Description
Factory-Direct Square & Rectangular Steel Tubes — XJY Structure controls the full chain from raw billet to finished Q235B Q355B square rectangular steel tube, eliminating third-party sourcing gaps that cause material traceability failures.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B/Q355B Square and Rectangular Carbon Steel Tube |
| Product Type | Square / Rectangular Steel Tube (Hollow Section, RHS/SHS) |
| Steel Grade | Q195, Q235, Q355, S235JR, S355JR, A53 Grade A, A53 Grade B, A500 Grade A, A500 Grade B, A500 Grade C, SS400, STK400, ST42.2, S195 |
| Standard | EN10219, EN10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A36, ASTM A53 |
| Section Shape | Square / Rectangular |
| Size Range | Square: 20×20mm–500×500mm; Rectangular: 20×40mm–300×500mm |
| Wall Thickness | 1.2mm–20mm |
| Length | 3m–12m (random or cut-to-length) |
| Technique | Hot Rolled / ERW (Welded Hollow Section) |
| Surface Treatment | Pre-galvanized (40–80g/m²), Hot-dipped galvanized (200–600g/m²), Hot Rolled (Black) |
| Tolerance | ±1% |
| Material | Low carbon steel |
| Ends | Plain |
| Application | Construction / Structural steel frames / Solar structures / Fence posts / Greenhouse frames / Machinery / Shipbuilding |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC & Industrial Construction | Factory warehouse frames, platform supports, pipe rack structures, mezzanine beams |
| Infrastructure & Renewable Energy | Solar panel mounting structures, highway fencing posts, greenhouse skeleton frames |
| General Building & Civil Works | Column sections, bracing members, stairway handrails, door and window frames |
| Machinery & Shipbuilding | Conveyor frame assemblies, equipment base structures, ship interior support members |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A 0.3mm negative tolerance deviation can trigger full-container rejection at third-party inspection.
When overseas buyers source Q235B Q355B square rectangular steel tube from fragmented traders, the material passes through multiple hands before reaching the fabrication floor. Each intermediary layer weakens the traceability chain — heat numbers get mixed, mill test certificates get delayed, and wall thickness tolerances drift toward the negative limit. I have seen entire shipments held at destination ports because the实测 wall thickness fell below the minimum allowed by EN10219, even though the paperwork looked correct at origin. The real cost is not the rejected steel; it is the crane idle time, the rescheduled welding crews, and the air-freight replacement that follows. [NEED_CITE: EN 10219 cold-formed structural hollow section tolerance requirements]
Matching Hollow Section Profiles to Structural Load Paths
Square and rectangular hollow sections distribute load evenly across four faces, making them ideal for compression members and bracing in portal frame structures. The Q235B grade serves general building frames where moderate yield strength suffices, while Q355B steps into heavier industrial platforms and solar mounting systems that demand higher section modulus. Our engineering team reviews project drawings to recommend the most efficient profile — for example, switching a 100×100×4.0 SHS to a 120×80×4.0 RHS can maintain the same moment resistance while reducing weight per meter. The Q235B Q355B square rectangular steel tube range covers 20×20mm through 500×500mm in square and up to 300×500mm in rectangular, with wall thickness from 1.2mm to 20mm, so specifiers rarely need to split orders across multiple suppliers.
Engineering Compliance Across EN, ASTM, and JIS Frameworks
International projects frequently require cross-standard grade substitution — a Middle East EPC may specify ASTM A500 Grade B while the design engineer references EN10219 S355JR in the same drawing set. Our mill maps Q235B to S235JR, A53 Grade B, A500 Grade A, and SS400 based on matching chemical composition and mechanical property envelopes, and Q355B to S355JR, A500 Grade B-C. This equivalence documentation satisfies both the local building authority and the international inspector without requiring separate material orders. [NEED_CITE: steel grade equivalence mapping between EN 10219 and ASTM A500 standards] For European market access, all hollow sections carry CE marking per EN10210 (hot-finished) or EN10219 (cold-formed), with factory production control audited to ISO 9001. Random lengths of 3m–12m ship efficiently in 20ft and 40ft containers, while cut-to-length options eliminate on-site cutting waste for projects with tight fabrication schedules.
Understanding Steel Grade Selection and ERW Welding Quality
The Q-series (Q195, Q235, Q355) follows the Chinese GB/T 6728 system where the number indicates nominal yield strength in MPa, directly paralleling the European S-series (S235JR, S355JR per EN10219) and the American A500 Grade system. For ERW welded hollow sections, the longitudinal seam undergoes online ultrasonic testing, and the weld zone is normalized during the hot-forming process to restore grain structure — this is critical for rectangular tubes where corner radii experience the highest forming strain. Surface treatment selection depends on the service environment: pre-galvanized coating at 40–80g/m² suits indoor structural frames and greenhouse skeletons, hot-dipped galvanizing at 200–600g/m² protects outdoor fencing and solar structures in coastal zones, and black hot-rolled finish serves projects where the tubes will receive shop-applied painting or fireproofing. Wall thickness tolerance of ±1% applies across the full 1.2mm–20mm range, verified by ultrasonic measurement at four points per cross-section. [NEED_CITE: ERW welded hollow section manufacturing process and weld integrity standards]
Hidden Costs of Sourcing Without Verified Material Traceability
Purchasing Q235B Q355B square rectangular steel tube without mill-direct traceability exposes projects to three compounding risks: material substitution where lower grades ship under higher-grade certificates, tolerance stacking where wall thickness consistently drifts to the negative boundary, and certification gaps where missing heat-number linkage causes customs holds or inspector rejection. On a warehouse project in West Africa, a batch of rectangular tubes arrived with MTC referencing a different heat number than the stencil on the steel — the entire lot failed the pre-installation audit and had to be air-freighted from an alternative source at triple the original cost. [NEED_CITE: structural steel material traceability requirements for international construction projects] These failures do not stem from the steel itself but from procurement channels that separate the material supplier from the fabricator, breaking the documentation chain at the most critical handoff point.
Procurement Confidence Through Vertical Integration
XJY Structure operates its own steel production facility with three rolling lines and maintains over 2,800 specifications of raw material in stock, meaning every Q235B Q355B square rectangular steel tube we deliver originates from a single quality system — no third-party material sourcing, no certificate chain gaps. Our in-house理化 laboratory issues Mill Test Certificates per EN 10204 3.1, covering chemical composition, tensile strength, and impact testing for every heat lot. Third-party inspection through SGS or BV is arranged before shipment at the buyer’s request, and our CE certification under EN10210 and EN10219 ensures customs clearance across EU member states without additional testing delays. For non-standard dimensions or project-specific cut lengths, our engineering team prepares shop drawings and material optimization plans before production begins, reducing waste and avoiding the dimensional errors that cause rework on the fabrication floor.
Documentation & Compliance
- Mill Test Certificate documenting Q235B/Q355B chemical composition, yield strength, and tensile properties per EN 10204 3.1, linked to heat number stenciled on each tube
- CE certificate confirming compliance with EN10219 for cold-formed structural hollow sections and EN10210 for hot-finished hollow sections, enabling EU customs clearance
- ISO 9001 quality management certificate covering the full production scope from raw material incoming inspection through final dimensional and coating verification
- SGS or BV third-party inspection report available upon request, covering wall thickness measurement, visual weld inspection, and coating thickness verification before container loading
- Material traceability report mapping each bundle to its original heat number, steel grade, and rolling date for project quality file submission
- Export documentation package including commercial invoice, packing list, bill of lading, and certificate of origin formatted for destination country customs requirements
Packaging, Loading & Delivery
- Q235B and Q355B square rectangular steel tubes bundled with galvanized steel strips at intervals no greater than 1.5m, with edge protectors applied to preserve pre-galvanized and hot-dipped zinc coatings during ocean transit
- Black hot-rolled tubes coated with anti-rust oil on inner and outer surfaces before bundling, preventing corrosion during extended container shipping to tropical and coastal project sites
- Container loading optimized by length: random 6m tubes load at approximately 18–20 tons per 20ft container, while 11.8m cut-to-length tubes maximize 40ft high-cube capacity with steel cradle support to prevent bending
- Cut-to-length service available across the 3m–12m range, with lengths marked by stenciled heat number, steel grade, and size designation on each piece for rapid identification at the fabrication yard
- Shipping terms available as FOB, CIF, or DDP to major ports across the Middle East, Southeast Asia, Africa, and South America, with professional lashing plans for oversized rectangular sections exceeding standard bundle dimensions
Start Your Project Inquiry With Verified Specifications
Submit your project drawings in PDF or DWG format along with the required steel grade, section dimensions, wall thickness, surface treatment preference, and total tonnage — our engineering team responds within 24 hours with a detailed quotation including material cost, fabrication scope, coating specification, and container loading plan. For projects requiring EN10219 or ASTM A500 compliance documentation, confirm the destination country and applicable building code at inquiry stage so we attach the correct CE marking and Mill Test Certificate format to your order.
Request Quotation and Material Certification
Share your project specifications, steel grade requirements, and destination port to receive a detailed quotation with Mill Test Certificate preview and production lead time. Contact XJY Structure via email at admin@xjystructure.com or WhatsApp at +86 188 5315 7756.
Frequently Asked Questions
Q: How do Q235B and Q355B map to European EN and American ASTM steel grades?
A: Q235B corresponds to S235JR under EN10219, A53 Grade B and A500 Grade A under ASTM, and SS400 under JIS G3466. Q355B maps to S355JR under EN10219 and A500 Grade B-C under ASTM, based on equivalent chemical composition and mechanical property ranges. We provide a formal grade equivalence table with each quotation for your engineer’s review.
Q: What test certificates are provided, and can third-party inspection be arranged?
A: Every shipment includes a Mill Test Certificate per EN 10204 3.1 covering chemical composition and mechanical properties, linked to the heat number marked on each tube. Third-party inspection through SGS or BV can be arranged before shipment at the buyer’s request, covering dimensional checks, coating thickness, and visual weld inspection.
Q: Can non-standard dimensions be produced, and what is the minimum order quantity?
A: Our mill covers square sections from 20×20mm to 500×500mm and rectangular sections from 20×40mm to 300×500mm, with wall thickness from 1.2mm to 20mm. The minimum order quantity is 1 Ton. For dimensions outside the standard range, our engineering team reviews feasibility based on tooling availability and provides a custom production plan.
Q: When should I specify pre-galvanized versus hot-dipped galvanized versus black finish?
A: Pre-galvanized coating at 40–80g/m² is suitable for indoor structural frames, greenhouse skeletons, and light corrosion environments. Hot-dipped galvanizing at 200–600g/m² is recommended for outdoor applications including solar mounting structures, fencing systems, and coastal infrastructure. Black hot-rolled finish is specified when the tubes will receive shop-applied painting, powder coating, or fireproofing at the fabrication stage.
Q: How are the tubes packed and loaded for export, and what lengths fit each container?
A: Tubes are bundled with galvanized steel strips and edge protectors to preserve surface coating. Random 6m lengths load approximately 18–20 tons per 20ft container, while 11.8m cut-to-length tubes maximize 40ft high-cube capacity. Oversized rectangular sections receive custom steel cradle support to prevent deformation during transit.
