Quality requirements and industry standards for square tube

Date:2024-04-30Tags:Square tubes, rectangular tubes, tube

What is a square tube?

Square tube and rectangular tube are two commonly used steel pipe materials in construction projects. Square tube is a hollow square cross-section lightweight thin-walled steel pipe, also known as steel cold-bent profile. It is a square section steel with a square cross-section shape and size made of Q235 hot-rolled or cold-rolled strip or coil as the base material, cold bending and then high-frequency welding. In addition to the thickening of the wall thickness, the corner size and edge straightness of hot-rolled extra thick-walled square tubes reach or even exceed the level of resistance welded cold-formed square tubes. It has good comprehensive mechanical properties, good weldability, cold and hot processing properties and corrosion resistance, and has good low-temperature toughness. Square tube is a hollow square cross-section lightweight thin-walled steel tube, which can also be called steel cold-bent profile. Because of its good mechanical properties, it has its application fields in the construction industry, machinery manufacturing industry, and steel construction projects.

square tube

Quality requirements for square tube

1. Material requirements

The material of square tubes should meet the requirements of relevant standards and specifications. Generally speaking, the commonly used materials for square tubes include carbon steel, stainless steel, alloy steel, etc. Different application scenarios and working environments require the selection of different materials to ensure that the pipes have sufficient strength, corrosion resistance and wear resistance.

2. Dimensional accuracy requirements

The dimensional accuracy of square tubes is one of the important indicators of their quality. The accuracy of dimensional parameters including outer diameter, wall thickness, length, etc. should comply with relevant standards and technical requirements. Especially for applications in precision engineering and equipment, the dimensional accuracy requirements for square tubes are more stringent.

3. Surface quality requirements

The surface quality of the square tube directly affects its appearance and service life. The surface should have no obvious pores, cracks, scars, unevenness and other defects, and should be treated with anti-rust treatment to ensure that it is not prone to rust and corrosion during use.

4. Strength and pressure resistance performance requirements

The strength and pressure resistance of square tubes are important performance indicators when they bear external loads. Pipes should have sufficient strength and stiffness to withstand the pressure and mechanical loads under designed working conditions to ensure the safe operation of the pipeline system.


The quality requirements of square pipes are the key to ensuring good performance and reliable quality of square pipes during use. By strictly controlling the quality requirements in terms of materials, dimensions, appearance, chemical composition and mechanical properties, we can ensure that the quality of square tubes meets relevant standards and specifications and meets the needs of users. The quality requirements of square tubes are an indispensable part of the production and application of square tubes and the basis for the continuous development of the square tube industry. Our company produces high-quality square tubes through strict quality requirements to provide users with better products and services.


What are the standards for square  tubes in different industries?

1. The allowable deviations of the outer diameter and wall thickness of steel pipes should comply with regulations. Table: Allowable deviation of outer diameter + 0.50mm-0.20mm. Allowable deviation of wall thickness + 0.97mm-0.77mm. The usual length of steel pipe is 9400mm~9750mm.

2. The bending degree of the steel pipe shall not be greater than 1.0mm/m. The end faces of both ends of the steel pipe should be perpendicular to the axis of the steel pipe, and the cut burrs should be removed.

3. Compactness Steel pipes should be subjected to eddy current testing one by one to check the compactness of the steel pipes. The diameter of the artificial defect hole in the eddy current testing comparison sample is φ2.2mm±0.01mm.

4. Each bundle of steel pipes weighs no more than 2 tons, and the surface of the steel pipes should be coated with anti-corrosion oil. After negotiation between the supply and demand parties and indicating it in the contract, the mark can also be stipulated in the agreement.

5. Mechanical properties After proper heat treatment, the mechanical properties of the steel pipe should meet the requirements of N80 steel grade in API SPEC 5CT.


Common standards for square tubes

The standard of square tube refers to the unified specification of materials, sizes, shapes and technical requirements used to produce square tubes. Depending on different application scenarios, the standards of square tubes may vary. The following are some common square tube standards and their related contents:

1. GB/T 3091-2008 (Steel galvanized square tube)

This is one of the Chinese standards that specifies the production requirements of galvanized square tubes. Galvanized square tubes are mainly suitable for structural purposes and are widely used in construction, machinery and other industries.
Size: The square tube specifications of GB/T 3091-2008 standard generally include a range of 20×20mm to 400×400mm, and the wall thickness ranges from 1.5mm to 12mm.
Material: This standard requires the use of low-carbon steel materials such as Q235, which have good plasticity and weldability.

2. GB/T 6728-2002 (Cold-bent thin-walled steel for building structures)

The GB/T 6728 standard specifies the technical requirements for cold-bent square tubes for building structures, which are often used in building structures, mechanical equipment and other fields.
Size range: The size of this standard square tube is usually 20×20mm to 200×200mm, and the wall thickness is generally 1.5mm to 6mm.
Material requirements: Q235 steel, Q345 steel, etc. are used, which meet certain tensile strength and yield strength requirements.

3. ASTM A500 (USA)

The ASTM A500 standard applies to square tubes produced in the United States, mainly used for cold-formed and welded steel tubes in the fields of construction, structure, machinery, etc.
Size range: The size of this standard square tube ranges from 1/2 inch to 16 inches, and the wall thickness is usually 0.083 inches to 0.5 inches.
Material requirements: Structural steel, such as A36 or high-strength low-alloy steel, is used, and good tensile strength and toughness are required.

4. EN 10219 (Europe)

The EN 10219 standard applies to the European market, especially for square tube products used in steel structures and building structures.
Size range: The size of square tubes of this standard generally ranges from 20×20mm to 500×500mm, and the wall thickness can be adjusted according to demand, commonly 2mm to 12mm.
Material requirements: Meet S235, S275 and other steel grades, and require good weldability and corrosion resistance.

5. JIS G 3466 (Japan)

The JIS G 3466 standard is applicable to the Japanese market, mainly square tubes used in engineering fields such as construction and bridges.
Size range: The size of square tubes of this standard ranges from 25×25mm to 200×200mm, and the wall thickness is usually between 1.5mm and 6mm.
Material requirements: Structural steels such as SS400 are usually used, with good plasticity and weldability.

6. API 5L (Oil and Gas Industry)

The API 5L standard is applicable to square tubes in the oil and gas industry, and is usually used in oil and gas transmission pipelines and pipeline structures.
Size range: The size of square tubes can be customized according to project requirements, and usually have a larger wall thickness.
Material requirements: Steel grades of X42, X52, and X60, with high compression and corrosion resistance.

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