Description
Direct Mill Supply, No Broker Markup — Every Q235 Q345 S355 Carbon Steel Square Steel Tube Manufacturer order rolls from our own 3-line steel mill in Jinan, backed by 2,800+ raw material specs and in-house chemical and mechanical testing.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Steel Square Steel Tube |
| Product Type | Square / Rectangular Hollow Section (SHS / RHS) |
| Steel Grade | Q235, Q235B, Q345, Q345B, SS400, S235JR, S275JR, S355J2, ASTM A53, ASTM A106 |
| Standard | GB/T 6728, EN 10219, EN 10210, ASTM A53, ASTM A106, API 5L, JIS G3466 |
| Section Shape | Square / Rectangular |
| Size Range | 15mm × 15mm – 800mm × 800mm |
| Wall Thickness | 1mm – 50mm |
| Length | 6000mm / 12000mm (customizable) |
| Technique | ERW / Hot Rolled / Cold Rolled |
| Surface Treatment | Black Painted / Varnished / Hot-Dip Galvanized / Electro-Galvanized / 3LPE / 3LPP Coated / Oiled |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures, construction frameworks, scaffolding, oil & gas pipelines, machinery, automotive chassis, shipbuilding |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building columns and beams, structural frameworks, scaffolding systems, warehouse portal frames |
| Industrial & Energy | Oil & gas pipeline supports, hydraulic and pneumatic machinery frames, offshore platform bracing |
| EPC & General Contracting | Turnkey structural steel supply for factories, logistics centers, and commercial buildings |
What Negative Tolerance Really Costs on a Square Tube Order
A ±1% wall thickness tolerance means what the drawing says is what the beam carries.
Overseas buyers ordering carbon steel square steel tube from overseas fabricators routinely discover that the theoretical weight on the packing list does not match the weighbridge at destination port. When wall thickness is pushed to the negative extreme, the load-bearing cross-section shrinks — and structural engineers cannot sign off. We have seen entire container loads rejected at third-party re-inspection because the actual mass fell outside the tolerance band allowed by EN 10219. The cost is not just the steel; it is demurrage, re-procurement, and a delayed erection schedule. [NEED_CITE: EN 10219 cold-formed structural hollow section tolerance requirements]
Matching Section Geometry to Structural Load Paths
Square and rectangular hollow sections distribute stress evenly across all four faces, making them ideal for compression members and moment-resisting frames. Our Q235 Q345 S355 Carbon Steel Square Steel Tube Manufacturer range covers 15mm × 15mm through 800mm × 800mm with wall thickness from 1mm to 50mm, so a single procurement package can cover light-gauge purlins and heavy-load base columns alike. The ±1% tolerance on wall thickness ensures that connection design — whether bolted end-plates or full-penetration welds — performs as the structural model predicts.
Engineering Compliance Across Destination Markets
Structural hollow sections shipped to the EU must carry CE marking under EN 10210 (hot-finished) or EN 10219 (cold-formed), with Factory Production Control audited to ISO 9001. Projects in North America reference ASTM A500 or ASTM A53, while Middle East and African EPC contracts frequently accept GB/T 6728 or JIS G3466 with mill test certificates cross-referenced to heat numbers. [NEED_CITE: steel grade equivalence mapping between GB, EN, and ASTM standards] Selecting the correct standard at the inquiry stage avoids customs holds and eliminates the need for duplicate testing at the destination port.
Steel Grade Selection and Forming Process Explained
The Q-series (Q235, Q345) follows the Chinese GB system where the number denotes minimum yield strength in MPa; the S-series (S235JR, S275JR, S355J2) follows the European EN system with impact-energy suffixes indicating low-temperature toughness; ASTM A53 and A106 serve pressure and mechanical applications in North American specs. ERW (Electric Resistance Welded) tubes suit general structural use at competitive cost, while hot-rolled sections offer superior corner radii for heavy-load columns, and cold-rolled sections deliver tighter dimensional accuracy for architectural exposure. Surface treatment selection follows the service environment: hot-dip galvanizing for outdoor or coastal exposure, 3LPE/3LPP coating for buried or submerged pipeline supports, and black painted or oiled finish for indoor or temporary structures. Wall thickness directly governs load capacity — a 10mm wall on a 200mm SHS carries substantially more than a 6mm wall of the same outer dimension, and the ±1% tolerance ensures the design assumption holds in practice.
The Hidden Price of Unverified Material
Ordering carbon steel square steel tube without verified mill test certificates or third-party inspection creates a chain of risk: material that fails chemical composition limits cannot be welded to code; wall thickness below tolerance triggers structural rejection; missing CE or ASTM documentation blocks customs clearance. The engineering norm is clear — every heat of steel must be traceable from mill slab to finished tube, with mechanical and chemical results documented per the applicable standard. [NEED_CITE: material traceability and MTC requirements in structural steel procurement]
Why Buyers Consolidate with Our Mill
As a vertically integrated carbon steel square steel tube manufacturer, we control the entire chain from raw coil to finished section. Our Jinan facility operates 3 production lines covering ERW, hot-rolled, and cold-formed processes, with 2,800+ raw material specifications in stock — meaning non-standard sizes and mixed-grade orders ship from a single source. Every heat is tested in our in-house laboratory for chemical composition and mechanical properties, and mill test certificates are issued per heat number. We hold CE certification for EN 10210 and EN 10219, ISO 9001 quality management, and welcome SGS, BV, or TUV third-party inspection before shipment. Our professional loading team handles oversized sections and custom-length bundles, optimizing container utilization for 6m and 12m lengths.
Documentation & Compliance
- Mill Test Certificate documenting Q235B and Q345B chemical composition and yield strength per GB/T 6728, or S235JR/S355J2 per EN 10219
- CE certificate confirming compliance with EN 10210 (hot-finished) and EN 10219 (cold-formed) structural hollow sections for EU market access
- ISO 9001 quality management certificate covering the full fabrication and testing process at our Jinan mill
- SGS or BV third-party inspection report available upon request, covering dimensional checks, coating thickness, and weld integrity
- Full material traceability by heat number from raw coil to finished square tube, cross-referenced on every MTC
- Export customs documentation including packing list, bill of lading, and certificate of origin for destination clearance
Packaging, Loading & Delivery
- Hot-dip galvanized Q235 and Q345 square tubes bundled with soft-edge protectors and waterproof wrapping to preserve the zinc coating during ocean transit
- Black painted and oiled S235JR/S355J2 sections strapped in steel-strip bundles with dunnage separation to prevent surface damage and allow forklift handling
- 6m and 12m lengths loaded into 20ft and 40ft containers with optimized nesting for square and rectangular sections, maximizing payload per shipment
- Custom cut-to-length service available for non-standard project dimensions, with plain ends deburred and marked with heat number, steel grade, and size
- Heat number and steel grade stenciled on each bundle for site identification and traceability verification upon arrival
- FOB, CIF, and DDP terms available with door-to-door logistics coordination for EPC project sites across the Middle East, Southeast Asia, and Africa
Start Your Procurement with Drawings and Specs
Submit your project drawings (PDF or DWG), required steel grades, section sizes, wall thickness, surface treatment, and destination port — we respond within 24 hours with a detailed quotation, shop drawing timeline, and production schedule. For non-standard dimensions or mixed-grade orders, our engineering team will confirm feasibility and lead time before contract. All orders include mill test certificates and export documentation as standard, with third-party inspection available at your request.
Frequently Asked Questions
Q: How do Q235/Q345 (GB) grades map to S235JR/S355J2 (EN) and ASTM equivalents?
A: Q235 corresponds broadly to S235JR and ASTM A36 in yield strength range; Q345 maps to S355J2 and ASTM A572 Grade 50. We provide cross-reference documentation with every order to support engineering approval and customs clearance.
Q: Can you provide mill test certificates and support third-party re-inspection?
A: Yes. Every heat of steel is tested in our in-house laboratory, and MTCs are issued per heat number. SGS, BV, and TUV inspections are available before shipment at the buyer’s request.
Q: What is the minimum order quantity for non-standard sizes?
A: Standard sizes from our 2,800+ specification range ship with no minimum order constraint. For custom dimensions outside standard range, MOQ is confirmed during quotation based on mill scheduling.
Q: When should I specify hot-dip galvanized versus 3LPE coating versus painted finish?
A: Hot-dip galvanizing suits outdoor and coastal exposure; 3LPE/3LPP coating is specified for buried or submerged pipeline supports; black painted or oiled finish is appropriate for indoor or temporary structures where corrosion protection is not critical.
Q: How do you handle packing and container loading for oversized square tubes?
A: Our loading team specializes in oversized and heavy-section packing. Square and rectangular sections are nested and dunnaged to maximize container payload, with edge protection for galvanized finishes and steel-strip bundling for all surface types.
[Request Your Quotation and Mill Test Certificates Today]
Send your drawings, specifications, and destination port to receive a detailed quotation with production schedule and full documentation package.
Contact: admin@xjystructure.com | WhatsApp: +86 188 5315 7756 | Tel: +86 531 8573 6315
