Longitudinally welded square and rectangular tubes are a type of welded shaped steel pipe. Produced from hot-rolled steel strip, they are first rolled into a round shape and joined via the high-frequency electric resistance welding (HFERW) process. They then undergo multi-pass roll forming to achieve their square or rectangular hollow cross-sections. Unlike tubes made by simply bending and welding flat plates, these feature a continuous, straight longitudinal weld seam. The seam undergoes professional treatment, and the tube body is straight and uniform. Suitable for both indoor and outdoor environments, they can be finished with hot-dip galvanizing or painting for corrosion protection, meeting the structural support and enclosure requirements of most standard engineering projects.
Utilizing high-frequency straight-seam welding technology, the weld is continuous and uniform with minimal defects and even stress distribution. Compared to simple bent-and-welded tubes, the weld is more stable; they are less prone to weld failure under moderate loads, ensuring greater overall safety.
We primarily supply straight-seam square and rectangular tubes from top brands like Youfa, Juncheng, Lida, and Huaqi, alongside cost-effective, value-priced options. With supplies across various tiers, we cater to both high-budget and cost-conscious projects, offering a wide range of purchasing choices.
Based in the Daqiuzhuang steel pipe hub, we maintain ready stock of mainstream specifications, eliminating long production wait times. Whether for standard sizes or small-to-medium batches of special specifications, we can quickly source and deliver materials to keep projects on schedule.
Compared to cold-drawn square and rectangular tubes, longitudinally welded square and rectangular tubes offer a clear price advantage. For moderate-load applications, there is no need to over-specify; these tubes meet engineering standards while effectively controlling total steel material costs.
The tubes are easy to cut, drill, weld, galvanize, and paint. They are resistant to sudden cracking during processing and yield a high-quality finished appearance, making them ideal for deep processing and fabrication requirements.
We handle everything from large-volume bulk orders for major projects to small-batch trial orders and material top-ups. There are no strict minimum order quantity (MOQ) thresholds; general contractors, processing plants, and small construction firms can all place orders.
| Parameter | What we supply |
| Product | Longitudinally welded square and rectangular tubes |
| Joint | A single longitudinal seam, high-frequency induction (ERW) welded through the full wall |
| Seam location | Centred on one flat face as standard; a corner or a nominated face if the drawing asks for it |
| Outside weld bead | Scarfed flush, held within roughly 0.2 mm of the face |
| Inside weld bead | As-welded by default; mechanically cleared when the bore has to stay open |
| Welding parameters | HF power, frequency and line speed, recorded every shift |
| Grades | Q235B, Q355B (supersedes Q345B), S235JR, S355JR, SS400, ASTM A500 Gr. A/B |
| Standards worked to | GB/T 13793-2016, GB/T 6728-2025, EN 10219-1/-2, ASTM A500, JIS G3466 |
| Square range | 20x20 mm up to 300x300 mm |
| Rectangular range | 20x40 mm up to 200x400 mm |
| Corner radius, outside | Around 2t on standard passes; 2t to 3t where the wall is heavy |
| Wall deviation | Held inside the tolerance of whichever standard the order is placed against; +/-10% is our working limit on basic grade, and +/-7.5% can be held on request |
| Length | 5.8 m, 6 m, 12 m, or cut to your list |
| Cut accuracy | About +/-1.5 mm, face square to the axis |
| Straightness limits | Bow within 2 mm per metre and within 0.15% of total length; twist free from visible defect |
| Finishes available | Black, oiled, pre-galvanized, hot-dip galvanized, powder coated |
| Weld verification | Flatten and bend test off the head of every coil; eddy current if you ask for it |
| Paperwork | Mill test certificate by heat number with chemistry and mechanicals, plus our dimensional and coating sheet |
| Bundling | Hexagonal bales under steel strap, wrapped in waterproof film; timber pallets added for ocean and rail |
Each longitudinally welded square and rectangular tubes comes with a quality certificate detailing the heat number, chemical composition, and mechanical properties. We also include our own inspection records for dimensions and coating thickness, as well as results from weld flattening and bending tests. Records are archived by heat number, allowing us to trace specific steel coils even if inquiries arise six months after delivery.
If a project requires third-party inspection, we arrange testing based on a standardized sampling plan and invite the inspection agency to witness production on-site. Please provide the relevant standards and inspection agency details when confirming the order so we can integrate this into our production schedule, rather than scrambling to arrange it at the last minute.
We prefer to hear about issues early rather than dealing with disputes later. Our hotline is staffed around the clock; we provide technical responses within 12 hours and propose solutions—such as replacement, supplementary supply, or compensation—within 48 hours. While we do not dispatch installation teams overseas, we can help you locate a local team and provide them with the necessary assembly drawings.
To get started, simply provide a cross-section list, a cutting list, and surface treatment specifications. For bolted connections, please submit connection drawings rather than just a hole location list; we will verify hole layouts, corner radii, and weld positions prior to material cutting.
We will provide pricing, the rolling schedule, and sample arrangements. Responses regarding cutting lists and processing drawings are typically provided within two days.
Free of charge; shipping costs are payable upon delivery (freight collect). Finalizing weld positions and coating specifications at this stage is the most cost-effective approach; delaying these decisions can lead to complications later.
Specifications and quantities can still be modified before production of the longitudinally welded square and rectangular tubes begins. Once production starts, we will notify you within 24 hours of any upstream changes (such as the arrival of steel coil stock).
Welding, sizing, and cutting; inspection based on sampling plans; packaging tailored to the actual mode of transport. Shipping documents accompany the goods.
A: Longitudinally welded square and rectangular tubes are not recommended for precision machined parts; cold-drawn square/rectangular tubes are preferred for precision machining. Straight-seam tubes are better suited for structural engineering applications.
A: The standard position is in the center of one of the flat sides. If drawings require it, the seam can be moved to the corner or to a specific face of your choice. If the tube requires cold bending, please inform us of the bending direction so we can position the weld seam away from the tension side.
A: Cracking does not occur during normal cutting operations; the integrity of the tube ends can be maintained by avoiding rapid high-temperature cutting and preventing sudden cooling after the cut.
A: In the "black pipe" (uncoated) state, the rust resistance of the weld seam is identical to that of the tube body. For long-term outdoor use, hot-dip galvanizing the entire tube is recommended to prevent the weld seam from rusting prematurely.
A: Using bare tubes directly in saline-alkali soil projects is not recommended. Due to the highly corrosive nature of such environments, hot-dip galvanizing is essential to extend the service life of the tubes.
How are the tubes transported? A: Shipment begins approximately 5 days after order confirmation, with subsequent deliveries made in batches. For sea and rail transport, dunnage (wooden supports) is placed beneath the bundles in addition to waterproof wrapping; for regional road delivery, steel-strapped bundles are used.
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S213 Jinghai District, Tianjin City, China
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