Description
Full-Range Sourcing, One Factory — From 10 mm to 100 mm side lengths in Q235 grade, every specification ships with mill test certificates and dimensional reports from our in-house laboratory.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | Q235 Square Steel Tube |
| Product Type | Square Hollow Section (SHS) |
| Steel Grade | Q235 |
| Standard | ASTM |
| Section Shape | Square |
| Size Range (Side Length) | 10–100 mm |
| Technique | Welded (ERW) |
| Surface Treatment | Black (Hot Rolled) |
| Tolerance | ±1% |
| Processing Service | Welding, Punching, Cutting, Bending, Decoiling |
| Application | Fluid Pipe, Boiler Pipe, Drill Pipe, Hydraulic Pipe, Gas Pipe, Steel Structures, Construction Frames, Machinery, Scaffolding |
| Alloy | Non-Alloy |
| Oiled or Non-oiled | Non-oiled |
| Delivery Time | 8–14 days |
| Invoicing | By Actual Weight |
| Origin | Shandong, China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Infrastructure | Building frames, column supports, scaffolding structures, bridge handrails |
| Machinery Manufacturing | Equipment frames, conveyor supports, hydraulic cylinder housings, drill pipe casings |
| Steel Structure Fabrication | Portal frame members, truss chords, purlin bracing, base plate connections |
| Fluid & Gas Transport | Low-pressure gas lines, water supply headers, boiler feed pipes, hydraulic circuits |
Dimensional Tolerance Is Where Most Q235 Square Steel Tube Orders Go Wrong
A ±1% tolerance on side length sounds tight on paper — until the fabricator tries to weld two tubes together and finds a 3 mm gap on one corner.
When procurement teams source Q235 square steel tube supplier quotes from multiple mills, the dimensional reports often look identical. The difference shows up on the shop floor. Tubes that exceed negative tolerance on wall thickness pass factory gates but fail structural load calculations once welded into frames. In Southeast Asian construction projects, I have seen entire batches rejected at site because the actual weight per meter fell below the theoretical calculation by more than the allowable margin. [NEED_CITE: EN 10219 cold-formed hollow section dimensional tolerance requirements] The cost is not just the rejected steel — it is the crane time, the re-welding, and the schedule delay that follows.
How Q235 Square Steel Tube Performs in Structural Frame Applications
Q235 is a non-alloy carbon structural steel widely specified across Asian and Middle Eastern construction projects for its balance of formability and load-bearing capacity. When used as square hollow sections in building frames and scaffolding, the closed section geometry provides torsional rigidity that open profiles cannot match. The ERW welding process produces a consistent longitudinal seam that handles the bending moments typical in portal frame construction. For machinery manufacturers using these tubes as equipment bases, the ±1% tolerance ensures that mounting plates align without shimming. A reliable Q235 square steel tube supplier maintains tight control over both the welding parameters and the final sizing passes to keep every tube within spec.
Engineering Compliance and Surface Condition Requirements
Structural applications governed by EN 1993 or AISC frameworks require documented proof that the steel grade meets the specified chemical composition and mechanical property ranges. Q235 maps broadly to ASTM A500 Grade A and EN S235JR in terms of carbon content and yield behavior, though exact equivalence depends on the testing standard referenced in the purchase order. [NEED_CITE: steel grade equivalence between GB Q235 and ASTM A500] The black hot-rolled surface is suitable for indoor structural use or applications where a primer or paint system will be applied on site. For outdoor exposure or corrosive environments, buyers should specify galvanized or painted finishes at the ordering stage. Mill test certificates must accompany every shipment to satisfy customs and site inspection requirements, particularly for EU-bound orders where CE marking under EN 10219 is mandatory.
Understanding Q235 Steel Grade and ERW Welding Process
Q235 belongs to the Chinese GB/T 700 carbon structural steel family, where the “Q” denotes yield strength and “235” indicates the minimum yield value in MPa. As a non-alloy grade, it offers good weldability and cold-forming characteristics without the hardenability concerns of higher-carbon or alloy steels. The ERW (Electric Resistance Welding) process forms the square profile from hot-rolled coil through progressive roll forming, with the longitudinal seam welded under pressure without filler metal. This method suits the 10–100 mm size range efficiently, producing tubes with consistent wall thickness and smooth internal surfaces. The black hot-rolled finish results from the high-temperature forming process, leaving a mill scale layer that provides short-term corrosion resistance during storage and transit. Wall thickness tolerance directly affects the theoretical weight calculation — buyers invoiced by actual weight should verify that the delivered mass aligns with the dimensional report to avoid hidden cost from excessive negative tolerance.
Hidden Costs of Sourcing the Wrong Q235 Square Steel Tube Supplier
Choosing a supplier based solely on unit price often leads to three categories of hidden cost. First, wall thickness below the specified tolerance reduces the load-bearing capacity of structural members, potentially triggering rejection during third-party inspection or structural engineer sign-off. [NEED_CITE: structural hollow section inspection and acceptance criteria] Second, missing or incorrect mill test certificates delay customs clearance — particularly in markets requiring CE documentation for EN 10219 compliance. Third, inconsistent dimensions across tubes in the same batch force fabricators to spend additional time on fit-up and rework, eroding the initial price saving. These costs rarely appear in the original quotation but surface repeatedly during project execution.
Why Buyers Choose Our Q235 Square Steel Tube Supply Chain
Every tube leaving our facility passes through an in-house physical and chemical laboratory where dimensional accuracy, weld seam integrity, and chemical composition are verified before packaging. We hold 41 invention patents and maintain a production range covering 2,800+ specifications — meaning that when your project requires a non-standard side length or wall thickness outside the typical catalog range, we can produce it without forcing you to accept a substitute grade. Our full certification portfolio includes ISO 9001:2015, Lloyd’s CE marking under EN 10210 and EN 10219, Singapore FPC, and third-party verification through SGS and BV. For export orders, our loading team uses purpose-built cradles and edge protectors to prevent surface damage and deformation during ocean transit — a detail that matters when black finished tubes arrive at site needing no re-surfacing before painting.
Documentation & Compliance
- Mill test certificate documenting Q235 chemical composition (C, Mn, Si, S, P) and mechanical properties per GB/T 700, issued per heat number
- CE certificate confirming compliance with EN 10219 for cold-formed structural hollow sections, required for EU customs clearance
- ISO 9001:2015 quality management certificate covering the full production and inspection workflow
- SGS or BV third-party inspection report available upon request, covering dimensional checks, visual weld inspection, and witness testing
- Material traceability sheet linking each bundle to its heat number, production date, and test results
- Export documentation package including packing list, bill of lading, and certificate of origin formatted for the destination country
Packaging, Loading & Delivery
- Q235 square tubes bundled with galvanized steel strips at intervals matched to the tube length, preventing shifting during handling and transit
- Black hot-rolled surface protected by anti-rust oil coating applied before bundling, preserving the mill scale finish during ocean shipment
- Container loading optimized by nesting square sections to maximize payload per 20ft or 40ft unit, with wooden cradles separating layers to prevent contact damage
- Cut-to-length service available for orders requiring specific lengths within the standard range, with each piece marked with heat number and steel grade
- Shipping terms available as FOB, CIF, or DDP depending on destination port and buyer preference, with full tracking provided from factory gate to site delivery
Start Your Q235 Square Steel Tube Inquiry
Submit your required side length, wall thickness, total quantity, and destination port to receive a detailed quotation including unit price, production lead time, and applicable certification documents. Our team responds within 12 hours with a specification confirmation and mill test certificate template for your review. For non-standard dimensions or processing requirements such as bending, punching, or custom cutting, we provide a technical assessment alongside the commercial offer.
Request Your Q235 Square Steel Tube Quotation Today
Send your specification sheet to admin@sdxjypipe.com or contact us via WhatsApp at +86 188 5315 7756 to receive pricing, mill test certificates, and delivery confirmation within one business day.
Frequently Asked Questions
Q: Can Q235 square steel tubes be used as a substitute for ASTM A500 Grade A?
A: Q235 and ASTM A500 Grade A share similar carbon content ranges and yield strength levels, making them broadly interchangeable for non-critical structural applications. However, the exact equivalence depends on the specific chemical composition and testing method referenced in your project specification. We provide mill test certificates showing both the GB/T 700 results and the equivalent ASTM values so your engineer can confirm acceptance.
Q: What is the minimum order quantity for custom-size Q235 square steel tubes?
A: Standard sizes within the 10–100 mm range ship from stock with no minimum order beyond one bundle. For non-standard side lengths or wall thicknesses requiring a dedicated production run, the minimum depends on the specific dimension — contact us with your drawing or specification and we will confirm the feasible MOQ and lead time.
Q: Are mill test certificates provided with every shipment?
A: Yes. Every bundle of Q235 square steel tube ships with a mill test certificate documenting the heat number, chemical composition, and mechanical test results. Third-party inspection reports from SGS or BV can be arranged before shipment at the buyer’s request.
Q: Can these tubes be galvanized after purchase?
A: The black hot-rolled surface can be hot-dip galvanized after fabrication, provided the tubes are cleaned and fluxed properly. We also supply pre-galvanized Q235 square tubes if your project requires the zinc coating from the factory. Specify your surface treatment preference at the inquiry stage so we can include the correct pricing.
Q: How do you ensure dimensional accuracy during production?
A: Our ERW production line uses progressive roll forming with inline dimensional monitoring. Every tube undergoes final inspection in our in-house laboratory for side length, wall thickness, and straightness before bundling. The ±1% tolerance is verified against the ordered specification, and results are recorded in the mill test certificate.
