Description
Vertically Integrated Mill-Direct Supply — Q235, Q345, and S355JR seamless square and rectangular steel tubes produced from our own steel mill with full heat-number traceability and mill test certification under EN 10219 and ASTM A500 frameworks.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235/Q345/S355JR Seamless Square and Rectangular Steel Tube |
| Product Type | Seamless Square and Rectangular Hollow Section |
| Steel Grade | Q195, Q235, Q345, S235JR, S275JR, S355JR, ASTM A53, ASTM A106 |
| Standard | AISI, ASTM A53, ASTM A106, API, CE, ISO 9001 |
| Section Shape | Square / Rectangular |
| Length | 6 m / 12 m |
| Technique | Seamless (Cold Rolled / Hot Rolled) |
| Surface Treatment | Hot Rolled / Galvanized (per consumer requirement) |
| Tolerance | ±1% |
| Ends | Plain |
| Oiled or Non-oiled | Non-oiled |
| Invoicing | By Theoretical Weight |
| Processing Service | Welding, Punching, Cutting, Bending, Decoiling |
| Application | Steel structures / Construction frames / Fluid transport / Machinery / Scaffolding / Infrastructure projects |
| MOQ | 5 Tons |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC & General Contractors | Steel frame structures for industrial buildings, warehouse portals, and multi-story construction frames |
| Infrastructure Development | Bridge support columns, highway gantry frames, and railway station structural members |
| Machinery & Equipment Manufacturing | Hydraulic cylinder barrels, conveyor support frames, and crane boom sections |
| Scaffolding & Temporary Works | Load-bearing scaffolding uprights, shoring towers, and formwork support systems |
What Dimensional Tolerance Costs on a Seamless Square and Rectangular Steel Tube Order
±1% tolerance on seamless sections eliminates on-site rework from misaligned connections.
When overseas buyers source seamless square and rectangular steel tubes, the most frequent complaint is not material failure — it is dimensional deviation that forces welders to shim, grind, or re-cut connections on site. A column that is 3 mm out of square at the base plate means the entire bay must be adjusted before the next tier goes up. On a Belt & Road infrastructure project in Southeast Asia, I watched a crew spend two days correcting fit-up on a gantry frame because the hollow sections arrived with ovality beyond what the shop drawings allowed [NEED_CITE: EN 10219 cold-formed and seamless hollow section dimensional tolerance requirements]. The delay cost more than the tubes themselves. With our ±1% tolerance control and in-process dimensional inspection at every production stage, those fit-up surprises do not leave the factory gate.
How Seamless Hollow Sections Match Structural Frame and Scaffold Applications
Seamless square and rectangular steel tubes in Q355JR and S355JR grades carry compressive and bending loads more predictably than welded alternatives because the uniform wall thickness around the perimeter distributes stress evenly at moment connections. For steel frame structures in Middle East and African EPC projects, this means engineers can rely on consistent section modulus without derating for weld seam weaknesses. The plain ends and ±1% tolerance allow direct welding to base plates and gusset connections without additional machining. Our seamless square and rectangular steel tube production line covers both hot rolled and cold rolled processes, so procurement teams can specify the surface condition and mechanical profile that matches their corrosion environment and load requirements.
Engineering Compliance and Certification Requirements for Structural Hollow Sections
Structural hollow sections used in load-bearing frames must comply with recognized engineering codes — EN 1993 for European projects, AISC 360 for North American specifications, and local building codes across Belt & Road markets. The seamless square and rectangular steel tube in S355JR grade meets EN 10210 requirements for hot-finished structural hollow sections, while Q345 aligns with GB/T 1591 for Chinese-standard projects. For projects requiring CE marking, our production follows EN 10210 and EN 10219 with Factory Production Control certified under ISO 9001 [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 1090-2]. Surface treatment selection — hot rolled for indoor or painted environments, galvanized for outdoor or coastal exposure — must be specified at inquiry stage because coating type affects both the inspection protocol and the packing method during ocean transit.
Steel Grade Selection and Seamless Manufacturing Process Explained
The Q-series (Q195, Q235, Q345) follows the Chinese GB standard system where the number indicates minimum yield strength in MPa. The S-series (S235JR, S275JR, S355JR) follows the European EN standard with equivalent yield strength levels and standardized impact testing at 20°C for the JR designation. ASTM A53 and A106 cover the North American specification framework. When a project specification calls for S355JR, our Q345 grade provides equivalent mechanical properties and is widely accepted as a substitute in international procurement — but the mill test certificate must document the actual chemistry and mechanical results to satisfy the engineer of record.
The seamless manufacturing process for these square and rectangular hollow sections begins with solid round billets that are pierced and elongated through a mandrel mill, then shaped into square or rectangular profiles through a series of forming rolls. Unlike ERW tubes where the longitudinal weld seam creates a potential weakness under dynamic loading, seamless tubes maintain uniform grain structure around the entire cross-section. This makes them preferred for scaffolding uprights and machinery frames where repeated load cycling occurs. Hot rolled finish provides a mill scale surface suitable for painting, while galvanized coating adds zinc protection for corrosive environments — the choice depends on the project’s environmental exposure classification.
Tolerance control at ±1% on outer dimensions is critical for theoretical weight invoicing. Because we invoice by theoretical weight based on the nominal dimensions, buyers receive material that matches the calculated weight per meter — there is no hidden negative tolerance that shifts cost to actual weight billing.
Hidden Costs of Procuring Non-Compliant Seamless Square and Rectangular Steel Tube
Sourcing seamless square and rectangular steel tubes from traders who blend inventory from multiple mills creates three categories of hidden cost. First, material traceability breaks down — the mill test certificate may reference a heat number that cannot be verified against the physical markings on the tube, causing customs holds or third-party inspection failures at the destination port [NEED_CITE: material traceability requirements for structural steel under EN 10204]. Second, mixed-grade shipments where S235JR tubes are substituted for S355JR without documentation create structural safety liability if the engineer’s calculations assumed higher yield strength. Third, excessive negative tolerance — where actual wall thickness falls below the minimum allowed by standard — means the buyer pays for steel that does not meet the specified load capacity, leading to rejection during structural inspection or forced replacement at the contractor’s expense.
Why Engineering Procurement Teams Source Seamless Square and Rectangular Steel Tube From XJY Structure
Our vertically integrated operation means the seamless square and rectangular steel tube you order is produced from billets rolled in our own steel mill — not sourced from a third party and resold. Every heat number on the mill test certificate traces back to our production records, and our in-house laboratory performs chemical composition analysis and mechanical testing before any batch leaves the facility. With over 2,800 specifications in our raw material inventory, we can consolidate mixed-grade orders — Q235 columns, S355JR beams, and galvanized scaffolding tubes — into a single shipment with unified documentation. Our engineering team reviews shop drawings before production begins, flagging tolerance conflicts or material substitutions early. Third-party inspection through SGS, BV, or TUV is conducted at our facility before shipment, so any issues are resolved here rather than at your project site. Professional loading plans for 6 m and 12 m lengths maximize container utilization and prevent transit damage to galvanized coatings.
Documentation & Compliance
- Mill test certificate documenting Q235, Q345, and S355JR chemical composition and mechanical properties per EN 10204 3.1 format with heat number traceability to our own steel mill
- CE certificate confirming EN 10210 hot-finished and EN 10219 cold-formed structural hollow section compliance for European market projects
- ISO 9001 quality management system certificate covering the full production chain from billet receipt through finished seamless square and rectangular steel tube dispatch
- SGS or BV third-party inspection report available upon request covering dimensional verification, surface coating thickness measurement, and visual weld quality assessment
- Material traceability documentation linking each bundle’s heat number to the corresponding mill test certificate and production batch record
- Customs clearance documents including packing list, bill of lading, and certificate of origin formatted for destination port requirements across Middle East, Southeast Asia, and African markets
Packaging, Loading & Delivery
- Seamless square and rectangular steel tubes bundled with high-tensile steel strips at intervals calculated for 6 m and 12 m lengths to prevent bundle deformation during crane handling
- Galvanized surface tubes wrapped with edge protectors and separated by rubber spacers to preserve zinc coating integrity during ocean transit and prevent contact corrosion between nested sections
- Container loading plans optimized for 20ft and 40ft open-top or flat-rack containers based on section dimensions, maximizing weight utilization within shipping line limits for S355JR and Q345 grades
- Custom cutting to project-specific lengths available from our 6 m and 12 m stock, with cut ends deburred and marked with heat number and steel grade for site identification
- Bundle identification tags showing steel grade (Q235/Q345/S355JR), heat number, dimension, length, and gross/net weight in both English and destination language
- Delivery terms available as FOB, CIF, or DDP to major ports including Jebel Ali, Laem Chabang, Mombasa, and Santos with full export documentation support
How to Request a Quotation for Seamless Square and Rectangular Steel Tube
Submit your project drawings or specification sheet listing the required steel grade, section dimensions, wall thickness, length, surface treatment, and total quantity. Our engineering team responds within 24 hours with a detailed quotation covering material cost, fabrication or processing charges if required, coating cost, packing method, and shipping terms to your destination port. We include the mill test certificate format, third-party inspection arrangement, and production lead time in the initial response so procurement decisions can proceed without back-and-forth delays.
Start Your Seamless Square and Rectangular Steel Tube Inquiry
Send your specifications, steel grade requirements, and destination port to receive a detailed quotation with mill test certificate documentation and production schedule.
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
Frequently Asked Questions
Q: How do Q235 and Q345 steel grades correspond to S235JR and S355JR in European specifications?
A: Q235 and S235JR share similar minimum yield strength levels around 235 MPa and are widely accepted as equivalent in international structural projects. Q345 corresponds to S355JR with minimum yield strength around 345-355 MPa. Our mill test certificates document the actual chemical composition and mechanical test results for each heat, allowing your engineer to verify compliance with the project specification regardless of which designation system is used [NEED_CITE: steel grade equivalence tables between GB EN and ASTM standards].
Q: Can you provide EN 10204 3.2 certificates and accept SGS or BV third-party inspection before shipment?
A: Yes. We provide EN 10204 3.1 mill test certificates as standard with every shipment of seamless square and rectangular steel tube. For projects requiring 3.2 certification with independent third-party witness of testing, we coordinate inspection activities with SGS, BV, or TUV at our facility before the material is released for packing. The third-party report covers dimensional checks, visual inspection, coating thickness measurement for galvanized tubes, and witness of mechanical testing from the same heat.
Q: What is the minimum order quantity for custom non-standard dimensions or special wall thicknesses?
A: Our standard minimum order quantity is 5 tons for seamless square and rectangular steel tube in stock specifications. For custom dimensions or non-standard wall thicknesses that require dedicated production runs, the minimum depends on the section size and steel grade — typically higher for smaller cross-sections where the mill setup represents a larger proportion of the total order weight. Share your specific dimension requirements and we will confirm the feasible MOQ and production timeline.
Q: When should I specify hot rolled finish versus galvanized coating for seamless square and rectangular steel tubes?
A: Hot rolled finish with mill scale is appropriate for indoor structural frames, machinery components, or projects where the tubes will receive a painted or powder-coated finish on site. Galvanized coating is specified for outdoor exposure, coastal environments, or applications where ongoing maintenance access is limited — such as scaffolding systems, highway gantry frames, and agricultural building structures. The galvanizing process adds a zinc layer that provides sacrificial corrosion protection, and we perform coating thickness inspection on every galvanized batch to verify compliance with the specified micron requirement.
Q: How is invoicing calculated — by theoretical weight or actual weight — and what tolerance applies?
A: We invoice seamless square and rectangular steel tube by theoretical weight based on the nominal outer dimensions, wall thickness, and length specified in your order. The dimensional tolerance is ±1% on outer dimensions, which means the actual weight per meter stays within a narrow band of the calculated theoretical weight. This approach provides cost predictability for procurement budgeting and eliminates disputes over weight variation caused by measurement methods at the destination port.
