Description
Factory-direct ERW square and rectangular steel tube supply — Q235B and Q345B grades manufactured on dedicated ERW lines with wall thickness up to 50mm, shipped with original mill test certificates to 50+ countries.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235B ERW Square and Rectangular Steel Tube |
| Product Type | Welded Square and Rectangular Steel Tube (ERW) |
| Steel Grade | Q195, Q235, Q235B, Q345, Q345B, SS400, A53, A106, S235JR, S275JR, S355J2 |
| Standard | ASTM A53, ASTM A106, API 5L, EN Standard, GB Standard, JIS |
| Section Shape | Square / Rectangular |
| Size Range | 15mm × 15mm – 800mm × 800mm |
| Wall Thickness | 1mm – 50mm |
| Length | 6m / 12m or Customized |
| Technique | ERW (Electric Resistance Welded), Hot Rolled, Cold Rolled |
| Surface Treatment | Black Painted, Varnished, Galvanized (Hot-Dip / Electro), 3LPE/3LPP Coated, Oiled |
| Tolerance | ±1% |
| Ends | Plain / Beveled |
| Application | Construction, Oil & Gas, Automotive, Machinery, Shipbuilding |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| EPC Contractors | Structural frameworks for industrial plants, scaffolding systems, equipment support structures |
| Construction Companies | High-rise building columns, bridge support members, infrastructure foundation piles |
| Machinery Manufacturers | Hydraulic cylinder housings, pneumatic system frames, conveyor support structures |
| Oil & Gas | Pipeline transmission conduits, drilling platform support members, process pipe racks |
| Shipbuilding | Marine piping systems, offshore platform structural members, deck support frameworks |
What Wall-Thickness Tolerance Costs on a Structural Frame Order
Tolerance deviation beyond ±1% on an ERW square and rectangular steel tube order can trigger rejections at third-party inspection and delay entire project timelines.
When procurement teams receive hollow sections with inconsistent wall thickness, the structural engineer cannot verify load-bearing calculations against design specifications. [NEED_CITE: EN 10219 cold-formed structural hollow section tolerance requirements] Thin-wall sections fail ultrasonic thickness testing at site, forcing partial replacement orders that arrive weeks behind schedule. Meanwhile, over-thick sections add unplanned dead load to the structure and inflate transport costs per container. The root cause often traces back to suppliers who lack in-house dimensional control during the ERW forming and welding process.
Matching ERW Hollow Sections to Structural Load Requirements
An ERW square and rectangular steel tube in Q235B or Q345B grade serves as primary load-bearing members in portal frame structures and mezzanine platforms. The electric resistance welding process produces a continuous longitudinal seam that, when controlled within ±1% wall thickness tolerance, delivers consistent section modulus across the full 15mm × 15mm to 800mm × 800mm size range. For projects requiring corrosion resistance in coastal or industrial environments, hot-dip galvanized surface treatment extends service life without additional field coating. Our proprietary sharp-corner rectangular tube technology ensures flat bearing surfaces at connection points, eliminating gaps that compromise bolted or welded joints in structural frames.
Engineering Compliance and Certification Requirements
Structural hollow sections used in load-bearing applications must conform to recognized standards — EN 10210/10219 for European markets, ASTM A500 for North American projects, and GB/T 6728 for domestic Chinese construction. [NEED_CITE: structural steel certification requirements for EU customs clearance] The Q235B and Q345B grades in this ERW square and rectangular steel tube line meet GB standard chemical composition and mechanical property requirements, while S235JR through S355J2 grades conform to EN specifications for European project compliance. Lloyd’s Register EU CE certification under EN 10210/10219 enables direct customs clearance across member states, and Singapore FPC certification supports Southeast Asian infrastructure procurement. Third-party inspection by SGS or BV is available for every shipment, with original mill test certificates documenting heat number traceability from slab to finished tube.
Steel Grade Selection and ERW Process Fundamentals
The Q-series carbon structural steels (Q195 through Q345B) follow the Chinese GB standard system, where the number indicates minimum yield strength in MPa. Q235B delivers adequate strength for general structural frameworks and scaffolding, while Q345B provides higher load capacity for heavy-duty industrial structures and bridge components. The S-series (S235JR, S275JR, S355J2) follows the European EN standard with equivalent or superior mechanical properties, and the J suffix denotes guaranteed impact toughness at sub-zero temperatures — critical for cold-climate installations. [NEED_CITE: steel grade equivalence between GB, EN, and ASTM standards]
The ERW manufacturing process forms flat steel strip into square or rectangular cross-sections through continuous cold forming, then welds the longitudinal seam using high-frequency electric resistance. This method produces tight dimensional tolerances and smooth surface finish compared to seamless or SSAW alternatives, making ERW tubes ideal for architectural applications and precision machinery frames. Wall thickness from 1mm to 50mm covers light-gauge decorative sections through heavy structural members, with the ±1% tolerance maintained through in-process dimensional monitoring at each forming stand.
Surface treatment selection depends on the service environment: black painted or oiled finish suits indoor structural applications with controlled humidity; hot-dip galvanizing provides 65μm+ zinc coating for outdoor exposure and coastal corrosion resistance; 3LPE/3LPP coating systems offer maximum protection for buried or submerged pipeline applications.
Hidden Costs of Non-Conforming Hollow Section Procurement
Purchasing ERW square and rectangular steel tube from suppliers without verified quality control creates compounding project risks. Material that fails to meet declared steel grade specifications will not pass structural engineer approval at site, requiring costly replacement and schedule recovery. [NEED_CITE: consequences of non-conforming structural steel in construction projects] Missing or incomplete mill test certificates cause customs delays at destination ports, particularly in EU markets where CE certification under EN 10210/10219 is mandatory. Negative tolerance abuse — where actual wall thickness falls below the minimum specified — reduces load-bearing capacity and creates safety liability for the structural engineer and building owner. These hidden costs far exceed the initial price difference between certified and uncertified suppliers.
Procurement Confidence Through Verified Manufacturing Capability
Factory-direct pricing on every ERW square and rectangular steel tube order eliminates trading company markups, with transparent cost breakdowns showing material, processing, and logistics components separately. Our in-house physical and chemical laboratory conducts incoming raw material inspection, in-process dimensional checks during ERW forming, and final mechanical property testing before shipment — every heat number is traceable from steel coil to finished tube. The product range covers 2,800+ specifications across square, rectangular, and round sections, enabling single-source procurement for mixed-specification project orders that would otherwise require coordination across multiple suppliers. Proprietary sharp-corner rectangular tube technology — protected by 41 invention patents — delivers true 90-degree internal corners that standard ERW forming cannot achieve, providing flat bearing surfaces for precision structural connections. Lloyd’s Register EU CE certification, ISO 9001:2015 quality management, Singapore FPC, and SGS/BV third-party verification ensure compliance across 50+ export destinations. Professional container loading optimization maximizes payload per shipment while protecting surface treatment integrity during ocean transit.
Documentation & Compliance
- Mill test certificate documenting Q235B chemical composition (C, Si, Mn, P, S content) and mechanical properties (yield strength, tensile strength, elongation) per GB/T 700 standard
- Lloyd’s Register EU CE certificate confirming EN 10210/10219 compliance for S235JR and S355J2 grades destined for European construction projects
- ISO 9001:2015 quality management system certificate covering the full ERW square and rectangular steel tube manufacturing process from raw material incoming inspection to final shipment
- SGS or BV third-party inspection report verifying dimensional tolerance, surface treatment thickness, and visual quality for project-specific quality assurance requirements
- Material traceability documentation linking each tube bundle to its heat number, enabling full chain-of-custody verification from steel coil to installed structural member
- Customs clearance package including commercial invoice, packing list, bill of lading, and certificate of origin formatted for destination country import requirements
Packaging, Loading & Delivery
- ERW square and rectangular steel tube bundles secured with minimum four steel straps per bundle, with edge protectors preventing damage to galvanized coating or painted finish during handling and transit
- Hot-dip galvanized tubes wrapped in waterproof plastic sheeting within each bundle to prevent white rust formation from condensation during ocean container shipping
- Container loading plans optimized for 6m and 12m standard lengths, with nested smaller sections (15mm × 15mm through 100mm × 100mm) filling void spaces between larger rectangular tubes to maximize payload per 20ft or 40ft container
- Custom cut-to-length service available for Q235B and Q345B grades, with saw-cut ends deburred and protected against corrosion for immediate site installation
- Each bundle tagged with heat number, steel grade (Q235B/Q345B/S355J2), section dimensions, wall thickness, and length for positive identification at project site
- FOB, CIF, and DDP shipping terms available with professional logistics coordination for port-to-port or door-to-door delivery to construction sites across 50+ countries
Initiating Your ERW Hollow Section Procurement
Submit your project specifications including section dimensions, wall thickness, steel grade, quantity, surface treatment preference, and destination port to receive a detailed quotation with unit pricing, production lead time, and applicable certification documentation. Our technical team reviews each inquiry within 12 hours and provides mill test certificate samples for quality verification before contract signing. For non-standard dimensions outside the 15mm × 15mm to 800mm × 800mm range or custom surface treatment requirements, we provide feasibility assessment and pricing for specialized production runs.
Request Quotation with Mill Test Certificate
Send your ERW square and rectangular steel tube specifications via email to admin@sdxjysteel.com or contact our international sales team at +86 188 5315 7756 (WhatsApp/WeChat available) for pricing and certification documentation within 12 hours.
Frequently Asked Questions
Q: What is the difference between Q235B, S235JR, and ASTM A53 steel grades for structural applications?
A: Q235B follows the Chinese GB standard with minimum 235 MPa yield strength, S235JR conforms to European EN 10025 with equivalent yield strength and guaranteed room-temperature impact energy, and ASTM A53 covers seamless and welded pipe for mechanical and pressure applications. All three grades are available in our ERW square and rectangular steel tube product line, with grade selection depending on project specification requirements and destination market standards.
Q: Can you provide third-party inspection and original mill test certificates for customs clearance?
A: Yes, every shipment includes original mill test certificates documenting chemical composition and mechanical properties per the declared steel grade standard. Third-party inspection by SGS or BV is available upon request for dimensional verification, surface treatment thickness measurement, and visual quality assessment. Lloyd’s Register EU CE certification under EN 10210/10219 supports customs clearance across European Union member states.
Q: What surface treatment options are available for corrosion protection in different environments?
A: Our ERW square and rectangular steel tube product line offers black painted finish for indoor applications, oiled surface for temporary rust prevention during transit, hot-dip galvanized coating with minimum 65μm zinc thickness for outdoor and coastal exposure, electro-galvanized finish for lighter corrosion protection requirements, and 3LPE/3LPP coating systems for buried or submerged pipeline applications. Surface treatment selection depends on your project’s environmental conditions and design service life requirements.
Q: What is the minimum order quantity for custom non-standard dimensions?
A: Standard sizes within our 15mm × 15mm to 800mm × 800mm range with 1mm to 50mm wall thickness are available from stock with typical production lead times. Custom non-standard dimensions outside this range require minimum order quantity assessment based on production setup requirements — please submit your specifications for feasibility evaluation and pricing.
Q: How do you handle container optimization for mixed-specification orders?
A: Our logistics team develops container loading plans that maximize payload by nesting smaller square and rectangular sections within larger tubes and filling void spaces with compatible dimensions. For mixed orders combining Q235B, Q345B, and galvanized products, we coordinate production sequencing to enable consolidated shipment with proper surface protection for each treatment type. FOB, CIF, and DDP terms are available with professional port coordination and real-time tracking.
