Description
Factory-Direct Welded Carbon Steel Square Tube — Full-range Q195–Q355 / S235JR–S355JR welded square and rectangular hollow sections produced on dedicated lines with in-house laboratory testing, shipped without middlemen markup.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Customized Sizes Welded Carbon Steel Square/Rectangular Pipe |
| Product Type | Welded Carbon Steel Square and Rectangular Tube (SHS/RHS) |
| Steel Grade | Q195, Q235, Q355 (S235JR, S355JR), ASTM A53 Grade A/B, ASTM A500 Grade A/B/C, JIS SS400, STK400, ST42.2 |
| 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 | 1.2mm–20mm |
| Length | 3m–12m (random or customized) |
| Technique | Welded (Hot Rolled Hollow Carbon Pipe) |
| Surface Treatment | Pre-galvanized (40–80g/m²) / Hot-dipped galvanized (200–600g/m²) / Custom requirement |
| Tolerance | ±1% |
| Ends | Plain / Customized |
| Application | Construction, steel structures, solar structures, fence posts, greenhouse frames, machinery, shipbuilding, power engineering, highway railings, bridges |
| MOQ | 1 Ton |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC Contractors & Construction | Steel structure frames for warehouses, building columns and beams, bridge support components |
| Infrastructure & New Energy | Solar farm mounting structures, greenhouse skeleton frames, highway guardrail posts |
| Machinery & Industrial | Equipment base frames, conveyor support structures, power engineering brackets |
| Fencing & Agriculture | Perimeter fence posts, greenhouse purlins, agricultural shed frameworks |
What Wall-Thickness Tolerance Costs on a Customized Sizes Welded Carbon Steel Square Pipe Order
A ±1% tolerance on a 20mm wall means the difference between passing structural inspection and scrapping an entire shipment at port.
When a Middle East EPC contractor ordered a batch of custom-size welded carbon steel square tubes for a solar mounting project, the wall thickness negative tolerance exceeded the EN10219 limit. The third-party inspector flagged the entire container. Cargo sat at the port for weeks while re-inspection was arranged, and the project timeline slipped by a month. That kind of delay does not come from the steel itself — it comes from unchecked tolerance at the mill. [NEED_CITE: EN 10219 cold-formed hollow section requirements]
Matching Customized Sizes Welded Carbon Steel Square Pipe to Structural Frame Requirements
Engineers specifying welded carbon steel square tubes for structural frames need to verify that section geometry, wall thickness, and steel grade align with load calculations under EN 1993 or AISC standards. The 20×20mm to 500×500mm size range with wall thickness from 1.2mm to 20mm covers everything from light-duty fence posts to heavy-load-bearing columns. For projects combining square and rectangular sections in one structure, sourcing a Customized Sizes Welded Carbon Steel Square Pipe supplier who holds 2,800+ specifications in stock eliminates the coordination risk of ordering from multiple mills.
Engineering Compliance and Certification Pathways
Structural hollow sections destined for EU markets must conform to EN10219 for cold-formed welded products or EN10210 for hot-finished equivalents, with CE marking under the Construction Products Regulation. North American projects typically require ASTM A500 Grade B or C compliance. Steel grade equivalence between EN (S235JR/S355JR), GB (Q235/Q355), and ASTM (A53/A500) systems must be documented clearly to avoid customs holds. [NEED_CITE: steel grade equivalence between EN and ASTM standards] Third-party inspection by SGS or BV before shipment provides independent verification that chemical composition and dimensional tolerances meet the specified standard, which is often a contractual prerequisite for EPC projects.
Steel Grade Selection and Welded Process Fundamentals
The Q-series (Q195, Q235, Q355) and S-series (S235JR, S355JR) designations represent increasing yield strength levels — Q355/S355JR delivers higher load-bearing capacity than Q235/S235JR, making it the preferred choice for primary structural members. ASTM A500 Grade B and C serve similar roles in North American specifications, with Grade C offering the highest strength among the three grades. The welded (ERW) process forms the tube from hot-rolled coil through continuous forming and longitudinal seam welding, producing consistent wall thickness and tight dimensional tolerance across long production runs. Surface treatment selection depends on the service environment: pre-galvanized coating at 40–80g/m² suits indoor or lightly corrosive conditions, while hot-dipped galvanizing at 200–600g/m² provides long-term protection for outdoor exposure, coastal installations, and industrial atmospheres. [NEED_CITE: hot-dip galvanizing coating thickness for structural steel]
Hidden Costs of Procuring the Wrong Grade or Missing Certification
Ordering Q235 when the structural drawing specifies S355JR means the delivered tubes cannot carry the design load — the entire batch becomes scrap or requires costly downgrading to non-structural use. Missing CE certification on an EN10219 order triggers customs rejection at EU ports, regardless of whether the steel itself is perfectly sound. Negative tolerance exceeding the ±1% contractual limit means the actual weight falls below the theoretical calculation, creating a discrepancy that inspectors flag immediately. [NEED_CITE: EN 10219 dimensional tolerance requirements for structural hollow sections] These are not theoretical risks — they are routine failure points on international steel procurement projects where documentation and tolerance control are treated as afterthoughts.
Procurement Confidence Through Verified Factory Capability
Every Customized Sizes Welded Carbon Steel Square Pipe order ships with original mill test certificates generated by our in-house physical and chemical laboratory, covering chemical composition, tensile strength, and dimensional inspection results. Our dedicated production lines cover 2,800+ specifications including non-standard dimensions, with custom sizes available at a 1-ton MOQ for trial orders. We hold Lloyd’s Register EU CE certification under EN10210 and EN10219, ISO 9001:2015 quality management certification, and Singapore FPC approval — all verified by SGS and BV. Our proprietary sharp-corner rectangular tube technology, backed by 41 patents, fills a gap that standard catalog products cannot address. Professional container loading plans optimize weight distribution for 3m–12m lengths, and our logistics team coordinates FOB, CIF, and DDP shipments to 50+ countries.
Documentation & Compliance
- Mill test certificate documenting Q235/Q355 chemical composition and mechanical properties per GB/T 6728 and EN10219, with heat number traceability
- CE certificate under EN10210 and EN10219 for EU market customs clearance and construction project compliance
- ISO 9001:2015 quality management system certificate covering production and inspection processes
- SGS or BV third-party inspection report available upon request for independent dimensional and material verification
- Full customs document package including packing list, bill of lading, and certificate of origin for destination port clearance
Packaging, Loading & Delivery
- Welded carbon steel square tubes bundled with steel strips and edge protectors to prevent coating damage during handling and ocean transit
- Pre-galvanized and hot-dipped galvanized surfaces wrapped with waterproof paper and plastic sleeves to preserve zinc coating integrity
- Container loading plans optimized for 3m–12m lengths across 20ft and 40ft containers, maximizing weight utilization for 20×20mm to 500×500mm sections
- Custom cut-to-length service available for 1.2mm–20mm wall thickness tubes, with plain or beveled ends per project requirement
- Heat number and steel grade marked on each tube bundle for on-site material identification and traceability verification
- FOB, CIF, and DDP shipping terms available with door-to-door logistics coordination to 50+ countries
Start Your Welded Carbon Steel Square Pipe Inquiry
Submit your specification sheet including section dimensions, wall thickness, steel grade, quantity, and destination port to receive a detailed quotation with mill test certificate preview and estimated production timeline. Our engineering team reviews custom non-standard size requests within 12 hours and provides technical recommendations on steel grade equivalence and surface treatment selection for your project environment.
Get Your Customized Sizes Welded Carbon Steel Square Pipe Quote
Send your specifications via email or WhatsApp to receive pricing, certification documents, and delivery schedule within 12 hours.
Company: Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxjysteel.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjysteel.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
Frequently Asked Questions
Q: How do Q235/Q355 grades map to S235JR/S355JR and ASTM A500 for my project specification?
A: Q235 corresponds to S235JR under EN10219, and Q355 corresponds to S355JR. For ASTM systems, Q235 is broadly equivalent to ASTM A500 Grade A, while Q355 aligns with ASTM A500 Grade B. We provide a full steel grade equivalence table with every quotation to ensure your procurement matches the structural drawing requirements.
Q: Can you provide EN 10204 3.2 certificates and arrange SGS/BV third-party inspection?
A: Yes. We issue EN 10204 3.1 mill test certificates as standard with every shipment, documenting chemical composition and mechanical properties by heat number. EN 10204 3.2 certificates with third-party witness are available upon request, and we coordinate SGS or BV inspection at our facility before shipment at the buyer’s option.
Q: What is the minimum order quantity for custom dimensions outside your standard catalog?
A: The MOQ for custom non-standard sizes is 1 ton. Our production lines cover 2,800+ specifications including side lengths from 20×20mm to 500×500mm and wall thickness from 1.2mm to 20mm. Custom lengths up to 12m and non-standard rectangular proportions are available with typical production lead times confirmed at quotation stage.
Q: When should I specify pre-galvanized versus hot-dipped galvanized surface treatment?
A: Pre-galvanized coating at 40–80g/m² is suitable for indoor structural applications, light corrosion environments, and projects where appearance uniformity is prioritized. Hot-dipped galvanized coating at 200–600g/m² is recommended for outdoor exposure, coastal installations, solar farm structures, and industrial atmospheres where long-term corrosion resistance is critical.
Q: Do your CE and EN certifications cover EU market import and project compliance requirements?
A: Yes. Our Lloyd’s Register EU CE certification covers both EN10210 and EN10219 standards, which satisfies the Construction Products Regulation for structural steel hollow sections entering EU markets. We also hold Singapore FPC certification for Southeast Asian projects and provide full customs documentation including certificate of origin for destination port clearance.
