Q235B straight seam welded steel pipe is a widely used pipe in the fields of construction, machinery manufacturing, steel structure, etc. Its performance characteristics, production process, and market application have always been the focus of attention in the industrial field.

First, analysis of Q235B material characteristics
Q235B is a carbon structural steel, which is a common grade in China’s GB/T700 standard. Its chemical composition is carbon (C) ≤ 0.20%, silicon (Si) ≤ 0.35%, manganese (Mn) ≤ 0.35%-0.80%, and phosphorus (P) and sulfur (S) content are controlled below 0.045%. The letter “B” indicates the quality grade, which is different from grade A (no impact requirement) and grade C (higher low-temperature toughness). Q235B has an impact energy requirement of ≥ 27J at a room temperature of 20℃, which is more suitable for environments with dynamic loads. In terms of mechanical properties, the yield strength of Q235B is ≥235MPa, the tensile strength is 375-500MPa, and the elongation is ≥26%. This moderate strength combined with good plasticity makes it an ideal base material for welded steel pipe manufacturing. It is worth noting that Q235B has excellent welding performance, and the carbon equivalent (Ceq) is usually controlled below 0.3%. No complex preheating process is required during welding, which greatly reduces the processing cost.

Second, the production process of Q235B straight seam welded steel pipe
The production of straight seam welded steel pipe (LSAW) mainly adopts high-frequency resistance welding (ERW) or submerged arc welding (SAW) process. Taking the processing flow of a supplier as an example, a typical production line includes the following links:
1. Uncoiling and leveling: Unroll and level the Q235B hot-rolled coil to eliminate curling stress
2. Milling edge processing: Use a double milling machine to precisely process the edge of the strip to ensure the smoothness of the welding surface
3. Forming welding: Form into a tube through multiple roll bending, and use high-frequency induction welding (frequency 100-400kHz) to achieve instant fusion
4. Online heat treatment: The weld is annealed by medium-frequency induction to eliminate welding residual stress
5. Sizing and straightening: The hydraulic straightening machine ensures that the straightness deviation is ≤1mm/m
6. Water pressure test: The standard requires a 6MPa holding time of ≥5 seconds
Compared with spiral welded steel pipes, straight seam welded steel pipes have the characteristics of high dimensional accuracy (diameter tolerance ±0.5mm) and small ovality (≤0.6%D), which is particularly suitable for occasions requiring precision assembly. The advanced production line using JCOE forming technology can control the wall thickness uniformity within ±5%.

Third, application scenarios and engineering cases of Q235B straight seam welded steel pipes
Q235B straight seam welded steel pipes are mainly used in three major fields:
1. Building structure: A commercial complex project uses Φ219×6mm welded steel pipes as the curtain wall support system, with a single load-bearing capacity of 8 tons. Its advantage is that the node connection is convenient, and it can be connected to the steel plate by direct welding, eliminating the flange assembly.
2. Fluid transportation: In low-pressure (≤1.6MPa) water-gas pipelines, DN150 welded steel pipes replace traditional cast iron pipes, reducing weight by 40% and improving corrosion resistance. It should be noted that the working temperature should be maintained in the range of -20℃ to 300℃.
3. Machinery manufacturing: A construction machinery company uses 80×40mm rectangular welded steel pipes to make forklift gantry frames, and the local yield strength is increased to 345MPa through the cold bending strengthening process.
Special application cases show that the service life of galvanized Q235B welded steel pipes in transmission towers in coastal areas can reach 25 years. When the zinc layer adhesion is ≥610g/m², the salt spray test is more than 1000 hours without red rust.

Fourth, the market status and price trend of Q235B straight seam welded steel pipes
The latest quotation shows that the wholesale price of Q235B straight seam welded steel pipes with a specification of Φ48×3.5mm in April 2025 is 3850-4200 yuan/ton, up 1.2% from the previous month. The current market presents three characteristics:
1. Regional differentiation: the inventory turnover cycle in East China is shortened to 12 days, while the delivery time in North China is extended to 20 days due to environmental protection production restrictions
2. Specification premium: the price difference between thin-walled (δ≤3mm) products and thick-walled products has widened to 300 yuan/ton
3. Alternative competition: the market share of Q355B welded steel pipes has increased by 5% year-on-year, but Q235B still maintains a 75% cost advantage in conventional uses
It is worth noting that the “fixed-length intelligent cutting” service launched by a supplier can cut 6-meter standard pipes on demand, increasing material utilization from 85% to 98%, which is particularly suitable for small engineering projects.

Fifth, the key points of purchasing and quality control of Q235B straight seam welded steel pipes
Combined with the suggestions of multiple industry sources, the following should be paid attention to when purchasing Q235B straight seam welded steel pipes:
1. Qualification documents: Suppliers are required to provide CMA-certified mechanical properties test reports, and special attention should be paid to the measured yield strength value, which should not be less than 245MPa
2. Appearance inspection: The weld excess height should be ≤2.5mm, and there should be no “bite edge” defects; when spot-checked with an eddy current flaw detector, the defect signal should not exceed 50% of the artificial defects of the standard sample pipe
3. Usage suggestions:
- When used under pressure, the recommended working pressure is ≤1.6MPa
- In low temperature environments (<-20℃), Q235D material should be considered
- Plasma cutting is recommended for cutting to avoid local hardening caused by carbon arc gouging
A failure analysis case shows that the illegal use of Q235B welded steel pipes to make pressure vessel supports (design stress up to 310MPa) led to early fractures. This reminds us that we must strictly follow the applicable scope of GB/T 13793-2016. As steel structure buildings develop towards “assembly”, Q235B straight seam welded steel pipes are upgrading towards high precision and lightweight. Some leading companies have begun to provide value-added services such as pre-punching and end threading, giving this type of traditional material new market vitality.