Description
Factory-Direct Welded Tubes — Bulk carbon steel square and rectangular pipes produced in-house with original mill test certificates and no trading markup.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Steel Square Pipe Tube |
| Product Type | Square / Rectangular Steel Tube (Welded) |
| Steel Grade | Q195, Q215, Q235, Q345, #20, #45, S235JR, S355JR, A53 Grade A, A53 Grade B, A500 Grade A, A500 Grade B, A500 Grade C, STK400, SS400, ST42.2, S195, S355J2H, S355J0H |
| Standard | EN10219, EN10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A53, ASTM A36 |
| Section Shape | Square / Rectangular |
| Size Range | Square: 20×20mm – 500×500mm; Rectangular: 20×40mm – 300×500mm |
| Wall Thickness | 0.5 – 30mm |
| Length | 3m – 12m (random / customized) |
| Technique | Welded (Hot Rolled Hollow Carbon Pipe) |
| Surface Treatment | Black / Pre-galvanized (40–80g/m²) / Hot-dip galvanized (200–600g/m²) |
| Tolerance | ±1% |
| Ends | Plain |
| Processing Service | Bending, Welding, Decoiling, Punching, Cutting |
| Invoicing | By Actual Weight |
| Application | Construction, Structural Frames, Solar Structures, Fencing, Greenhouse, Machinery, Shipbuilding, Power Engineering, Curtain Wall, Automobile Chassis, Airport, Highway, Housing, Pressure Vessels, Oil Tanks, Bridges, Lifting Machinery |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building structural frames, highway guardrail posts, bridge support members, housing skeleton columns |
| Energy & Industrial | Solar panel mounting structures, greenhouse framing, power transmission tower bracing, pressure vessel shells |
| Machinery & Transportation | Automobile chassis cross-members, lifting equipment booms, shipbuilding deck structures, conveyor support frames |
| Commercial & Public Works | Airport terminal roof trusses, glass curtain wall mullions, fence and barrier systems |
Where Negative Tolerance Turns a Cheap Quote into a Costly Rework
A ±1% tolerance on a 500×500×20mm Customized Carbon Steel Square Pipe Tube Manufacturer order means every piece must hit the drawing — not the scrap bin.
Structural engineers design connection plates and gusset dimensions to the mill’s published tolerance band. When a supplier ships tubes that consistently ride the lower edge of wall thickness — or worse, fall outside the declared range — field fitters spend days grinding, shimming, or re-welding joints that should have bolted together on the first attempt. On a solar racking project in West Africa, I watched a crew reject an entire container because the rectangular tubes measured under-spec at every corner joint; the zinc coating had cracked during forming because the base metal was too thin to hold the bend radius. [NEED_CITE: EN 10219 dimensional tolerance requirements for cold-formed hollow sections]
Matching Section Geometry to Load Paths in Structural Frames
A Customized Carbon Steel Square Pipe Tube Manufacturer that understands load-path logic stocks both square and rectangular sections because the two shapes serve fundamentally different structural roles. Square tubes distribute compression evenly across all four faces, making them the default choice for vertical columns in building frames and greenhouse structures. Rectangular tubes — particularly the 20×40mm to 300×500mm range — place more material along the major axis, giving higher moment of inertia for beams and horizontal bracing where bending resistance matters more than uniform compression. On a warehouse project in Dubai, we supplied Q345 rectangular tubes at 150×300×8mm for the main roof rafters while matching Q345 square tubes at 200×200×10mm for the column grid; the mixed-section approach cut steel tonnage by roughly 12% versus using a single oversized profile.
Engineering Compliance Across EN, ASTM, and JIS Frameworks
Project specifications in the EU demand CE-marked hollow sections conforming to EN 10219 or EN 10210, and customs authorities in Rotterdam and Hamburg routinely hold shipments that lack the Declaration of Performance. North American EPCs specify ASTM A500 Grade B or C for structural tubing, while Japanese-designed infrastructure projects across Southeast Asia call for JIS G3466 STK400. A Customized Carbon Steel Square Pipe Tube Manufacturer serving these markets simultaneously must maintain certified production lines for each standard and keep mill test certificates organized by heat number so that auditors can trace any single tube back to its original coil. Third-party inspection by SGS or BV before loading closes the documentation gap that causes the most frequent customs delays. [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 10210]
Steel Grade Selection: Q-Series, S-Series, and ASTM Equivalents
The Q-series grades (Q195 through Q345) follow the Chinese GB/T 700 system where the number indicates minimum yield strength in MPa; Q235 remains the workhorse grade for general construction across Africa and the Middle East because it balances formability with adequate structural capacity. The European S-series (S235JR, S355JR, S355J2H, S355J0H) adds impact-toughness designations — the “JR” suffix guarantees 27J Charpy impact energy at +20°C, while “J2H” pushes that guarantee to −20°C, a critical distinction for projects in Scandinavia or high-altitude sites. ASTM A500 Grades A, B, and C step up yield and tensile requirements progressively, with Grade C commonly specified for welded structural connections in the United States. Cross-referencing these systems — Q345 roughly maps to S355JR and A500 Grade C — lets procurement teams source a single Customized Carbon Steel Square Pipe Tube Manufacturer rather than splitting orders across three mills. Surface treatment choice follows the environment: black (oiled) tubes suit indoor structural frames where painting will occur on-site; pre-galvanized at 40–80g/m² handles moderate outdoor exposure for fencing and greenhouse frames; hot-dip galvanized at 200–600g/m² is mandatory for highway railings, coastal solar structures, and any application where maintenance access is limited.
The Hidden Price of Unverified Mill Certificates
Accepting a lower unit price from a supplier who cannot produce heat-number-traceable mill test certificates shifts cost downstream in ways that rarely appear on the initial quotation. Without verified chemical composition and mechanical property data, the buyer carries the risk that weld procedure qualifications will fail during inspector witness testing — a scenario that halts erection and forces either full-batch re-testing or outright rejection. [NEED_CITE: structural steel weld procedure qualification requirements under EN 1090-2] Missing CE documentation for EN 10219 tubes entering the EU triggers customs holds that incur demurrage charges exceeding the original freight cost. And when wall thickness falls below the tolerance band declared on the purchase order, the structural engineer of record must either redesign the connection or order replacement material, turning a procurement saving into a multi-week schedule delay.
Why Procurement Teams Return for Repeat Orders
We run three production lines simultaneously, producing over 20,000 tons monthly, which means a 50-ton order of Q235B square tubes ships from existing stock while a custom 150×300×6mm rectangular tube in S355J2H rolls through the mill within typical production lead times. Every heat is tested in our in-house laboratory, and the resulting mill test certificate travels with the shipment — no certificate means no loading, full stop. Buyers who consolidate square tubes, rectangular tubes, H-beams, and steel plates into a single container save on freight and reduce the coordination overhead of managing multiple suppliers. We handle the loading plan ourselves: after the carbon steel square pipe tube loading incident I mentioned earlier, every container gets a custom bracing and blocking scheme drawn before the first piece enters the door. SGS and BV inspections are arranged on-site at the buyer’s request, and our export team prepares the full customs documentation package — packing list, bill of lading, certificate of origin, and CE Declaration of Performance — so that the cargo clears at destination without the buyer’s forwarding agent chasing missing papers.
Documentation & Compliance
- Mill test certificate documenting Q235B / S355JR chemical composition and mechanical properties per EN 10219, traceable to heat number
- CE certificate covering EN 10210 and EN 10219 structural hollow sections for EU customs and project compliance
- ISO 9001:2015 quality management certificate covering the full production and inspection process
- SGS or BV third-party inspection report available upon request, covering dimensional checks, surface quality, and witness testing
- Material traceability report linking each bundle to its heat number, coil origin, and production date
- Export customs documents including packing list, ocean bill of lading, certificate of origin, and CE Declaration of Performance
Packaging, Loading & Delivery
- Welded carbon steel square and rectangular tubes bundled with high-tensile steel strips; bundles sized to match container payload limits for 20ft and 40ft GP or OT units
- Hot-dip galvanized tubes (200–600g/m²) wrapped with rubber edge protectors at every contact point to prevent zinc coating damage during ocean transit
- Pre-galvanized tubes (40–80g/m²) bundled with interleaved plastic sheeting to block moisture condensation inside the container
- Custom-length tubes cut to 3m–12m per order; ends capped or wrapped to protect plain-end bevelling during handling
- Each bundle tagged with heat number, steel grade (e.g., Q345 / S355JR), and dimension label for on-site identification
- FOB, CIF, and DDP terms available; container loading plans optimized to maximize payload for mixed-size shipments of square and rectangular sections
Starting Your Procurement Cycle
Send your specification sheet — section dimensions, wall thickness, steel grade, surface treatment, quantity, and destination port — and we return a detailed quotation with FOB/CIF pricing, typical production lead times, and a sample mill test certificate format within 12 hours. For non-standard dimensions outside the 20×20mm to 500×500mm range, we provide a custom rolling feasibility review and tooling timeline before you commit.
Request a Quote with Mill Test Certificate
Submit your Customized Carbon Steel Square Pipe Tube Manufacturer requirements via email at admin@sdxinjiyuan.com or WhatsApp at +86 188 5315 7756 to receive pricing, material documentation, and loading plans.
Frequently Asked Questions
Q: How do Q235B, S235JR, and ASTM A53 Grade B compare for structural use?
A: Q235B (GB/T 700) and S235JR (EN 10025) offer similar yield strength levels and are both widely used for general construction frames; ASTM A53 Grade B is a pipe-grade specification with slightly different chemical limits, typically specified for pressure and mechanical applications. For structural hollow sections in the EU, S355JR per EN 10219 is the standard upgrade. We supply all three grade families from the same production lines and provide cross-reference documentation on request.
Q: What mill test certificates and third-party inspections do you provide?
A: Every shipment includes an original mill test certificate showing chemical composition and mechanical properties, traceable to the heat number. SGS or BV third-party inspection can be arranged before loading to verify dimensions, surface quality, and coating thickness — the inspection report is issued on-site and included in the shipping document package.
Q: Can I order non-standard sizes or small quantities?
A: Yes. Our stock covers 2,800+ standard specifications in square and rectangular sections, and we accept trial orders from 1 Ton. For non-standard dimensions or custom lengths beyond the 3m–12m range, we review rolling feasibility and provide a lead-time estimate before you place the order.
Q: What is the difference between black, pre-galvanized, and hot-dip galvanized finishes?
A: Black (oiled) tubes are the most economical choice for indoor structures where final painting occurs on-site. Pre-galvanized tubes carry a 40–80g/m² zinc coating suitable for fencing, greenhouse frames, and light outdoor use. Hot-dip galvanized tubes at 200–600g/m² provide long-term corrosion protection for highway railings, coastal solar structures, and applications where maintenance access is limited.
Q: How do you handle CE certification and EU customs compliance?
A: Our carbon steel square and rectangular tubes carry CE marking under EN 10210 and EN 10219, supported by a Factory Production Control (FPC) certificate and a Declaration of Performance. These documents are included in every EU-bound shipment to prevent customs holds.
Get Your Carbon Steel Square Pipe Tube Quote Today
Email your dimensions, steel grade, and quantity to admin@sdxinjiyuan.com or message +86 188 5315 7756 on WhatsApp to receive a factory-direct quotation with mill test certificate samples.
