Advanced Manufacturing Process,The Modern Structural Solution
The Square Hollow Tube (SHS) is a fundamental structural steel section characterized by its hollow, square-shaped cross-section. It offers an exceptional balance of strength, weight, and aesthetics, making it indispensable for construction, manufacturing, and architectural projects. The final properties and suitability of the tube are significantly defined by two key finishing processes: galvanizing and black annealing.
High Strength-to-Weight Ratio: The hollow design provides excellent structural rigidity and load-bearing capacity using less steel than a solid bar, reducing material and transportation costs.
Uniform & Aesthetic Shape: The clean, flat faces and sharp 90-degree corners of an SHS make it highly desirable for visible architectural and furniture applications.
Weldable & Machinable: SHS can be easily cut, drilled, and welded using standard equipment, offering high versatility in fabrication.
Understanding the two primary finishes is critical for specification.
Galvanized Square Hollow Tube:
Process: The fabricated tube is cleaned and then immersed in a bath of molten zinc (typically around 450°C), creating a durable, metallurgically bonded alloy layer.
Properties: Provides exceptional, long-term corrosion resistance, protecting the steel even if scratched (sacrificial protection).
Appearance: Characterized by a bright, spangled (crystalline) or matte grey finish.
Application: Ideal for outdoor structures, fencing, handrails, and any application exposed to moisture or weather.
Black Annealed Square Hollow Tube:
Process: The tube is heated to a high temperature and then cooled slowly in a controlled atmosphere. This annealing process alters the steel’s microstructure.
Properties: Becomes significantly softer, more ductile, and less brittle. It relieves internal stresses, making it much more flexible and easier to bend without cracking.
Appearance: Features a characteristic dark grey/black oxide scale on its surface from the heat treatment.
Application: Perfect for bending, forming, and complex fabrication projects like furniture, artistic metalwork, and curved structural elements where flexibility is key.
Materials:Q195, Q235 wire rod or according to request
Tolerance:Wall thickness:+-0.05mm,width:+-0.3mm,length:+-6mm
Application:Widely used in furniture, interior decoration, fluid pipeline, petroleum, and natural gas industry, drilling, pipeline, structure
Packing:In bundle, wrapped with waterproof or as customers’ requirement.
Weight Varies By Profile
Surface Treatments Hot-Dip Galvanizing: Complete corrosion protection for outdoor applications. Powder Coating: Decorative and protective finishes in various colors. Primer Coating: Shop-applied primers for immediate corrosion protection. Self-Color Mill Finish: Natural steel appearance for indoor applications.
Lifetime Limited
20 Years Transferable
Structural Framing: Columns, beams, and trusses for buildings, canopies, and carports.
Architectural & Decorative: Handrails, balustrades, furniture frames, gates, and signage.
General Fabrication: Machine frames, trailer beds, conveyor supports, and safety guarding.
Agricultural & Industrial: Greenhouses, fencing, equipment stands, and storage racks.
Commercial
Industrial
Hot-Dip Galvanizing
Black Finish
Color Spray Paint
Square hollow tubes are a type of steel product manufactured from hot-rolled or cold-rolled steel strip through forming, high-frequency welding, and sizing processes. With such processing, the product offers a square or rectangular cross-section, providing good load-bearing capacity while significantly reducing structural dead weight and improving space utilization. Compared with open-section profiles, square hollow tubes have higher torsional stiffness and better aesthetic appearance, and are widely used in construction, machinery manufacturing, and steel structures.
The standards applied in different countries to set the requirements for square hollow tubes include EN 10219 (cold-formed welded structural hollow sections), EN 10210 (hot-finished structural hollow sections), ASTM A500 (cold-formed welded carbon steel structural tubing), ASTM A513 (electric resistance welded carbon steel mechanical tubing), JIS G3466 (square and rectangular steel tubes for general structure), GB/T 6728 (cold-formed hollow sections for general structure), and others. These standards specify steel grades, size ranges, dimensional tolerances, mechanical properties, process requirements, and delivery conditions for square hollow tubes.
The most frequently followed European standards for producing square hollow tubes are EN 10219 and EN 10210.
EN 10219 applies to cold-formed welded square hollow tubes made from non-alloy and fine grain steels, with a wall thickness generally not exceeding 40 mm. The standard covers the following main steel grades:
Square hollow tubes supplied under EN 10219 are normally delivered in the as-welded, cold-formed, or normalized condition. The standard sets requirements for chemical composition, tensile properties (yield strength, tensile strength, elongation), impact properties (for specific grades and temperatures), and dimensional tolerances (outside dimensions, wall thickness, straightness, squareness, twist). Surface quality shall be consistent with good manufacturing practice. Permissible dimensional and shape tolerances for cold-formed square hollow tubes are specified in EN 10219-2.
EN 10210 applies to hot-finished square hollow tubes made from non-alloy and fine grain steels. Hot finishing is performed by hot forming with subsequent heat treatment, resulting in more uniform mechanical properties, tighter corner radii, and better dimensional accuracy compared with cold-formed tubes. Main steel grades include S235JRH, S275J0H, S355J0H, S355J2H, as well as higher strength grades such as S420NH and S460NH. Hot-finished tubes are generally preferred for applications requiring improved fatigue performance, more precise geometry, or a better surface condition for subsequent coating. Tolerances for EN 10210 products are specified in EN 10210-2.
In North America, square hollow tubes are most commonly produced to ASTM A500 and ASTM A513.
ASTM A500 covers cold-formed welded carbon steel structural tubing for welded or bolted construction of bridges and buildings. Steel grades are classified by yield strength:
The standard specifies requirements for tensile properties, flattening tests, hardness, and dimensional tolerances including outside dimensions, wall thickness, corner radius, and straightness.
ASTM A513 covers electric resistance welded (ERW) carbon steel mechanical tubing for mechanical and general engineering applications. It includes several types:
Square hollow tubes under ASTM A513 are commonly used in machinery, automotive components, conveyors, and furniture.
JIS G3466 is the Japanese standard for square and rectangular steel tubes for general structural purposes. Steel grades include STKR400 and STKR490, with yield strengths of 245 MPa and 325 MPa respectively. The standard covers carbon steel and is widely referenced in Asian construction and manufacturing.
GB/T 6728 is the Chinese standard for cold-formed hollow sections for general structures. Steel grades include Q235B, Q355B, Q420B, and others, corresponding to increasing strength levels. Tolerances and technical delivery conditions are specified in GB/T 6728, and these products are widely used in steel buildings, transmission towers, and machinery frames.
Hot-rolled or cold-rolled steel coils are used as feedstock to produce square hollow tubes. The process begins by slitting the coil into a specific strip width corresponding to the desired tube perimeter. The slit strip is then fed into a series of forming rolls, which gradually shape the flat strip into an open tubular form. The edges are brought together and joined by high-frequency induction welding (HFIW) or high-frequency contact welding (ERW), where the heat generated by the high-frequency current fuses the edges without additional filler metal. The weld seam is then squeezed to remove excess material (flash) and subsequently heat-treated or scarfed to ensure a smooth surface.
After welding, the tube passes through sizing and straightening rolls to achieve final dimensions, squareness, and straightness. For certain applications requiring improved mechanical properties or weld seam reliability, the entire tube or the weld zone undergoes heat treatment, such as normalizing or stress relieving. In the final production stage, square hollow tubes are cut to specified lengths, inspected for dimensional accuracy and surface quality, end-faced (deburred), bundled, labelled, and placed in finished goods storage for shipment.
The industries that primarily consume square hollow tubes include construction, mechanical engineering, automotive manufacturing, furniture production, transmission towers, agricultural equipment, and general fabrication.
In the construction sector, square hollow tubes are widely used for steel columns, beams, trusses, facade structures, handrails, scaffolding, and architectural elements. The key requirements include straightness, consistent corner radii, good weldability, and reliable mechanical properties. High-strength steel grades (e.g., S420MH, S460MH, ASTM A500 Grade C) are increasingly specified to reduce steel tonnage and increase load-bearing capacity.
| Thickness (mm) | Width x Height (mm) | Length (m) |
|---|---|---|
| 2.0 – 8.0 | 40x40 – 200x200 | 6 – 12 |
| 3.0 – 10.0 | 100x50 – 300x200 | 6 – 12 |
Steel grades in high demand: S235JRH, S275J0H, S355J0H, S355J2H, S420MH, S460MH, ASTM A500 Grade B/C, Q235B, Q355B
Delivery conditions: As-welded, normalized, or cold-formed
For machinery frames, conveyor systems, lifting equipment, trailer chassis, and automotive structural components, square hollow tubes must offer consistent mechanical properties, tight dimensional tolerances, and good fatigue performance. The automotive sector often requires tubes with controlled corner radii and smooth internal and external surfaces to facilitate further assembly and coating.
| Thickness (mm) | Width x Height (mm) | Length (m) |
|---|---|---|
| 1.5 – 5.0 | 20x20 – 120x80 | 6 – 12 |
| 2.0 – 6.0 | 50x50 – 150x100 | Custom lengths |
Steel grades in high demand: S235JRH, S355J0H, ASTM A513 Type 2 (DOM), JIS G3466 STKR400, GB/T 6728 Q355B
Delivery conditions: As-welded, stress-relieved, or drawn over mandrel (DOM)
Square hollow tubes for furniture (tables, chairs, shelving) and general fabrication require good surface quality, precise corner squareness, and clean weld seams suitable for painting or powder coating. Thin-wall tubes are preferred to reduce weight while maintaining adequate rigidity.
| Thickness (mm) | Width x Height (mm) | Length (m) |
|---|---|---|
| 0.8 – 2.5 | 15x15 – 80x80 | 4 – 8 |
| 1.0 – 3.0 | 25x25 – 100x50 | 6 |
Steel grades in high demand: S235JRH, ASTM A513, Q235B, DC01 (as base strip)
Delivery conditions: As-welded, pickled or oiled, ready for coating
Large consumers of square hollow tubes include service metal centres, which supply cut-to-length tubes, perforated tubes, or further processed components to end users across various industries. Requirements for geometry, straightness, packaging (bundles, colour coding), and traceability are critical.
| Thickness (mm) | Width x Height (mm) | Length (m) |
|---|---|---|
| 1.0 – 8.0 | 20x20 – 300x200 | 6 – 12 |
Steel grades in high demand: S235JRH, S275J0H, S355J0H, ASTM A500 Grade B, Q235B, Q355B
Delivery conditions: As-welded, deburred, bundled, and tagged
We are committed to fostering enduring partnerships with our clients. Recognizing the unique needs of each customer, we offer customized solutions tailored to their specific requirements. With a focus on flexibility in order processing and punctual delivery, we are dedicated to ensuring customer satisfaction and establishing long-term collaborations built on trust and reliability.
Thank you for your interest in our factory. Should you have any inquiries or require further information regarding our roofing sheets or related services, please feel free to reach out to us. We eagerly anticipate the opportunity to collaborate with you and contribute to your success.
Take the next step – contact one of our experts or explore our full line of metal roof systems.
