Carbon,​Alloy Steel Square & Rectangular Tubes

• ​Introduction

Square & Rectangular Steel Tubes are hollow steel products with square or rectangular cross-sections. They are categorized into seamless and welded types: seamless tubes are formed through hot processing without welds, while welded tubes are made by bending steel strips into shape and welding the seams. These tubes are valued for their high structural efficiency and space-saving design, widely used in industrial and construction fields.

• ​Main Functions

Structural Support：Used in building frames, bridges, and machine bases, their flat surfaces enable stable connections, providing higher lateral stiffness than round tubes.

Mechanical Components：Serve as transmission shafts, brackets, and guide rails in machinery, optimizing assembly space and ensuring precise part alignment.

Application of space Optimization：The non-circular structure of special-shaped pipes gives them significant advantages in space-constrained scenarios, enabling them to adapt to compact spatial layouts.

Decorative Applications：Function as handrails, partition frames, and architectural trims after surface treatment, combining practicality with aesthetics.

• ​Tubing Standards

ASTM A53，ASTM A500； EN 10217-1，EN 10219-1； GB/T 13793，GB/T 3094，GB/T 6728.

• ​Material & Performance

Materials: Square & Rectangular Steel Tubes are crafted from a wide array of materials. Carbon steel is the most commonly used, such as ASTM A500 Grade B/C and Q235, Q355, 10#, 20# steel, which have good plasticity, toughness, and weldability. Alloy steel, such as 40Cr, 20CrMo, is used when higher strength, hardness, and wear resistance are required.​

Performance:​

Mechanical Properties – They have appropriate strength, including tensile strength and yield strength, to bear various loads. The toughness ensures that they are not easy to break under impact.​

Processing Performance – Good plasticity allows them to be processed through cold bending, hot rolling, and other methods to form different cross-sectional shapes. Weldability makes it possible to connect pipes or with other components through welding.

• ​Manufacturing Process

Seamless Square & Rectangular Steel Tubes:

Billet Preparation: Solid steel billets are carefully selected and inspected for purity and quality. The billets are typically made of carbon steel, alloy steel, or stainless steel depending on the required properties of the final product.​

Heating and Piercing: The billets are heated to a high temperature, usually between 1100 – 1250°C. Then, they are pierced using a piercing mill to form a hollow round shell.​

Hot Rolling/Extrusion: The hollow round shell is passed through square of dies with  cross-sections by hot rolling or extrusion processes.

Cold Finishing (Optional): To achieve higher precision in dimensions and better surface quality, a cold drawing or cold rolling process may be applied. This further refines the shape and smoothness of the special – shaped pipe.​

Heat Treatment: Heat treatment processes like annealing or normalizing are carried out to relieve internal stress, improve mechanical properties, and ensure the uniformity of the material’s structure.

Inspection and Testing: Dimensional checks (outer diameter, inner diameter, wall thickness, length) are performed. Non-destructive testing (ultrasonic, magnetic particle) detects internal/surface defects. Mechanical property tests (tensile, hardness) verify compliance with standards. Only qualified products pass all tests.

Welded Square & Rectangular Steel Pipes:​

Strip Uncoiling and Leveling: Coils of steel strips are uncoiled and passed through a leveling machine to ensure a flat and uniform starting material. ​

Forming: The steel strips are bent into the desired Square & Rectangular using roll – forming machines. ​

Welding: The edges of the formed strips are joined together by electric resistance welding (ERW). ​

Sizing and Straightening: After welding, the pipe is passed through sizing machines to ensure that it meets the exact dimensional requirements. Straightening processes are also carried out to correct any deformation that may have occurred during welding or forming.​

Inspection: Weld checks (visual/radiography/ultrasound), dimension tests, some pressure tests.Qualified for delivery.

• Specifications