mm Q235B carbon steel pipe is approximately 4,350-4,450 yuan/ton, while the price of 529×10mm thick-walled pipe reaches 4,800-4,900 yuan/ton.

Market trends indicate that a slowdown in energy project procurement has led to a decline in the transaction price of large-diameter carbon steel pipe, with a weekly drop of 30-50 yuan/ton.

In terms of procurement strategy, bulk purchases generally offer more favorable prices, with some manufacturers stating that "negotiable for larger quantities," providing room for cost optimization for large-scale projects.

III. Key Technologies for Welding Processes for Large-Diameter Carbon Steel Pipes

The welding quality of large-diameter Q235 carbon steel pipes directly impacts the safety and service life of the pipeline system, so strict control must be exercised throughout the entire welding process. Taking 820mm×10mm spiral welded pipe as an example, the typical welding process includes four key stages: pre-weld preparation, root weld, filler weld, and cap weld.

During the pre-welding preparation phase, a ZX7-400 AC arc welder and E4303 electrodes should be used. The electrodes should be dried at 150°C for one hour. Oil, rust, and other impurities should be thoroughly cleaned within a 60mm radius on both sides of the groove until the metallic luster is revealed.

When assembling the pipes, ensure concentricity between the pipes, and limit misalignment to within 1.5mm. This requires the use of 8-10 positioning plates evenly spaced around the pipes for securing.

The root pass weld is a critical step in ensuring weld quality. A 3.2mm diameter electrode should be used, with a current of 115-125A, for single-sided welding and double-sided forming.

During welding, the principle of "center arc start, right arc extinguish" should be strictly adhered to. This means that after striking the arc at the center of the groove gap, the electrode should be quickly swung horizontally to the left side of the groove, then back to the right side and downward to extinguish the arc. Each cycle should take approximately 1.5 seconds. The welding position should be adjusted to the optimal operating range of 8:30 to 10:30 (4:30 to 2:30) by rotating the pipe fitting. Positioning plates should be removed one by one as the weld extends.

For the filler weld, a 3.2mm diameter electrode should still be used, with the current increased to 115-130A and an "8" motion. This technique ensures a smooth filler weld and avoids deep grooves and interlayer slag inclusions.

For the cap weld, a 4mm diameter electrode should be used and the current adjusted to 150-160A.

During welding, special attention should be paid to controlling the interpass temperature; if the temperature does not meet the requirements, reheat the weld.

For overhead welding of large-diameter pipes, a low-speed welding method should be used to prevent overflow of the molten pool.

Post-weld treatment is equally important. The weld should be subjected to slow cooling. Typically, a composite slow cooling device consisting of an asbestos blanket and felt is used to wrap the weld joint for at least half an hour. Under special environmental conditions, such as low-temperature regions in northern China, the material's low-temperature toughness must also be considered, and appropriate welding materials and process parameters must be selected.

IV. Advantages and Implementation Key Points of the Factory Direct Supply Model
The factory direct supply model is becoming increasingly popular in the procurement of large-diameter carbon steel pipes. By eliminating intermediaries, this model significantly reduces procurement costs. For example, Sichuan Luxintong Metal Products Co., Ltd. offers spot sales of 20# seamless pipes with a clear "factory direct supply, negotiable for large quantities" label, providing price negotiation for bulk purchasers.

Hebei Hongxincheng Pipeline Co., Ltd. provides a direct supply service for steel-jacketed steam-insulated steel pipes for heating needs. This specialized production model ensures a precise fit between the product and specific application scenarios.

The advantages of the direct supply model lie not only in price but, more importantly, in its ability to provide customized production. Langfang Aoyang Insulation Materials Co., Ltd. offers prefabricated direct-buried insulated steel pipes, which can be treated with polyurethane foam insulation to meet the specific needs of municipal heating pipes. This flexibility is difficult to achieve through traditional distribution channels. Tianjin Mingcheng Steel Sales Co., Ltd. demonstrated more sophisticated processing capabilities, offering value-added services including sawing and beveling, which significantly reduce on-site processing workload for construction companies.

When implementing factory direct supply, several key points should be considered: First, verify the manufacturer's qualifications and production capacity to ensure a stable supply of standard products; second, clarify quality standards and acceptance criteria, especially for pipes with special specifications or high performance requirements; and finally, evaluate logistics and distribution capabilities, as transporting large-diameter carbon steel pipe requires specialized equipment and solutions.
For international trade needs, specialized manufacturers, such as those providing ASTM steel pipe, can also produce according to international standards to meet the specific requirements of overseas projects.