Description
Factory-direct seamless square and rectangular steel tube supply — Q235B and Q355B seamless hollow sections rolled, processed and documented under one roof, from billet to finished tube.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q355B Seamless Square and Rectangular Steel Tube |
| Product Type | Seamless Square and Rectangular Hollow Section |
| Steel Grade | Q195, Q215, Q235, Q345 (Q355), #20, #45; Equivalent: S195 / S235JR / S355JR / A53 Grade A / A53 Grade B / A500 Grade A / A500 Grade B / A500 Grade C / STK400 / SS400 / ST42.2 |
| Standard | EN10219 / EN10210 / GB/T 6728 / JIS G3466 / ASTM A500 / ASTM A36 / ASTM A53 |
| Section Shape | Square / Rectangular |
| Size Range | Square 20×20 mm – 500×500 mm; Rectangular 20×40 mm – 300×500 mm |
| Wall Thickness | 1.2 mm – 20 mm |
| Length | 3 m – 12 m (random or cut-to-length) |
| Technique | Seamless (Hot Rolled Hollow Carbon Pipe) |
| Surface Treatment | Hot Rolled / Pre-galvanized (Zn 40–80 g/m²) / Hot-dip galvanized (Zn 200–600 g/m²) / Customer’s requirement |
| Tolerance | ±1% |
| Ends | Plain (default) |
| Application | Construction & building structures / Steel structure engineering / Solar structure components / Machinery manufacturing / Shipbuilding / Power engineering / Greenhouse frames / Fence posts / Automobile chassis / Highway railings / Pressure vessels / Oil storage tanks / Bridges / Lifting and transportation machinery |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC & General Contracting | Building frames, column-beam assemblies, industrial platforms, equipment support structures |
| Steel Structure Fabrication | Trusses, portal frames, mezzanine floors, connection assemblies for warehouse and factory buildings |
| Solar & Renewable Energy | Solar panel support structures, mounting racks, inverter platforms |
| Infrastructure & Civil Works | Bridge railings, highway guardrail posts, lifting equipment frames, transportation machinery |
| Machinery & Industrial | Machinery frames, conveyor structures, crane booms, hydraulic cylinder sleeves |
| Agriculture & Enclosure | Greenhouse frames, fence posts, agricultural equipment chassis |
What Negative Tolerance Really Costs on a Seamless Square and Rectangular Steel Tube Order
A wall thickness that reads well on paper but fails caliper measurement at site will cost you far more than the price difference between a mill-direct tube and a trader’s offer.
Overseas buyers sourcing seamless square and rectangular steel tube from China often discover the gap between the mill test certificate and the actual product only after the container reaches the destination port. Wall thickness drifts below the specified tolerance, corners are out of square, and the heat number on the tube does not match the documentation. The result is not just a rejected shipment — it is rework on a structural frame that has already been partially erected, delayed handover to the main contractor, and a dispute over who bears the cost of replacement material. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements] For seamless tubes used in load-bearing frames and solar support structures, even a small deviation in wall thickness changes the section modulus and affects the structural calculation that the engineer signed off on.
How Seamless Process Matches Structural Frame and Solar Mounting Demands
Seamless square and rectangular steel tube produced by hot-rolling delivers more uniform corner integrity and mechanical consistency than welded alternatives, which matters when the tube will be drilled, welded and loaded in a structural frame. The absence of a longitudinal weld seam means the corner zones — where stress concentrates in moment-resisting connections — carry the same grain structure as the flat sides. For solar mounting systems exposed to coastal or industrial atmospheres, the hot-dip galvanized option (Zn 200–600 g/m²) provides long-term corrosion protection without field painting. Our own steel mill produces the raw hollow billets, so the chemical composition and rolling schedule are controlled from the first heat through to the finished tube — no third-party billet sourcing, no gap in material traceability.
Engineering Compliance and Certification Path for Overseas Projects
Structural engineers specifying seamless square and rectangular steel tube for EU projects require EN 10210 compliance with CE marking and factory production control documentation; North American projects typically call for ASTM A500 Grade B or C with mill test certificates conforming to EN 10204 3.1. The steel grade equivalence between EN (S235JR / S355JR), ASTM (A53 / A500) and GB (Q235B / Q355B) systems must be clearly documented so that the local inspector can verify conformity without requesting additional testing. [NEED_CITE: steel grade equivalence between EN 10210 and ASTM A500 standards] Cut-to-length capability within the 3–12 m range reduces on-site welding and secondary cutting, while the ±1% tolerance on wall thickness and section dimensions keeps fabrication sequencing on schedule. Third-party inspection by SGS, BV or TÜV before shipment provides the independent verification that EPC firms and general contractors require for project handover documentation.
Steel Grade Selection and Hot-Rolled Seamless Process Explained
The Q235B and Q355B grades cover the majority of structural and mechanical applications, with Q355B offering higher yield strength for heavier load-bearing frames and equipment supports. In international equivalence terms, Q235B corresponds to S235JR (EN) and A53 Grade B (ASTM), while Q355B maps to S355JR (EN) and A500 Grade B/C (ASTM) — a single product family that serves EN, ASTM, GB and JIS specification systems. [NEED_CITE: steel grade equivalence between EN and ASTM standards] The hot-rolled seamless process starts from a solid billet pierced and elongated into a hollow shell, then shaped into square or rectangular profile through a series of rolling passes — this produces a tube with no weld seam and consistent mechanical properties around the entire cross-section, including the corner radii. Surface treatment options range from hot-rolled black (for indoor or painted applications) through pre-galvanized (Zn 40–80 g/m², suitable for moderate exposure) to hot-dip galvanized (Zn 200–600 g/m², for aggressive outdoor or coastal environments). The wall thickness range of 1.2–20 mm covers everything from light greenhouse frames and fence posts to heavy industrial platforms and lifting equipment booms.
Hidden Costs of Sourcing the Wrong Grade or Unverified Tolerance
Ordering a tube that meets the drawing on paper but fails dimensional verification at site triggers a chain of costs: the local inspector rejects the material, the structural engineer must recalculate or redesign the connection, the erector stands idle waiting for replacement material, and the main contractor faces a liquidated damages claim from the project owner. [NEED_CITE: consequences of dimensional non-conformance in structural steel fabrication] Material without proper heat-number traceability cannot be accepted on EN 10210 or AISC-certified projects, regardless of whether the tube itself would perform adequately. A seamless square and rectangular steel tube supplier who cannot provide EN 10204 3.1/3.2 mill test certificates with full chemical composition and mechanical properties forces the buyer into costly third-party re-testing — or worse, acceptance of material that passes visual inspection but fails under load.
Why Buyers Choose Our Mill-Direct Supply Chain
We operate our own steel mill with three production lines and over 2,800 specifications in stock, so the seamless square and rectangular steel tube you order is rolled, processed and documented within a single facility — no trading company margin, no third-party billet uncertainty. Every heat is tested in our in-house laboratory, and the mill test certificate traces the chemical composition and mechanical results back to the original billet. Our fabrication division handles CNC cutting, drilling, welding and surface treatment to engineering drawings, so you can source the raw tube and the fabricated component from one point of accountability. We hold CE certification per EN 10210 and EN 10219, ISO 9001 quality management, and we regularly arrange SGS, BV and TÜV third-party inspections for EU, Middle East and Southeast Asian projects. Non-standard sizes, cut-to-length requirements and custom surface treatments are handled against the same quality system — the same caliper check, the same heat-number traceability, the same documentation package.
Documentation & Compliance
- Mill test certificate documenting Q235B / Q355B chemical composition and mechanical properties per EN 10210 / ASTM A500, with full heat-number traceability from billet to finished tube
- CE certificate confirming factory production control compliance with EN 10210 and EN 10219 for seamless hollow sections destined for EU structural projects
- ISO 9001 quality management certificate covering the integrated steel mill and fabrication workshop
- SGS / BV / TÜV third-party inspection report verifying wall thickness, section dimensions, surface coating weight and visual quality before shipment
- Material traceability by heat number stamped on each tube, cross-referenced to the mill test certificate and packing list
- Full customs documentation package including packing list, bill of lading, certificate of origin and commercial invoice formatted for the destination country
Packaging, Loading & Delivery
- Seamless square and rectangular steel tube bundled with high-tensile steel strips and edge protectors to prevent surface damage and preserve the galvanized coating during ocean transit
- Hot-dip galvanized tubes wrapped with waterproof paper and plastic sheeting at the bundle level to prevent white rust formation during humid container shipping
- Cut-to-length tubes (3–12 m) loaded with optimized container stowage plans to maximize payload per 20ft or 40ft container, reducing per-ton freight cost for project buyers
- Heat number and steel grade stenciled on each tube end for on-site identification and traceability verification by the receiving inspector
- FOB, CFR, CIF and DDP terms available with professional oversized cargo loading and lashing for heavy-wall Q355B sections and long-length bundles
- Door-to-door logistics coordination including export customs clearance at origin port and delivery tracking until site arrival
How to Request a Quotation with Full Mill Documentation
Send your project drawings (PDF or DWG), specify the steel grade (Q235B / Q355B or international equivalent), section dimensions, wall thickness, length, surface treatment and required standard — we respond within 24 hours with a detailed quotation including material, fabrication, coating, packing and shipping costs, together with the shop drawing timeline and production schedule. If your project requires CE certification, third-party inspection or specific mill test certificate format, confirm this at the inquiry stage so the documentation package is prepared in parallel with production.
Start Your Seamless Square and Rectangular Steel Tube Inquiry
Submit your specifications, steel grade and destination port to receive a quotation with mill test certificate and compliance documentation.
Company: Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.xjystructure.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@xjystructure.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
