Description
Direct Mill Supply for Q235 Q345 Carbon Steel Seamless Square Tube — 20×20–600×600 mm hot-rolled seamless hollow sections with wall thickness up to 500 mm, produced and tested in-house for heavy structural and pressure applications.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235/Q345 Carbon Steel Seamless Square Pipe |
| Product Type | Seamless Square Steel Pipe |
| Steel Grade | Q195, Q235, Q235B, Q275, Q345, Q345B, Q420, Q460, S235JR, S275JR, S355JR, SS400, SS330, ST37-2, ST52, STK490, ASTM A36, A53, A106 |
| Standard | ASTM A36, A53, A106, EN 10210, EN 10219, DIN 17100, JIS G3466, GB |
| Section Shape | Square |
| Size Range | 20×20 – 600×600 mm |
| Wall Thickness | 30 – 500 mm |
| Length | 1 – 12 m (standard 6 m) |
| Technique | Seamless / Hot Rolled |
| Surface Treatment | Oiled, Bare, Black Paint, Galvanized |
| Tolerance | ±1% |
| Ends | Plain End |
| Alloy | Non-Alloy |
| Application | Civil engineering, architecture, steel structures, steel towers, shipyard, scaffolding, fluid pipe, boiler pipe, hydraulic pipe, gas pipe, oil pipe, chemical fertilizer pipe, structure pipe |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Civil Engineering & Infrastructure | Bridge piers, foundation piles, transmission tower legs, heavy scaffolding uprights |
| Architecture & Steel Structures | Building column frames, industrial workshop frames, stadium roof trusses |
| Shipyard & Marine | Deck stanchions, hull stiffeners, ballast system piping |
| Fluid & Pressure Systems | Boiler tubes, hydraulic cylinder barrels, gas transmission lines, oil field casing |
| Industrial Machinery | Conveyor support frames, crane boom sections, hydraulic press columns |
Why Heavy-Wall Seamless Square Tubes Fail at Customs Without EN 10210 Documentation
Missing CE marking or incorrect EN standard references on mill test certificates block EU imports — regardless of physical quality.
Procurement teams ordering Q235 Q345 carbon steel seamless square tube for European projects often discover the problem only at destination port. The tubes pass visual inspection, but customs brokers flag the shipment because the mill test certificate references GB standards instead of EN 10210 or EN 10219, or the CE declaration is absent entirely. In Southeast Asia, I have seen 40-foot containers held for weeks while importers scrambled to obtain retroactive third-party inspection reports from SGS or BV. The root cause is not the steel itself — it is the documentation gap between the mill’s domestic certification and the destination market’s regulatory requirements. [NEED_CITE: EN 10210 hot-finished structural hollow section certification requirements for EU customs]
Matching Seamless Square Tubes to High-Load Structural and Pressure Applications
Q235 Q345 carbon steel seamless square tube in 600×600 mm with 500 mm wall thickness serves load-bearing columns in high-rise construction and hydraulic press frames where welded alternatives cannot withstand the internal pressure or point loads. The hot-rolled seamless process eliminates the weld seam — the typical failure point under cyclic loading — and delivers uniform grain structure across the entire cross-section. For shipyard stanchions and boiler tubes, the seamless wall resists internal corrosion and external buckling simultaneously. Our in-house laboratory tests every heat number for chemical composition and mechanical properties before release, so the mill test certificate matches the physical shipment.
Engineering Compliance: EN 10210, ASTM A36, and JIS G3466 Across Markets
Structural designers specifying Q235 Q345 carbon steel seamless square tube must confirm compliance with the destination country’s code: EN 10210 for European projects, ASTM A36 or A53 for North American work, JIS G3466 for Japanese-specification industrial plants. The steel grade equivalents — Q235B to S235JR to ASTM A36 — share similar yield strength ranges, but the testing methods, impact energy requirements, and tolerance classes differ. [NEED_CITE: steel grade equivalence mapping between GB Q series and EN S series for structural hollow sections] For pressure applications such as boiler pipe or hydraulic pipe, ASTM A106 adds elevated-temperature tensile requirements that Q235 alone does not satisfy. Our technical team cross-references your project specification against the mill’s production standard before contract signing, preventing grade substitution disputes at site inspection.
Steel Grade Selection: Q235 vs Q345 vs S355JR for Structural Load Paths
Q235 provides adequate strength for non-critical framing and scaffolding, while Q345 (equivalent to S355JR under EN 10219) delivers higher yield strength for primary load-bearing columns and crane booms. The Q-series follows Chinese GB standards; the S-series follows European EN standards; ASTM A36/A53 follows American standards. Selecting the wrong grade — for example, specifying Q235 when the structural engineer calculated for S355JR — forces on-site reinforcement or full replacement. For heavy-wall seamless square tube above 100 mm thickness, Q345 or Q460 is typically required to prevent internal voids during hot-rolling. [NEED_CITE: hot-rolled seamless square tube manufacturing process and wall thickness limitations] Surface treatment selection depends on the service environment: galvanized finish for outdoor exposure and marine splash zones, oiled or black painted for indoor structural use where welding will follow, bare for applications requiring field-applied coating systems.
The Hidden Cost of Negative Tolerance and Unverified Mill Test Certificates
Ordering Q235 Q345 carbon steel seamless square tube based on theoretical weight without confirming actual wall thickness leads to structural under-design. A 30 mm nominal wall delivered at 27 mm — a 10% negative tolerance — reduces the section modulus and load capacity below the engineer’s calculation. Third-party inspection at destination reveals the discrepancy, but the tubes are already cut and welded. The cost is not the steel price difference; it is the demolition, re-fabrication, and project delay. [NEED_CITE: dimensional tolerance requirements for structural hollow sections per EN 10210] Similarly, mill test certificates fabricated by trading companies — not backed by actual heat-number traceability — fail auditor review and void project insurance coverage.
Procurement Confidence: In-House Testing, Full Certification, and Direct Mill Access
We produce Q235 Q345 carbon steel seamless square tube on our own hot-rolling lines, not through brokered inventory from unknown sources. Every batch undergoes chemical analysis, tensile testing, and dimensional measurement in our physical and chemical laboratory before shipment. Our 2,800+ specification range covers the full 20×20 to 600×600 mm size and 30–500 mm wall thickness scope — including non-standard dimensions that most mills reject. We hold ISO 9001:2015, Lloyd’s CE certification for EN 10210 and EN 10219, Singapore FPC, and accept SGS or BV third-party inspection at your request. For export orders, our loading team uses dedicated cradles and edge protectors to prevent surface damage and ovality during ocean transit — a detail that matters when 500 mm wall tubes arrive bent.
Documentation & Compliance
- Mill Test Certificate (EN 10204 3.1) documenting Q235/Q345 chemical composition, yield strength, tensile strength, and elongation per GB/T 1591 or EN 10210 as specified
- CE Certificate (EN 10210 / EN 10219) issued by Lloyd’s Register for European market customs clearance and structural compliance
- ISO 9001:2015 Quality Management System certificate covering seamless square tube production, testing, and dispatch
- SGS or BV Third-Party Inspection Report verifying dimensional tolerance, surface quality, and wall thickness before container sealing
- Material Traceability Report linking each tube bundle to heat number, chemical analysis, and mechanical test results
- Export Documentation including commercial invoice, packing list, bill of lading, and certificate of origin for destination customs
Packaging, Loading & Delivery
- Heavy-wall seamless square tubes (30–500 mm thickness) bundled with high-tensile steel strips and separated by timber dunnage to prevent surface scratching during transit
- Galvanized finish tubes wrapped with waterproof paper and edge protectors to preserve zinc coating integrity during ocean freight
- 6 m and 12 m standard lengths loaded in 20-foot and 40-foot open-top containers with custom steel cradles to prevent ovality and bending
- Custom cut-to-length service available for 1–12 m requirements, with cut ends deburred and protected against corrosion
- Heat number and steel grade (Q235/Q345) stenciled on each tube bundle for site identification and traceability
- FOB, CIF, and DDP shipping terms available from Qingdao port to destination ports across 50+ countries
Submit Specifications for Mill Test Certificate and Pricing
Provide your required size (20×20 to 600×600 mm), wall thickness (30–500 mm), steel grade (Q235, Q345, or equivalent), surface treatment, quantity, and destination port. We respond within 12 hours with unit pricing, production lead time, and a sample mill test certificate for your engineer’s review. Non-standard dimensions and custom lengths are available with low MOQ.
Request Your Q235 Q345 Carbon Steel Seamless Square Tube Quote
Send your specifications to receive pricing, mill test certificate preview, and third-party inspection arrangement details.
Contact: 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
Frequently Asked Questions
Q: How do Q235 and Q345 steel grades map to ASTM A36/A500 and EN S235JR/S355JR equivalents?
A: Q235B corresponds to S235JR (EN 10219) and ASTM A36 in yield strength range; Q345B corresponds to S355JR and ASTM A500 Grade B/C. The chemical composition and testing methods differ slightly across standards, so we provide cross-reference documentation with every mill test certificate to confirm compliance with your project specification.
Q: Can you provide SGS or BV third-party inspection before shipment?
A: Yes. We arrange SGS or BV inspection at our facility or at the loading port upon request. The inspection covers dimensional tolerance, wall thickness measurement, surface quality, and visual examination. The inspection report is issued before container sealing and accompanies the shipment documentation.
Q: What is the minimum order quantity for non-standard sizes outside your 2,800+ specification range?
A: We accept custom non-standard dimensions with low MOQ, typically 1 ton for standard grades and 5 tons for special grades or heavy-wall sections. Lead time for custom production is 15–25 days depending on size and quantity. Standard sizes within our existing specification range ship from stock.
Q: When should I specify galvanized finish versus oiled or black painted surface treatment?
A: Galvanized finish is recommended for outdoor exposure, marine environments, or applications where long-term corrosion resistance is critical. Oiled or black painted finish is suitable for indoor structural use where the tubes will be welded or coated on-site. Bare finish is specified when the project requires field-applied coating systems such as epoxy or polyurethane.
Q: How are heavy-wall seamless square tubes packed to prevent damage during ocean freight?
A: Tubes are bundled with high-tensile steel strips, separated by timber dunnage, and loaded in containers with custom steel cradles to prevent ovality and bending. Galvanized tubes receive additional waterproof wrapping and edge protectors. Our loading team has professional experience with heavy-wall sections up to 500 mm thickness and ensures secure stowage for long-distance ocean transit.
