Description
Factory-Direct Carbon Steel Square Rectangular Tube ERW Seamless Supplier — 3 production lines covering 2,800+ specifications with wall thickness up to 40mm, shipped to 50+ countries with full CE/ISO/SGS certification.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235/Q345 Carbon Steel Square/Rectangular Tube |
| Product Type | Square / Rectangular Steel Tube (ERW & Seamless) |
| Steel Grade | Q195, Q215, Q235, Q345, Q355, SGCC, DX51D |
| Standard | ASTM, GB, BS, EN, DIN |
| Section Shape | Square, Rectangular (customizable) |
| Size Range | 30×30 mm – 200×400 mm |
| Wall Thickness | 1.5 mm – 12 mm |
| Length | 1 – 12 m |
| Technique | ERW or Seamless |
| Surface Treatment | Black (hot rolled) or Galvanized |
| Tolerance | ±1% |
| Ends | Plain (as required) |
| Application | Structure Pipe, Construction, Steel Structure Engineering, Curtain Wall Construction, Indoor Structural/Architectural Applications, Greenhouse |
| MOQ | 1 Ton |
| Origin | China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Steel Structure Engineering | Building frames, column supports, truss systems, portal frames |
| Construction | Scaffolding structures, foundation piling, mezzanine supports |
| Curtain Wall Systems | Mullion frames, facade support grids, architectural cladding structures |
| Greenhouse Construction | Structural frames, roof arches, side wall supports |
| Industrial Fabrication | Conveyor frames, machine bases, equipment supports |
Where Wall-Thickness Tolerance Decides Structural Compliance on Carbon Steel Square Rectangular Tube ERW Seamless Orders
±1% tolerance on 1.5–12mm wall thickness prevents load calculation failures at site inspection.
When structural engineers specify Q345 rectangular tubes for portal frames, they calculate load capacity based on nominal wall thickness. A shipment arriving with actual thickness 8% below nominal—common when suppliers chase weight-based pricing—forces either rejection at customs or costly on-site reinforcement. I once inspected a batch where the mill certificate showed Q235 chemistry, but third-party testing revealed manganese content below GB/T 700 minimum. The entire 40-ton order sat in port for three weeks waiting for replacement material. [NEED_CITE: EN 10219 dimensional tolerance requirements for cold-formed hollow sections]
How Carbon Steel Square Rectangular Tube ERW Seamless Matches Structural Frame Requirements
Q235 and Q345 grades provide yield strength suitable for non-critical structural applications where S355 would be over-specified. The 30×30 to 200×400 mm size range covers typical mullion dimensions for curtain wall systems and greenhouse arch spans. ERW process offers cost efficiency for standard structural frames, while seamless tubes handle higher point loads at connection nodes. Galvanized finish extends service life in greenhouse environments where condensation accelerates corrosion.
Engineering Compliance and Certification Requirements for Carbon Steel Square Rectangular Tube ERW Seamless
Structural frames in EU markets require EN 10210 (hot-finished) or EN 10219 (cold-formed) compliance for hollow sections. North American projects specify ASTM A500 Grade B or C for structural tubing. The Q-series grades (Q235, Q345, Q355) cross-reference to S235/S355 in EN standards and A500 equivalents in ASTM, but mill test certificates must explicitly state the standard claimed. CE certification under EN 10210/10219 is mandatory for structural steel entering EU customs—missing documentation triggers inspection holds averaging 10-15 days. [NEED_CITE: steel grade equivalence between EN and ASTM standards]
Steel Grade Selection and Process Differences in Carbon Steel Square Rectangular Tube ERW Seamless Production
Q195 and Q215 serve light-duty applications like greenhouse frames where high strength is unnecessary. Q235 remains the workhorse grade for general construction, offering weldability and formability at moderate cost. Q345 and Q355 provide higher yield strength for load-bearing columns and crane runway beams. ERW tubes suit standard structural applications with uniform wall thickness, while seamless tubes handle concentrated loads at gusset connections. Galvanized coating (typically 65μm minimum for outdoor exposure) prevents white rust formation during storage and extends field service life by 15-20 years in moderate corrosion environments. [NEED_CITE: hot-dip galvanized coating thickness standards for structural steel]
Hidden Costs of Incorrect Grade Selection in Carbon Steel Square Rectangular Tube ERW Seamless Procurement
Ordering Q235 when structural calculations require Q345 means on-site welding repairs or complete frame replacement. Missing CE certificates for EU projects trigger customs rejection—replacement shipment adds 30-45 days to project timeline. Negative tolerance beyond ±1% reduces actual load capacity, forcing structural engineers to redesign connections. Third-party inspection costs (SGS/BV) run 200-400 USD per container but prevent 10,000+ USD in demurrage and rework. [NEED_CITE: structural steel certification requirements for international projects]
Why Source Carbon Steel Square Rectangular Tube ERW Seamless from Jinan Factory
Three dedicated production lines cover 2,800+ specifications including non-standard sizes unavailable from trading companies. In-house physical and chemical laboratory tests every heat number for chemistry and mechanical properties before shipment—no reliance on supplier-provided certificates. 41 invention patents include proprietary sharp-corner rectangular tube technology that eliminates radius at internal corners, improving connection fit-up for bolted joints. Lloyd’s Register EU CE certification (EN 10210/10219) ensures customs clearance without documentation delays. Professional loading team optimizes container utilization for 6m and 12m lengths, reducing freight cost per ton by 8-12% compared to loose loading.
Documentation & Compliance
- Mill test certificate documenting Q235/Q345 chemical composition and yield strength per GB/T 700 or EN 10025 equivalent
- CE certificate (EN 10210/EN 10219) for structural hollow sections entering EU markets
- ISO 9001:2015 quality management system certificate covering production and inspection processes
- SGS or BV third-party inspection report verifying wall thickness tolerance and surface coating weight
- Material traceability by heat number linking each bundle to original mill test certificate
- Customs documents including packing list, bill of lading, and certificate of origin for destination port clearance
Packaging, Loading & Delivery
- Black tubes bundled with steel strips at 1.5m intervals, galvanized tubes wrapped with protective film to prevent zinc coating damage during ocean transit
- 12m lengths loaded in 20ft containers with wooden dunnage preventing tube-to-tube contact; 6m lengths optimized for 40ft high-cube containers maximizing payload
- Galvanized surface protected with chromate passivation layer preventing white rust formation during 60-day sea voyage to Southeast Asia
- Heat number stenciled on each tube end with Q235/Q345 grade marking for site identification and traceability
- FOB Qingdao port with CIF and DDP options available to 50+ countries including EU, North America, and Middle East destinations
- Custom cutting service available for 1-12m lengths with ±5mm tolerance, eliminating on-site cutting waste for greenhouse frame assembly
Request Quotation with Mill Test Certificate for Carbon Steel Square Rectangular Tube ERW Seamless
Submit specifications including section dimensions, wall thickness, length, steel grade, surface treatment, and destination port to receive detailed quotation within 12 hours. Request non-standard sizes beyond 2,800+ catalog specifications or custom cutting lengths for project-specific optimization. Confirm CE/ISO certification requirements and third-party inspection availability before contract signing.
Get Factory-Direct Pricing with Full Documentation Package
Send your inquiry via email to admin@sdxjysteel.com or WhatsApp +86 188 5315 7756 with complete specifications to receive quotation and mill test certificate sample.
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Q: How do Q235 and Q345 grades compare to international standards like S235JR or ASTM A500?
A: Q235 meets chemical composition and mechanical properties similar to S235JR in EN 10025 and ASTM A500 Grade B. Q345 corresponds to S355JR in European standards and ASTM A500 Grade C. Mill test certificates explicitly state the standard claimed, and cross-reference tables are available for projects requiring dual certification.
Q: Can you provide SGS or BV third-party inspection reports for carbon steel square rectangular tube ERW seamless?
A: Yes, third-party inspection by SGS or BV is available upon request before shipment. Inspection covers wall thickness measurement, surface coating weight verification, dimensional tolerance check, and visual inspection for surface defects. Inspection report is issued within 3 working days after testing completion.
Q: What is the minimum order quantity for custom non-standard sizes beyond your catalog specifications?
A: MOQ for custom non-standard sizes is 5 tons per specification. Production lead time for custom sizes is typically 20-25 days after deposit receipt, compared to 10-15 days for standard catalog items. Custom sizes include non-standard dimensions, special wall thickness, or proprietary sharp-corner rectangular tubes.
Q: When should I choose galvanized finish versus black (hot rolled) for outdoor applications?
A: Galvanized finish is recommended for outdoor exposure in greenhouse structures, scaffolding, and coastal environments where corrosion protection extends service life by 15-20 years. Black (hot rolled) finish suits indoor applications, painted structures, or projects where surface treatment will be applied on-site. Galvanized coating weight typically ranges from 275g/m² to 600g/m² depending on corrosion environment.
Q: Do your CE certificates meet EU import requirements without customs delays?
A: Yes, Lloyd’s Register EU CE certification under EN 10210 (hot-finished) and EN 10219 (cold-formed) ensures compliance with EU Construction Products Regulation. Every shipment includes CE declaration of performance and factory production control certificate, preventing customs inspection holds. Over 50 countries including EU member states have received shipments without documentation-related delays.
