Description
Factory-Direct Seamless Hollow Sections — Hot-rolled Q195 to Q345 square and rectangular tubes produced in-house with full EN10219 and ASTM A500 certification, shipped without trading margins.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Carbon Seamless Square Steel Tube |
| Product Type | Seamless Square and Rectangular Hollow Section |
| Steel Grade | Q195, Q215, Q235, Q345, 20#, 45# |
| Standard | EN10219, EN10210, GB/T 6728, JIS G3466, ASTM A500, ASTM A36 |
| Section Shape | Square, Rectangular, Round |
| Size Range | Square 20×20 mm – 500×500 mm; Rectangular 20×40 mm – 300×500 mm |
| Wall Thickness | 1.2 mm – 20 mm |
| Length | 3 m – 12 m (random) |
| Technique | Seamless (Hot Rolled) |
| Surface Treatment | Black / Pre-galvanized (40–80 g/m²) / Hot-dipped galvanized (200–600 g/m²) |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures, construction frames, machinery, solar structures, glass curtain walls, scaffolding, furniture, greenhouse frames |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Commercial Construction | Building frames, glass curtain wall mullions, architectural facade supports |
| Industrial Infrastructure | Solar mounting structures, conveyor frames, equipment platforms |
| Machinery Manufacturing | Precision machine bases, hydraulic support columns, roller frames |
| Agricultural Engineering | Greenhouse skeleton frames, irrigation pipe supports, livestock shelter structures |
| General Fabrication | Scaffolding uprights, furniture frames, fencing posts |
What Dimensional Tolerance Costs on a Seamless Carbon Square Steel Tube Order
±1% tolerance on hot-rolled seamless sections means the difference between a frame that bolts together on-site and one that needs field rework.
When procurement teams order a Seamless Carbon Square Steel Tube for structural frames, the first failure point is rarely the steel grade — it is the tolerance stack-up across dozens of members. A wall thickness that drifts beyond ±1% changes the moment of inertia, shifts bolt-hole alignment, and forces fabricators to shim or re-cut on the job site. We have seen entire curtain wall sub-frames rejected at destination because the cumulative tolerance error across 200 pieces exceeded the engineer’s 3 mm allowance. The Seamless Carbon Square Steel Tube we ship carries mill-tested dimensional reports so your site team can weld and bolt without second-guessing each member [NEED_CITE: EN 10219 cold-formed and hot-rolled hollow section dimensional tolerance requirements].
Matching Seamless Hollow Sections to Structural and Corrosive Environments
Hot-rolled seamless square and rectangular sections carry load through uniform wall geometry without a weld seam, making them the default choice for columns and moment frames where eccentric loading is expected. For a Seamless Carbon Square Steel Tube in Q345 or 20# grade, the absence of a longitudinal weld means the full cross-section yields uniformly under compression — critical for solar racking columns in high-wind zones and machinery bases under cyclic vibration. When the same tube moves into a greenhouse or coastal facade environment, the hot-dipped galvanized option at 200–600 g/m² zinc coating extends service life without field painting. Our production lines cover side lengths from 20 mm to 500 mm with wall thickness up to 20 mm, so a single purchase order can frame an entire warehouse from column to purlin without splitting suppliers.
Engineering Compliance and Certification Pathways
Structural engineers specifying hollow sections for EU projects require CE marking under EN 10210 or EN 10219 — without it, customs holds the container at the port of entry regardless of material quality [NEED_CITE: CE marking requirements for structural steel hollow sections under EN 10210]. For North American projects, ASTM A500 Grade B or C compliance governs acceptance, and the grade equivalence between Q345 and S355JR or ASTM A500 Gr.C must be documented on the mill test certificate, not assumed from purchase orders. Our in-house physical and chemical laboratory tests every heat for composition, yield behavior, and dimensional accuracy before release. Random lengths of 3 m to 12 m can be cut to exact erection lengths at the mill, reducing on-site waste and eliminating the need for field torch-cutting that compromises galvanized coatings.
Steel Grade Selection and Hot-Rolled Seamless Process Logic
The Q-series grades — Q195 through Q345 — follow the Chinese yield-strength naming convention where the number approximates minimum yield strength in MPa. Q195 and Q215 serve light structural and furniture applications where formability matters more than load capacity. Q235 is the workhorse grade for general construction frames, equivalent in intent to S235JR under EN standards and ASTM A36 in the US system. Q345 steps into heavy structural territory, mapping to S355JR and ASTM A500 Gr.C for columns and beams carrying higher axial loads. The 20# and 45# grades are carbon-manganese steels selected for machined connections and precision mechanical components where surface hardness and tensile uniformity take priority over weldability. Hot-rolled seamless production eliminates the weld seam entirely — the tube is pierced from a solid billet and elongated over a mandrel, producing a homogeneous cross-section with consistent mechanical properties around the full perimeter. This matters for pressure-containing applications and for structural members where torsional loading could expose a weld-line weakness. Surface treatment selection follows the environment: black finish for interior or painted structures, pre-galvanized at 40–80 g/m² for moderate humidity, and hot-dipped galvanized at 200–600 g/m² for outdoor exposure or corrosive atmospheres.
Hidden Costs of Unverified Tube Procurement
Ordering a Seamless Carbon Square Steel Tube without verified mill test certificates shifts risk from the supplier to the buyer’s balance sheet. A tube stamped Q345 that tests as Q235 in an independent lab does not just fail inspection — it forces the entire batch to be re-ordered, delaying erection schedules and triggering liquidated damages on the main contract [NEED_CITE: structural steel material verification requirements under EN 10204 inspection document types]. Missing CE documentation blocks EU customs clearance, stranding containers at the port for weeks while the importer scrambles for retroactive certification. Negative tolerance abuse — where wall thickness consistently drifts below the nominal minus the allowed deviation — reduces load capacity silently, passing visual inspection but failing structural calculations under peer review. The cost of rework, delay, and reputational damage far exceeds the per-ton price difference between a verified mill and an unverified trader.
Why Procurement Teams Source Seamless Hollow Sections from SD XJY Pipe
We operate three production lines covering over 2,800 specifications, so a single inquiry for square, rectangular, and round sections in mixed grades returns one consolidated quote rather than fragmented supplier responses. Our in-house laboratory performs dimensional, mechanical, and chemical testing on every heat before release — the mill test certificate you receive reflects actual test data, not template values copied from a standard. We hold CE certification under EN 10210 and EN 10219, ISO 9001:2015 registration, and Singapore FPC approval, with SGS and BV third-party inspection available before loading. Custom non-standard sizes and cut-to-length service mean your erection drawings drive the mill schedule, not the other way around. Professional container loading with anti-damage measures prevents the bending and surface scratches that trigger rejection at destination — a lesson we learned the hard way on an early export order that came back from the Middle East. We export to over 50 countries and serve as a designated supplier for major state-owned enterprises and listed companies, which means our documentation and traceability systems meet the audit requirements of the most demanding project owners.
Documentation & Compliance
- Mill test certificate documenting Q195–Q345 chemical composition and mechanical properties per EN 10219 and ASTM A500, issued per heat number
- CE certificate covering EN 10210 and EN 10219 for structural hollow sections exported to EU member states
- ISO 9001:2015 quality management system certificate covering seamless tube and section steel production
- SGS or BV third-party inspection report available upon request, covering dimensional verification and coating thickness measurement for galvanized finishes
- Material traceability by heat number from billet receipt through final shipment, supporting project-specific documentation packages
- Full customs documentation including packing list, bill of lading, and certificate of origin formatted for destination-country clearance
Packaging, Loading & Delivery
- Seamless square and rectangular tubes bundled with high-tensile steel strips, separated by timber dunnage to prevent surface contact damage during ocean transit
- Hot-dipped galvanized tubes (200–600 g/m²) wrapped with edge protectors and waterproof paper to preserve zinc coating integrity through loading and unloading
- Container loading optimized for 3 m to 12 m random lengths, with heavier wall thickness sections (up to 20 mm) positioned at the base to distribute weight and prevent shifting
- Cut-to-length service available for Q235 and Q345 grades, with saw-cut ends deburred and marked by heat number and steel grade for on-site identification
- Shipping terms FOB, CIF, or DDP with full export documentation and tracking until arrival at destination port or project site
Starting Your Seamless Carbon Square Steel Tube Inquiry
Send your specification sheet covering section dimensions, steel grade, surface treatment, quantity, and destination port — we return a detailed quotation with unit pricing, production lead time, and available mill test certificate formats within 12 hours. For non-standard sizes outside the 20×20 mm to 500×500 mm range, share your drawing and we confirm feasibility and tooling requirements. Certification and customs documentation needs should be stated upfront so we align the production batch with your destination market requirements.
Frequently Asked Questions
Q: How do Q235 and Q345 grades map to EN and ASTM equivalents?
A: Q235 corresponds in intent to S235JR under EN 10219 and ASTM A36 in the US system. Q345 maps to S355JR under EN standards and ASTM A500 Grade C. Full chemical composition and mechanical property equivalence is documented on the mill test certificate for each heat [NEED_CITE: steel grade equivalence between GB, EN, and ASTM standards].
Q: Can you provide third-party inspection before shipment?
A: Yes. SGS and BV inspection reports covering dimensional verification, coating thickness measurement for galvanized finishes, and mechanical testing are arranged on request. The inspection is conducted at our facility before container loading.
Q: What is the MOQ for custom non-standard sizes?
A: The standard MOQ is 1 Ton. For custom non-standard dimensions outside the 20×20 mm to 500×500 mm range or wall thickness beyond 20 mm, we confirm feasibility and minimum tonnage based on your specific drawing.
Q: What surface treatment options are available for outdoor applications?
A: Three options are available: black finish for interior or painted structures, pre-galvanized at 40–80 g/m² for moderate humidity environments, and hot-dipped galvanized at 200–600 g/m² for outdoor exposure or corrosive atmospheres including coastal and industrial zones.
Q: Do your products carry CE certification for EU market entry?
A: Yes. We hold CE certification under EN 10210 and EN 10219 for structural hollow sections. The CE mark and Declaration of Performance are included in the shipment documentation package for EU customs clearance [NEED_CITE: CE marking and Declaration of Performance requirements for structural steel products].
Request Your Seamless Carbon Square Steel Tube Quotation
Submit your section dimensions, steel grade, surface treatment, and quantity to receive a detailed quotation with mill test certificate confirmation 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
Website: www.sdxjypipe.com
