Q235 welded pipe is a steel pipe made of Q235 steel strip or steel plate, which is welded after curling. Because of the high-frequency welding technology used in its production process, it is also called high-frequency welded pipe. As a representative product of carbon structural steel welded steel pipe, Q235 welded pipe has become one of the preferred pipes in the construction, machinery, transportation, and other industries due to its excellent mechanical properties, economical price, and wide application fields. Among them, Q235 straight seam welded pipe, as an important branch of welded pipe, occupies an important position in low-pressure fluid transportation, structural support, and other fields with its unique longitudinal weld structure and stable quality performance.
First, the material characteristics and standard specifications of Q235 straight seam welded pipe
Q235 steel is an ordinary carbon structural steel with a yield strength of 235MPa and excellent plasticity and welding properties. According to the national standard GB/T 3091-2015 “Welded Steel Pipe for Low-Pressure Fluid Transportation”, Q235 welded pipes must meet the following technical requirements:
1. Chemical composition: carbon content ≤0.22%, manganese content ≤1.4%, sulfur, phosphorus, and other impurities are strictly controlled to ensure welding quality and corrosion resistance.
2. Mechanical properties: tensile strength 375-500MPa, elongation ≥20%, able to withstand certain impact and bending deformation.
3. Process standards: straight seam welded pipes adopt JCOE (pre-bending, forming, welding, expanding) process, and the welds must be tested by ultrasonic or X-ray to ensure that there are no defects such as infusion and pores.
Second, the production process and technical points of Q235 straight seam welded pipes
The production process of Q235 straight seam welded pipes mainly includes uncoiling, leveling, shearing, forming, welding, cooling, sizing, cutting, and other links. Among them, high-frequency welding (HFW) is the core process:
- High-frequency current welding: Utilize the skin effect and proximity effect of high-frequency current to instantly heat the edge of the steel strip to a molten state, and achieve metallurgical bonding under the action of the extrusion roller. This technology has high efficiency and low energy consumption, and the weld strength can reach more than 90% of the parent material.
- Weld treatment: After welding, internal and external burrs need to be removed, and residual stress is eliminated through online heat treatment to improve weld toughness. Some high-end products will also undergo water pressure testing or eddy current testing to ensure sealing.
Third, the classification and specification parameters of Q235 straight seam welded pipes
According to the purpose and processing method, Q235 welded pipes can be divided into the following categories:
1. According to the weld form:
- Straight seam welded pipe: The weld is parallel to the axis of the steel pipe, suitable for pipes with a diameter of ≤406mm, with common specifications of Φ20-Φ426mm and a wall thickness of 1.0-20mm.
- Spiral welded pipe: The weld is spiral, suitable for large-diameter (Φ219-Φ3000mm) pipelines, but the compressive strength is slightly lower than that of straight seam pipes.
2. By surface treatment:
- Galvanized welded pipe: The hot-dip galvanized layer can improve corrosion resistance and is widely used in outdoor guardrails, scaffolding, etc.
- Black pipe (non-galvanized): Lower cost, mostly used for structural support or after painting.
Fourth, application scenarios and advantages of Q235 straight seam welded pipe
1. Construction engineering: As scaffolding and steel structure support columns, Q235 straight seam welded pipe can reduce the construction load cost with its high strength and lightweight characteristics. 2. Fluid transportation: used for low-pressure pipelines such as tap water and gas, its sealing and pressure resistance fully meet the requirements of GB/T 3091 standard.
3. Machinery manufacturing: Q235 welded pipes are often used for parts such as agricultural machinery frames and automobile transmission shafts. During processing, they can be processed through secondary forming such as cold bending and punching to meet different needs.
Fifth, the market status and development trend of Q235 straight seam welded pipes
In 2025, with the continuous increase in domestic infrastructure investment, the annual demand for Q235 welded pipes is expected to exceed 30 million tons. The market competition presents the following characteristics:
- Green production: Steel mills gradually promote high-frequency welding waste heat recovery technology to reduce energy consumption by more than 30%.
- High-end transformation: Some companies develop Q235B-grade welded pipes (adding trace alloy elements) for oil and gas pipelines resistant to low-temperature environments (-20°C).
- Intelligent detection: AI visual recognition system is introduced into the weld quality inspection link, and the defect detection rate is increased to 99.5%.
Sixth, Q235 straight seam welded pipe selection and use recommendations
1. Quality identification: Check whether the surface of the steel pipe is smooth and crack-free and whether the weld is flat; require suppliers to provide third-party test reports (such as SGS certification).
2. Anti-corrosion measures: Hot-dip galvanizing or epoxy resin coating is recommended for outdoor use, and rust should be checked regularly in humid environments.
3. Cutting precautions: Avoid flame cutting. Grinding wheel saw or plasma cutting is recommended to prevent the weld area from being affected by heat and causing performance degradation.
As a basic industrial material, the Q235 welded pipe is difficult to replace in the short term due to its technical maturity and cost-effectiveness. In the future, with the integration of new materials and new processes, its application boundaries will be further expanded to emerging fields such as new energy equipment and intelligent warehousing.
Post time: Jun-16-2025