Views: 84514 Author: Site Editor Publish Time: 2026-07-31 Origin: Site
Introduction: The Versatility of Square Hollow Sections
Square steel tubes, also known as Square Hollow Sections (SHS), are among the most versatile structural profiles in modern metal fabrication. Characterized by their equal-sided, hollow cross-section, these profiles combine high strength-to-weight ratios with clean aesthetics and ease of connection. Their closed section geometry provides exceptional torsional rigidity—significantly superior to open profiles such as I-beams or channels—making them ideal for applications requiring resistance to twisting forces. The flat, parallel surfaces simplify welding, bolting, and the mounting of brackets, plates, and other components, making square steel tubes a preferred material across construction, mechanical engineering, transportation, and agricultural sectors.
Standard Dimensional Ranges and Global Specifications
Square steel tubes are manufactured in an extensive range of sizes to accommodate diverse structural and mechanical requirements. In metric systems, typical outside dimensions span from as small as 10mm × 10mm up to 400mm × 400mm, with wall thicknesses generally ranging from 0.5mm to 20mm. For light-duty applications such as furniture or ornamental structures, smaller sections (13mm–50mm) with thinner walls (0.5mm–3mm) are typically specified. Medium sections (50mm–150mm) with wall thicknesses of 3mm–8mm serve as the workhorse for general structural framing, machinery bases, and support columns. Large sections exceeding 150mm, often with wall thicknesses up to 12mm or more, are employed in heavy-load-bearing applications. Standard lengths are commonly supplied as 6 meters, 12 meters, or custom lengths.
ASTM A500: The American Standard for Structural Tubing
The most widely used specification for square steel tubes in North America is ASTM A500, which covers cold-formed welded and seamless carbon steel structural tubing for welded, riveted, or bolted construction of bridges and buildings. Under ASTM A500, Grade C is the predominant material, offering a minimum yield strength of 50 ksi (345 MPa) and tensile strength of 62 ksi (427 MPa). The standard encompasses tubes up to a maximum total perimeter of 88 inches, meaning the maximum square HSS size is 22 inches × 22 inches, with wall thicknesses up to 1-inch nominal. For example, a typical square HSS designation under ASTM A500 is expressed as HSS50x50x3, indicating 50mm × 50mm outer dimensions with a 3mm wall thickness. Common imperial sizes range from 1/2″ × 1/2″ with 0.063″ wall thickness up to 8″ × 8″ with 0.250″ (1/4″) wall thickness.
EN 10210 and EN 10219: European Standards for Hot-Formed and Cold-Formed Sections
In Europe, square hollow sections are governed by two primary standards: EN 10210 for hot-finished structural hollow sections and EN 10219 for cold-formed welded structural hollow sections. EN 10219 covers cold-formed welded circular, square, and rectangular structural hollow sections manufactured in wall thicknesses up to 40mm, with square sections available up to 500mm × 500mm outside dimensions. Typical EN 10219 square sections range from 20mm × 20mm with 2.0mm wall thickness up to 300mm × 300mm with wall thicknesses up to 12.5mm or more. The standard specifies dimensional tolerances, sectional properties, and marking requirements, with standard lengths of 6, 8, and 12 meters. Corner radii are also specified: for a 20mm × 20mm × 2.0mm section, the external corner radius is 4mm with an internal corner radius of 2mm.
JIS G3466 and Other International Standards
The Japanese Industrial Standard JIS G3466 specifies requirements for carbon steel square and rectangular tubes used for civil engineering, architecture, and other structures. Dimensional tolerances under JIS G3466 require that for side lengths below 100mm, the tolerance is ±1.5mm; for side lengths exceeding 100mm, the tolerance is ±1.5%. Wall thickness tolerances are ±10%, and weight tolerances are ±10%. Chinese standard GB/T 6728 covers cold-formed steel hollow sections, typically ranging from 20mm × 20mm to 600mm × 600mm, with common material grades including Q235B and Q345B. Common material grades across these standards include ASTM A500 Grades B and C, S235JR, S355J0H, Q235B, and Q345B.
The Square Tube Manufacturing Process: From Coil to Finished Profile
The production of square steel tubes follows a systematic manufacturing workflow that transforms flat steel coil into precision hollow sections. The process begins with raw material preparation, where steel strip—typically hot-rolled or cold-rolled coils of grades such as Q195, Q235, or Q345—is inspected for surface defects and cleaned to remove rust, oil, or other impurities. The coil is then uncoiled and passed through a leveling machine to flatten the strip and relieve internal stress. Edge trimming cuts the steel strip to the required width for square tube production.
The forming stage employs a progressive roll-forming process: the forming mill gradually bends the strip into a round tube, which is then passed through a sizing mill or square reshaping unit that transforms the round tube into a square or rectangular cross-section. High-frequency electric resistance welding (ERW) is then applied to fuse the seam, followed by removal of internal and external weld burrs using scarfing tools. The tube then passes through multiple sizing rollers to fix its final dimensions and form sharp corners as required. Optional online heat treatment, such as annealing, may be applied to the weld seam to improve its quality and overall mechanical performance. A flying saw or fixed-length cutter then cuts the continuous tube to desired lengths. Finally, the cut tubes are straightened to eliminate bends or twists, and end surface grinding or chamfering may be performed. Quality inspection includes visual checks, dimensional verification, and weld inspection using ultrasonic or X-ray testing, followed by anti-rust treatment (such as oiling) and bundling for storage or shipment.
Secondary Processing: Cutting, Bending, and Welding
Beyond primary production, square tubes undergo various secondary processing operations to meet specific application requirements. Cutting can be performed using sawing for general-purpose length cutting, laser cutting for high precision and complex profiles, or plasma cutting for medium-thick tubes. Tube laser cutting uses a high-power fiber laser beam to melt or vaporize tube material locally, offering non-contact, high-energy-density processing with excellent edge quality. Bending transforms straight tubes into curved components for frames, handrails, and architectural elements. CNC tube benders use mandrels and wiper dies to form square tubes into smooth radii without collapsing the walls. Welding assembles individual tube components into larger structures using Gas Metal Arc Welding (MIG) or Gas Tungsten Arc Welding (TIG), with proper joint preparation and fit-up essential for weld quality. Additional secondary processing includes punching, slotting, drilling, and surface finishing such as galvanizing, painting, or powder coating.
