Description
Full-Range Square & Rectangular Tube Supply — Vertically integrated mill and fabrication facility covering Q195 through Q345 grades in side lengths from 100×100 mm to 500×500 mm, delivering complete material traceability from raw steel to finished section.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235 Square Steel Tube |
| Product Type | Square and Rectangular Welded Steel Tube |
| Steel Grade | Q195, Q235, Q345 |
| Standard | ASTM, JIS, DIN |
| Section Shape | Square / Rectangular |
| Size Range | 100×100 mm – 500×500 mm |
| Wall Thickness | 0.5 – 30 mm |
| Length | 6 – 12 m |
| Technique | Hot Rolled / Cold Rolled (Welded) |
| Surface Treatment | Hot Rolled, Oiled / Non-oiled |
| Tolerance | ±1% |
| Ends | Plain |
| Application | Steel structures / Construction frames / Building material / Bridges / Machinery / Scaffolding |
| MOQ | 5 Tons |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Commercial Construction | Building frames, column systems, roof trusses for warehouses and logistics centers |
| Industrial Infrastructure | Platform structures, pipe rack supports, equipment foundations in petrochemical plants |
| Civil Engineering | Bridge handrails, scaffolding systems, temporary support frames |
| Machinery Manufacturing | Conveyor frames, crane booms, agricultural equipment structural members |
What Negative Tolerance Deviation Costs on a Square Tube Order
Dimensional accuracy on wall thickness directly determines whether a shipment clears third-party inspection or sits at port for weeks.
Procurement teams sourcing Q235 square steel tube from fragmented supply chains frequently encounter wall thickness readings that drift beyond the acceptable negative tolerance band. When a third-party surveyor pulls random samples at the discharge port and finds readings outside the ±1% envelope, the entire container gets held pending re-inspection or return authorization. The cost is never just the steel — it is crane idle time, missed erection windows, and the contractual penalties that follow. [NEED_CITE: dimensional tolerance requirements for cold-formed structural hollow sections]
Matching Section Geometry to Structural Frame Demands
A Q235 square steel tube in the 200×200 to 300×300 mm range with wall thickness between 6 mm and 12 mm serves as the primary load-bearing member in portal frame warehouses and industrial shed structures. The flat internal surfaces of square sections simplify bolted end-plate connections and allow direct bearing against gusset plates without additional machining. For scaffolding and temporary works, the 100×100 mm to 150×150 mm range with lighter wall gauges provides adequate load capacity while keeping handling weight manageable on site. Our fabrication division produces these sections in-house from our own mill output, meaning the chemical composition recorded on the mill test certificate traces directly back to the heat of steel that formed the tube — no third-party sourcing gaps.
Engineering Compliance and Certification Pathways
Structural engineers specifying Q235 square steel tube for load-bearing frames in international projects must verify compliance with the governing code — ASTM A500 for North American projects, EN 10219 for European work, and JIS G3466 for Japanese-specification contracts. The Q235 grade maps broadly to S235JR under EN standards and ASTM A500 Grade B in terms of minimum yield strength, but formal equivalence requires documented chemical composition and mechanical test results rather than assumption. [NEED_CITE: steel grade equivalence mapping between Chinese GB standards and ASTM/EN systems] Surface condition matters for corrosion planning: hot-rolled oiled tubes suit indoor structural applications where painting or fireproofing will follow, while non-oiled surfaces require immediate downstream treatment to prevent transit oxidation. Third-party inspection bodies such as SGS, BV, and TÜV verify dimensional compliance and surface quality before shipment, and the full documentation package travels with the cargo for customs and site acceptance.
Understanding the Q-Grade Steel System and Welded Tube Production
The Q-series designation follows the Chinese GB/T 700 standard, where the number after “Q” indicates the minimum yield strength in MPa — Q195 yields at approximately 195 MPa, Q235 at 235 MPa, and Q345 at 345 MPa. For general structural framing where loads remain moderate, Q235 offers the best balance of formability, weldability, and cost. When projects demand higher load capacity in smaller section sizes, stepping up to Q345 reduces the required wall thickness and therefore the self-weight of the structure. The welded manufacturing process for these square and rectangular tubes involves forming flat strip into the target section geometry and applying a continuous longitudinal weld seam. Hot-rolled production suits heavier wall thicknesses above 6 mm where forming forces are higher, while cold-rolled processing achieves tighter dimensional tolerances on thinner-walled sections. The ±1% tolerance specification applies across the full 0.5 mm to 30 mm wall thickness range, and our in-line ultrasonic testing verifies weld integrity on every running length. [NEED_CITE: welded versus seamless hollow section manufacturing process comparison]
Hidden Costs When Material Certification Falls Short
Ordering Q235 square steel tube without verified mill test certificates creates risk that surfaces only at the inspection stage. Tubes produced from unconfirmed heat numbers may carry chemistry outside the specified carbon equivalent range, compromising weldability and creating crack sensitivity in field connections. When negative tolerance on wall thickness exceeds the stated ±1% limit, the theoretical weight calculation diverges from actual delivered weight — and the structural engineer’s load assumptions no longer match what was erected. Projects governed by EN 1090 execution standards require full traceability from heat to finished member, and missing documentation means the entire batch fails acceptance regardless of physical quality. [NEED_CITE: EN 1090 structural steel fabrication certification and traceability requirements]
Procurement Confidence Through Integrated Production
Our facility operates three dedicated production lines for square and rectangular welded tubes, backed by our own steel mill producing over 2,800 specifications of raw material. This vertical integration means the Q235 square steel tube you order comes from a single quality system — the same chemistry verified at the ladle stage carries through forming, welding, and final inspection. We hold ISO 9001:2015 certification verified by TÜV, and our welding procedures comply with AWS and EN standards with qualified welders on staff. For projects requiring CE marking under EN 10219, we provide the full Factory Production Control documentation package. Our engineering team reviews shop drawings before production begins, identifying potential fabrication sequencing issues that would otherwise generate costly RFIs during erection.
Documentation & Compliance
- Mill Test Certificate documenting Q235 chemical composition (C, Mn, Si, S, P) and yield strength per ASTM / GB standards, traceable to specific heat number
- Third-party inspection report from SGS, BV, or TÜV covering dimensional verification, visual weld inspection, and surface condition assessment
- ISO 9001:2015 quality management certificate demonstrating certified production processes and documented quality control procedures
- Material traceability sheet linking each bundle to its heat number, production date, and test sample identification
- Complete customs documentation package including commercial invoice, packing list, bill of lading, and certificate of origin
- Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR) available for projects requiring verified weld integrity
Packaging, Loading & Delivery
- Q235 square steel tubes bundled with high-tensile steel strips at intervals calculated for the specific section size, preventing shift during ocean transit
- Hot-rolled oiled surfaces receive edge protectors and interlayer separation to preserve the oil film and prevent contact corrosion between stacked members
- Container loading plans optimized for 6 m and 12 m lengths, maximizing payload within the 5-ton MOQ while respecting weight distribution limits for 20-foot and 40-foot units
- Plain-end tubes receive capped or wrapped end protection to prevent damage to the weld seam and edge condition during handling
- Each bundle marked with heat number, steel grade (Q195/Q235/Q345), section dimensions, and length for immediate site identification
- Shipment terms available as FOB, CIF, or DDP with professional oversized cargo loading coordination for project-specific delivery requirements
Initiating Your Procurement Inquiry
Submit your project drawings in PDF or DWG format along with the required steel grade, section dimensions, wall thickness, total quantity, and destination port. Our engineering team responds within 24 hours with a preliminary assessment covering material availability, production scheduling, and preliminary pricing. For non-standard dimensions outside the 100×100 mm to 500×500 mm range, we provide custom fabrication feasibility review and lead time confirmation before contract commitment.
Request Your Q235 Square Tube Quotation
Share your specifications and receive detailed pricing with full mill test certification documentation within one business day.
Company: Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.xjystructure.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@xjystructure.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
Frequently Asked Questions
Q: How does Q235 grade compare to ASTM A500 Grade B for structural applications?
A: Q235 and ASTM A500 Grade B share similar minimum yield strength characteristics, making them broadly interchangeable for general structural framing. However, formal project acceptance requires documented chemical composition and mechanical test results rather than assumption of equivalence. We provide mill test certificates that allow your engineer to verify compliance with the governing specification for your project.
Q: What third-party inspection options are available before shipment?
A: We coordinate inspections through SGS, Bureau Veritas, and TÜV covering dimensional verification, visual weld examination, surface condition assessment, and witness testing. The inspection scope and acceptance criteria are confirmed against your project specification before the survey date is scheduled, and the full report is included in the shipping documentation package.
Q: Can you produce non-standard dimensions outside the listed size range?
A: Our fabrication division handles custom section sizes based on engineering drawings. Submit your required dimensions, wall thickness, and quantity for a feasibility assessment covering production method, lead time, and minimum order requirements for non-standard sections.
Q: What surface treatment options are available for corrosion protection?
A: We supply hot-rolled tubes in oiled condition for indoor structural applications where painting or fireproofing follows, and non-oiled condition for projects requiring immediate galvanizing or coating application. Galvanizing and painting services are coordinated through our finishing partners based on your project specification and environmental exposure requirements.
Q: How is theoretical weight calculated versus actual delivered weight?
A: Theoretical weight is calculated from the nominal section dimensions and wall thickness using standard steel density. Actual delivered weight is measured on calibrated scales at the time of loading. Our ±1% tolerance specification applies to dimensional measurements, and we document both theoretical and actual weights on the packing list for your records.
