Description
Factory-Direct ERW Square Tubes — 3 production lines running Q235, Q345, and S355 grades from 15×15mm to 800×800mm with original mill test certificates on every batch.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235 Q345 S355 Carbon Steel Square Pipe |
| Product Type | Square Steel Tube (Welded / ERW) |
| Steel Grade | Q235, Q235B, Q345, Q345B, S235JR, S275JR, S355J2, SS400, ASTM A53, ASTM A106, API 5L (Gr.A, Gr.B, X42, X52, X60, X70) |
| Standard | ASTM A53, ASTM A106, API 5L, EN 10219, GB/T 6728, JIS G3466 |
| Section Shape | Square / Rectangular |
| Size Range | 15mm × 15mm – 800mm × 800mm |
| Wall Thickness | 1mm – 50mm (or Customized) |
| Length | 6000mm / 12000mm (or Customized) |
| Technique | ERW / Hot Rolled / Cold Rolled |
| Surface Treatment | Black Painted / Varnished / Galvanized (Hot-Dip / Electro) / 3LPE / 3LPP Coated / Oiled |
| Tolerance | ±1% |
| Ends | Plain / Beveled (per customer requirement) |
| Application | Construction, Oil & Gas, Automotive, Machinery, Shipbuilding |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Structural frameworks, scaffolding systems, building frames for Belt & Road projects |
| Oil & Gas | Pipeline transmission lines, drilling platform support structures |
| Machinery | Hydraulic cylinder housings, pneumatic system frames, conveyor structures |
| Shipbuilding | Marine piping supports, offshore platform structural members |
| Automotive | Chassis components, exhaust system brackets |
What Negative Wall Tolerance Costs on a Structural Frame Order
A 5% negative tolerance deviation on a 50-ton square tube order means 2.5 tons of missing steel — paid for but never delivered.
Early in my career, a batch of 40×40 square tubes arrived at a project site in Southeast Asia. The wall thickness ran consistently below the lower limit of the specified tolerance range. Theoretical weight and actual weighbridge readings differed by over 2 tons per container. The entire lot was rejected, re-inspected, and reordered — delaying the project by weeks. When sourcing an ASTM Q235 Q345 S355 carbon steel square tube supplier, buyers must verify that tolerance claims are backed by measurable quality control, not just catalog statements [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements].
Matching Square Tube Dimensions to Structural Load Requirements
The 15×15mm to 800×800mm side length range covers everything from light-duty machinery frames to heavy structural columns. Wall thickness from 1mm to 50mm allows engineers to balance load-bearing capacity against weight constraints. For scaffolding and building frameworks, Q235 and S235JR grades provide adequate yield strength at lower cost. For pressure-containing applications in oil and gas, API 5L grades from Gr.B through X70 meet pipeline transmission standards. Our 3 production lines maintain ready stock across 2,800+ specifications, so standard sizes ship immediately while custom dimensions follow typical production lead times.
Engineering Compliance and Certification for Global Projects
Structural steel hollow sections used in construction must comply with EN 10219 for cold-formed welded sections or EN 10210 for hot-formed finished hollow sections in European markets. North American projects typically require ASTM A500 or ASTM A53 compliance. Shipbuilding and offshore applications demand classification society certification. Every batch of Q235 Q345 S355 carbon steel square tube we supply ships with original mill test certificates documenting chemical composition and mechanical properties per the relevant standard. Lloyd’s CE certification under EN 10210/10219 and FPC certification ensure customs clearance across EU member states [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 10210].
Steel Grade Selection and ERW Manufacturing Fundamentals
The Q-series (Q235, Q345) follows the Chinese GB/T 6728 standard, where the number indicates minimum yield strength in MPa. The S-series (S235JR, S275JR, S355J2) follows EN 10219, with JR denoting room-temperature impact testing and J2 indicating sub-zero impact testing at −20°C. ASTM A53 and A106 serve pressure and mechanical applications in North American markets. API 5L grades from Gr.A through X70 cover pipeline transmission with increasing tensile requirements. ERW (Electric Resistance Welded) manufacturing forms steel coil into square or rectangular cross-sections and welds the seam through electrical resistance heating — producing consistent wall thickness and dimensional accuracy at lower cost than seamless alternatives for structural applications. Surface treatment selection depends on the operating environment: black painted or oiled for indoor or temporary protection, hot-dip galvanized for atmospheric corrosion resistance, and 3LPE/3LPP coated for buried or submerged conditions.
Hidden Costs of Unverified Steel Procurement
Pricing that appears competitive often reflects corner-cutting elsewhere: undersized wall thickness, untraceable material origins, or missing certification documents. When steel grade does not match the specified standard, structural engineers cannot verify load calculations. When mill test certificates are absent or fabricated, customs authorities hold shipments at the port. When negative tolerance exceeds acceptable limits, the buyer pays for steel that was never shipped — and faces structural safety risks on site. An ASTM Q235 Q345 S355 carbon steel square tube supplier who cannot provide heat-number traceability and third-party inspection reports transfers all quality risk to the buyer [NEED_CITE: consequences of non-compliant structural steel in construction projects].
Why Project Buyers Source ERW Square Tubes Through Our Mill
We operate 3 production lines in Jinan with monthly capacity exceeding 20,000 tons, supplying factory-direct pricing without intermediary margins. Every heat of steel carries a unique identification number, and our in-house laboratory conducts three-stage inspection before release. Buyers sourcing Q235 Q345 S355 carbon steel square tube receive original mill test certificates with each shipment — not photocopies, not templates. For buyers requiring independent verification, SGS or BV third-party inspection is available at the production stage. Our export team handles container loading optimization, consolidating multiple specifications into single shipments to reduce freight cost per ton. Long-term partners receive volume-based discount reviews every 6 months, and flexible MOQ from 1 ton supports both trial orders and full-container bulk procurement.
Documentation & Compliance
- Mill test certificate documenting Q235/Q345/S355 chemical composition and mechanical properties per GB/T 6728, EN 10219, or ASTM A53 as specified
- CE certificate under EN 10210/EN 10219 for structural hollow sections entering European Union markets
- ISO 9001:2015 quality management certificate covering production processes and inspection procedures
- SGS or BV third-party inspection report available upon request for independent quality verification
- Full material traceability by heat number linking each tube to its original steel coil and production batch
- Complete customs documentation including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- ERW square tubes bundled with steel strips and edge protectors to prevent surface damage during ocean transit, with bundle weight optimized for container crane handling
- Black painted or oiled surfaces wrapped in waterproof paper; galvanized tubes separated by protective spacers to preserve zinc coating integrity
- Container loading plans optimized for 6000mm and 12000mm lengths to maximize payload per 20ft or 40ft container, reducing freight cost per ton
- Custom cut-to-length service available for 15×15mm through 800×800mm sections, with kerf loss minimized through nested cutting plans
- Heat number and steel grade stenciled on each tube end for site identification and traceability verification
- FOB, CIF, and DDP shipping terms available with professional export documentation handling for ports across 50+ countries
Requesting a Quotation for Your Project Requirements
Submit your specifications including side length, wall thickness, steel grade, total quantity, and destination port to receive a competitive bulk quotation with volume discounts. For non-standard dimensions or custom lengths outside the 15×15mm to 800×800mm range, our technical team provides feasibility assessment and production scheduling. Confirm certification requirements and third-party inspection needs before contract signing to ensure compliance with your project specifications.
Frequently Asked Questions
Q: How do Q235 and Q345 grades compare to S235JR and S355J2 under EN 10219?
A: Q235 and S235JR offer comparable minimum yield strength for general structural applications, while Q345 and S355J2 provide higher yield strength for heavier load requirements. The J2 designation indicates impact testing at −20°C, making S355J2 suitable for cold-climate projects. Both grade systems are widely accepted in international procurement, and our mill test certificates document compliance with the specified standard.
Q: Can you provide mill test certificates and arrange third-party inspection?
A: Every batch of Q235 Q345 S355 carbon steel square tube ships with original mill test certificates documenting chemical composition and mechanical properties. SGS or BV third-party inspection is available at the production stage for buyers requiring independent verification before shipment.
Q: What is the minimum order quantity for non-standard sizes and custom lengths?
A: Our flexible MOQ starts from 1 ton, supporting both trial orders for specification verification and full-container bulk procurement. Custom lengths outside standard 6000mm and 12000mm are available based on production scheduling and order volume.
Q: When should I specify galvanized versus black painted or 3LPE coated surface treatment?
A: Hot-dip galvanized coating provides long-term atmospheric corrosion resistance for outdoor structural applications. Black painted or oiled surfaces suit indoor environments or temporary protection during construction. 3LPE and 3LPP coatings are specified for buried pipelines or submerged marine conditions requiring enhanced corrosion protection.
Q: What production lead times and shipping options are available?
A: Standard specifications from our ready stock of 2,800+ sizes ship within typical production lead times. Custom orders follow standard scheduling based on specification complexity and order volume. FOB, CIF, and DDP terms are available with professional export documentation handling.
[Start Your Bulk Procurement Today]
Submit your ASTM Q235 Q345 S355 carbon steel square tube specifications via email or WhatsApp to receive a factory-direct quotation with mill test certificate confirmation within 12 hours.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxinjiyuan.com
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxinjiyuan.com
