Description
Direct Mill Supply — Every Q195-Q345 seamless square tube verified in-house before loading
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Steel Seamless Square Steel Pipe |
| Product Type | Seamless Square and Rectangular Hollow Section |
| Steel Grade | Q195, Q235, Q345, 10#, 20# |
| Standard | GB/T 6728, EN 10210, EN 10219, JIS G3466, BS, ASTM A106, ASTM A335, ASTM A213, JIS G3458, DIN 17175, GB 5310, GB 9948 |
| Section Shape | Square / Rectangular |
| Side Length | 20mm–610mm |
| Wall Thickness | 0.6mm–20mm |
| Technique | Seamless (Hot Rolled) |
| Surface Treatment | Bare / Varnish Painting / Galvanized / Custom painting |
| Tolerance | ±1% / ±5% |
| Ends | Plain |
| Application | Civil engineering / Architecture / Steel towers / Shipyard / Scaffolding / Structural frames |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Civil Engineering & Infrastructure | Bridge support columns, foundation piling sleeves, tunnel reinforcement frames |
| Architecture & Facade | Glass curtain wall mullions, exposed structural columns, canopy framing |
| Steel Towers & Transmission | Lattice tower leg members, antenna mast base sections |
| Shipyard & Marine | Deck stanchions, cargo hold framing, pipeline support racks |
| Scaffolding & Temporary Works | Load-bearing vertical standards, ledger transoms, shoring towers |
| Industrial Structural Frames | Equipment support platforms, conveyor gantry columns, mezzanine bracing |
What Wall-Thickness Tolerance Costs on a Seamless Square Steel Tube Order
A few hundred microns of negative tolerance can void an entire shipment at third-party inspection.
I have seen full containers of rectangular hollow sections rejected at destination because wall thickness measured below the minimum allowed by EN 10219 — not by much, just enough for the inspector’s caliper to flag every piece. The steel looked fine, the welds were clean, but the paperwork could not save the cargo. Hot rolled seamless square and rectangular tubes in Q235 or Q345 demand tighter process control than welded alternatives, because there is no weld seam to compensate for uneven wall distribution. When your Seamless Square Steel Tube order crosses borders, the mill test certificate must match what the caliper reads on the dock. [NEED_CITE: EN 10219 cold-formed hollow section tolerance requirements]
Matching Structural Load Paths in Tower and Scaffold Applications
Hot rolled seamless square tubes in the 20mm–610mm side-length range carry compressive and bending loads more predictably than welded sections of equivalent weight, because the seamless forming process produces a more uniform grain structure around the entire perimeter. For steel tower leg members and scaffolding standards, this uniformity translates directly into reliable buckling resistance — the calculation inputs match the physical reality. Our production lines cover over 2,800 specification combinations, so a project engineer specifying Q345 seamless square tube at 150×150×8mm does not need to accept the nearest “available” size and recalculate.
Engineering Code Compliance and Surface Protection Selection
Structural frames designed to EN 1993 or AISC 360 require hollow sections that conform to recognized dimensional and material standards — EN 10210 for hot-finished or GB/T 6728 for Chinese-spec projects. [NEED_CITE: steel grade equivalence between GB Q-series and EN S-series standards] For outdoor towers and shipyard applications, the choice between bare, varnish painted, or galvanized surface treatment depends on the corrosion environment: galvanized coating suits marine splash zones, while varnish painting offers cost-effective protection for indoor structural frames. CE certification under EN 10210/10219 is mandatory for EU-bound shipments, and our Lloyd’s CE mark covers the full Q195–Q345 range. Custom non-standard lengths and cut-to-size services reduce on-site welding and secondary processing at the erection stage.
Decoding Q195–Q345 Grades and Hot Rolled Seamless Process
The Q-series carbon steel grades — Q195, Q235, Q345 — follow the Chinese GB system where the number indicates minimum yield strength in MPa. Q195 serves light structural and non-load-bearing framing; Q235 is the workhorse grade for general construction and scaffolding; Q345 delivers higher yield strength for heavy structural frames, tower legs, and bridge components. The 10# and 20# grades, designated by carbon content, are selected for machining and pressure applications where weldability and ductility take priority over raw strength. Hot rolled seamless production eliminates the weld seam entirely, producing a homogeneous cross-section that handles multi-directional loading without the heat-affected zone weaknesses inherent in ERW or SSAW alternatives. [NEED_CITE: seamless versus welded hollow section performance under cyclic loading] Wall thickness from 0.6mm to 20mm covers everything from lightweight architectural mullions to heavy-duty industrial columns, and the ±1% / ±5% tolerance bands align with both EN 10219 and GB/T 6728 requirements.
Hidden Costs When Material Certification Does Not Match the Caliper
Ordering Seamless Square Steel Tube without verified mill test certificates creates a chain of risk: customs authorities in regulated markets demand CE documentation traceable to heat numbers, and a missing or mismatched certificate halts clearance. [NEED_CITE: EU customs documentation requirements for structural steel imports] Negative tolerance beyond the standard band does not just reduce theoretical weight — it reduces the actual section modulus, meaning the tube cannot carry the load the structural engineer calculated for. Rework at the erection stage, replacement shipments, and project delay penalties dwarf any per-ton savings from uncertified supply.
Why Project Procurement Teams Specify Our Mill Directly
Every Seamless Square Steel Tube leaving our facility passes through our in-house physical and chemical laboratory — dimensional checks with calibrated micrometers, tensile testing, and spectrographic composition analysis per heat number. We hold 41 invention patents, including China’s original sharp-corner rectangular tube technology, which means our production capability extends well beyond standard radiused sections into true right-angle profiles for architectural facades. Full international certification — ISO 9001:2015, Lloyd’s CE under EN 10210/10219, Singapore FPC, and SGS/BV third-party verification — covers exports to over 50 countries. Our 3 production lines span 2,800+ specifications with wall thickness up to 20mm, so custom non-standard sizes carry low minimum order quantities. Professional container loading with anti-deformation bracing has eliminated transit damage claims across our export shipments.
Documentation & Compliance
- Mill test certificate documenting Q195, Q235, or Q345 chemical composition and mechanical properties per GB/T 6728 or EN 10210, traceable by heat number
- CE certificate issued under EN 10210 (hot-finished) and EN 10219 (cold-formed) for EU market customs clearance
- ISO 9001:2015 quality management system certificate covering the full seamless square and rectangular hollow section range
- SGS or BV third-party inspection report available upon request, covering dimensional, mechanical, and visual examination
- Material traceability report linking each bundle to its heat number, chemical analysis, and tensile test results
- Full customs documentation package: packing list, bill of lading, certificate of origin, and commercial invoice
Packaging, Loading & Delivery
- Bare or varnish-painted Q235 and Q345 seamless square tubes bundled with high-tensile steel strips, separated by timber dunnage to prevent surface scratching during ocean transit
- Galvanized seamless square tubes packed with edge protectors and waterproof wrapping to preserve the zinc coating layer through humidity exposure
- 20ft and 40ft container loading plans optimized for 20mm–610mm side-length tubes, with internal steel bracing frames to prevent shifting and deformation under vessel motion
- Cut-to-length service available for plain-end tubes, with lengths marked per bundle and heat number stenciled on each piece for on-site traceability
- Shipping terms FOB, CIF, or DDP to ports across Southeast Asia, the Middle East, EU, and North America, with full tracking until destination arrival
Securing Your Seamless Square Steel Tube Quotation
Submit your dimension schedule — side length, wall thickness, steel grade, surface treatment, quantity, and destination port — and receive a detailed quotation within 12 hours, including unit pricing, production lead time, and shipping terms. For non-standard sizes outside the 20mm–610mm range, our engineering team provides custom feasibility confirmation and tooling timelines. All quotations include mill test certificate scope and third-party inspection options so your procurement file is complete before contract signing.
Frequently Asked Questions
Q: Can you supply seamless square tubes to EN 10210 or EN 10219 standards for EU projects?
A: Yes. Our Lloyd’s CE certification covers both EN 10210 (hot-finished) and EN 10219 (cold-formed) hollow sections, and we provide full CE documentation with every EU-bound shipment.
Q: What is the minimum order quantity for custom non-standard sizes?
A: We offer low MOQ for custom non-standard dimensions across our 2,800+ specification range. Contact us with your exact size requirements for a specific MOQ confirmation.
Q: Do you provide third-party inspection before shipment?
A: Yes. SGS and BV third-party inspections are available on request, covering dimensional verification, mechanical testing, and visual examination before container sealing.
Q: How do Q235 and Q345 grades compare to international equivalents?
A: Q235 broadly corresponds to S235JR under EN standards and ASTM A36, while Q345 aligns with S355JR/J2 and ASTM A572 Grade 50. We provide grade equivalence documentation with every order to support your engineering specifications.
Q: What surface treatment options are available for seamless square tubes?
A: We offer bare (mill finish), varnish painting, hot-dip galvanized, and custom painting to match your project’s corrosion protection requirements.
Get Your Seamless Square Steel Tube Quote with Full Certification Package
Send your specification sheet — dimensions, steel grade, surface treatment, quantity, and destination — to receive a detailed quotation and mill test certificate scope within 12 hours.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjypipe.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
