Description
Direct Mill Supply for Precision ERW Tubes — Q235B and Q345B welded square rectangular steel tube produced on our own ERW lines with ±1% dimensional tolerance and full mill test certification.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B / Q345B Welded Square and Rectangular Steel Tube |
| Product Type | Welded Square and Rectangular Steel Tube (ERW) |
| Steel Grade | Q195, Q215, Q235, Q345B, S235JR, S355JR, SS400 |
| Standard | ASTM, DIN EN 10217-1, JIS, ISO 9001 |
| Section Shape | Square, Rectangular, Round |
| Size Range | 30×30mm, 30×40mm, 50×50mm (custom sizes available) |
| Wall Thickness | 1mm–3mm |
| Length | 6m, 6.4m, 12m (custom lengths available) |
| Technique | ERW (Cold Rolled / Hot Rolled) |
| Surface Treatment | Hot Rolled, Oiled / Non-oiled |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Construction building material, steel structures, machinery manufacturing, fluid transport, scaffolding, furniture manufacturing, architectural decoration |
| MOQ | 5 Tons |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building frames, scaffolding systems, bridge support structures |
| Architectural Decoration | Curtain wall framing, visible structural elements, furniture manufacturing |
| Machinery Manufacturing | Equipment frames, conveyor structures, industrial component supports |
| Steel Structures | Warehouse portals, mezzanine floors, purlin and bracing systems |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
A ±1% tolerance on a 2mm wall Q235B welded square rectangular steel tube means the difference between passing third-party inspection and returning an entire container for rework.
I have seen projects where standard rectangular tubes with rounded corners and inconsistent wall thickness caused fit-up failures on construction sites. Facade contractors using these tubes for glass curtain wall framing found that cumulative tolerance errors across multiple joints created visible misalignment. The Q235B and Q345B welded square rectangular steel tube we produce maintains strict dimensional control through cold rolled ERW processing, ensuring that 30×30mm and 50×50mm sections arrive with consistent load-bearing capacity. When wall thickness varies beyond acceptable limits, structural engineers cannot verify compliance with EN 10219 cold-formed hollow section requirements [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerances].
Matching Thin-Wall ERW Tubes to Light Structural Applications
The 1mm–3mm wall thickness range of this Q235B Q345B welded square rectangular steel tube targets applications where weight reduction matters without sacrificing structural integrity. Scaffolding systems benefit from the lighter gauge while maintaining the rigidity needed for worker safety. Furniture manufacturers and architectural decorators specify these tubes because the hot rolled surface finish accepts powder coating directly without extensive preparation. The ERW cold rolled process produces a smooth flat surface that works for visible structural elements in commercial interiors.
Engineering Compliance and Certification Requirements
Structural applications require documentation proving the steel grade meets specified standards. Our Q235B and Q345B tubes conform to GB standards, while S235JR and S355JR grades meet EN 10219 requirements for European projects. The steel grade equivalence between Chinese GB and European EN standards often causes ordering confusion [NEED_CITE: steel grade equivalence between EN and ASTM standards]. For North American projects, we supply to ASTM A500 specifications. Third-party inspection through SGS or BV confirms dimensional accuracy and material properties before shipment, preventing customs clearance delays at destination ports.
Understanding ERW Welding Process and Grade Selection
ERW (Electric Resistance Welding) forms the tube by rolling steel strip into shape and welding the seam through electrical resistance heating. This process suits thin-wall applications from 1mm to 3mm where seamless tubes would be cost-prohibitive. The Q series (Q195, Q235, Q345B) represents Chinese standard designations where the number indicates minimum yield strength in MPa. S235JR and S355JR follow European EN standards with similar yield strength progression. For architectural decoration, the hot rolled surface treatment provides adequate corrosion resistance for indoor applications, while oiled surface protects against rust during ocean transit.
Hidden Costs of Incorrect Grade Specification and Tolerance Violations
Specifying Q235B when the design requires Q345B creates structural safety risks that only surface during load testing. Conversely, over-specifying to Q345B when Q235B suffices inflates material costs unnecessarily. Negative tolerance exceeding contractual limits triggers rejection during third-party inspection, forcing return shipments or on-site rework that delays project timelines. Missing mill test certificates or incorrect CE marking blocks EU customs clearance, leaving containers stranded at port while documentation issues resolve [NEED_CITE: CE marking requirements for structural steel imports to EU].
Why Source This Q235B Q345B Welded Square Rectangular Steel Tube From Us
We operate three dedicated ERW production lines covering over 2,800 specifications, eliminating the specification gaps that force buyers to source from multiple suppliers. Our in-house physical and chemical laboratory performs dimensional verification and material testing on every production batch, generating mill test certificates before shipment. The ±1% tolerance control comes from cold rolled ERW processing rather than hot rolled methods that struggle with thin-wall consistency. We hold ISO 9001:2015 certification, Lloyd’s CE marking for EN 10210 and EN 10219 standards, and Singapore FPC approval for regulated market projects. Professional container loading with anti-damage measures prevents the bending and surface scratches that cause rejection at destination.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition and mechanical properties per GB/T 700 standard
- CE certificate confirming EN 10219 compliance for S235JR and S355JR structural hollow sections
- ISO 9001:2015 quality management system certificate covering ERW tube production processes
- SGS or BV third-party inspection report verifying dimensional tolerance and surface quality before shipment
- Material traceability by heat number linking each bundle to specific steel coil and production batch
- Complete customs documentation including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- Q235B and Q345B tubes bundled with steel strips in seaworthy packaging, with edge protectors preventing surface damage to hot rolled finish during ocean transit
- Oiled surface treatment applied to non-galvanized tubes to prevent rust formation during extended shipping periods to Middle East and South America destinations
- Container loading optimized for 6m and 12m lengths, maximizing payload while preventing tube movement and bending during transit
- Custom cutting to specified lengths available, reducing on-site fabrication waste for scaffolding and furniture manufacturing applications
- Heat number and steel grade identification marked on each bundle end, enabling quick verification during site receiving inspection
- FOB, CIF, and DDP shipping terms available with professional export documentation and tracking until arrival at destination port
Requesting Quotation and Technical Documentation for Your Project
Submit your specification requirements including section dimensions, wall thickness, steel grade, surface treatment preference, quantity, and destination port to receive detailed quotation within 12 hours. We provide mill test certificates, third-party inspection options, and custom non-standard size confirmation before production begins. Our technical team reviews your application requirements to verify grade selection and tolerance specifications match your engineering standards.
Frequently Asked Questions
Q: What is the difference between Q235B and S235JR steel grade for this welded square rectangular steel tube?
A: Both grades offer similar yield strength around 235 MPa, but Q235B follows Chinese GB/T 700 standard while S235JR conforms to European EN 10025 standard. For projects requiring CE marking and EU customs clearance, specify S235JR. For domestic Chinese projects or regions accepting GB standards, Q235B provides equivalent performance at lower cost.
Q: Can you produce non-standard sizes outside the 30×30mm to 50×50mm range listed?
A: Yes, we manufacture custom non-standard sizes beyond the standard range. Our three production lines cover over 2,800 specifications. Submit your required dimensions and we confirm feasibility, minimum order quantity, and production lead time. Custom sizes typically require 15–25 days production time compared to standard sizes shipping from stock.
Q: What surface treatment options are available for architectural decoration applications?
A: Standard surface treatment includes hot rolled finish (suitable for powder coating), oiled surface (rust prevention during transit), and non-oiled (for immediate fabrication). For outdoor architectural applications requiring corrosion resistance, we offer hot dip galvanizing as an additional processing service. The smooth flat surface from our ERW cold rolled process accepts direct coating without extensive surface preparation.
Q: How do you ensure dimensional tolerance meets ±1% requirement for thin-wall tubes?
A: Our ERW cold rolled production process maintains tighter dimensional control than hot rolled methods. In-house laboratory performs dimensional verification on every production batch using calibrated measurement equipment. Mill test certificates document actual measurements. Third-party inspection through SGS or BV available upon request to verify tolerance compliance before shipment.
Q: What documentation do you provide for EU customs clearance?
A: We provide CE certificate confirming EN 10219 compliance for S235JR and S355JR grades, mill test certificates per EN 10204 3.1 format, and complete customs documentation including packing list, bill of lading, and certificate of origin. Lloyd’s CE marking covers EN 10210 and EN 10219 standards required for structural steel imports to European Union member states.
Get Your Q235B Q345B Welded Square Rectangular Steel Tube Quote Today
Send your specification requirements to receive detailed pricing, mill test certificate samples, and production lead time confirmation.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxjypipe.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjypipe.com
