How to identify the quality of 1/8 square steel pipe

• 1/8 square tube is a name for square tube and rectangular tube, that is, a hollow tube with equal side lengths and unequal side lengths. It is made of strip steel that has been processed and rolled. Generally, the strip is unpacked, flattened, coiled, welded to form a round tube, and then rolled into a square tube from the round tube and then cut to the required length. Commonly used welding processes are arc welded square tubes and resistance welded square tubes (high frequency, low frequency).

• 1/8 square steel pipe is used in engineering construction, glass curtain wall, door and window decoration, steel structure, guardrail, machinery manufacturing, automobile manufacturing, home appliance manufacturing, shipbuilding, container manufacturing, electric power, agricultural construction, agricultural greenhouse, bicycle rack, motorcycle Shelves, racks, fitness equipment, leisure and travel supplies, steel furniture, oil casings of various specifications, oil pipes and line pipes, water, gas, sewage, air, heating and other fluid transportation, fire protection and supports, construction, etc.

• The authenticity identification method of 1/8 square tube can be judged by observing the surface smoothness and flatness of the square tube. If the surface of the square tube is relatively flat, it can reflect that the square tube is good. Not so flat, and the size and thickness are not standardized, it can reflect that the square tube is a poor quality product.

4x4square steel pipe standard for different uses

1. Galvanized welded square tube for low-pressure fluid transportation, the standard number is GB/T3091-2008. Representing material Q235A, Q235B, Q345B, etc. Mainly used to transport water, gas, air, oil and heating hot water or steam, the use is limited to general lower pressure fluids.

2. Galvanized welded square tube for low-pressure fluid transportation, the standard number is GB/T3092-2008. The representative material is the same as above. It is mainly used to transport general low pressure fluids such as water, gas, air, oil and heating hot water or steam.

3. Welded square pipe for mining fluid transportation, the standard number is GB/T14291-2000. The representative material is Q235A and B grade steel, which is mainly used for straight seam welded square pipes for mine air pressure, drainage and shaft discharge gas.

4. Large-diameter electric welded square tube for low-pressure fluid transportation, the standard number is GB/T14980-1994. Represents the material Q235AB grade. It is mainly used to transport low-pressure fluids such as water, sewage, gas, air, and heating steam.

5. Stainless steel welded square tube for fluid transportation, the standard number is GB/T12771-1991. The representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc. Mainly used for conveying low pressure corrosive medium.

6. The standard number of the spiral square pipe for low-pressure transportation (standard of the Ministry of Petroleum) is SY/T5037-2008. The representative material is carbon steel such as Q235BQ345B. Mainly used for low-pressure transportation of water, oil, natural gas, heating and other pipelines.

7. Square pipes for conveying flammable and non-flammable fluids, the standard number is GB/T9711.1 (GB/T9711.2)-1997. The representative material is L245-L415, such as steel for pipelines. It is mainly used to transport flammable and non-flammable fluids with low pressure or high pressure, and the requirements are relatively high.

Q235 Q235A Q235B Q345B 4x4square steel pipe performance

• Q235 4x4square steel pipe is ordinary carbon structural steel - ordinary plate, low alloy steel (C<0.2%). A large number of buildings and engineering structures are used to make steel bars or to build factory buildings, high-voltage transmission towers, bridges, vehicles, boilers, containers, ships, etc., and also a large number of mechanical parts that do not require high performance. C, D grade steel can also be used as some professional steel. (Q represents the yield of this material, and the 345 in the back refers to the yield value of this material, which is around 345. The yield value will decrease as the thickness of the material increases)  

• Q235B 4x4square steel pipe has certain elongation, strength, good toughness and castability, easy to punch and weld, widely used in the manufacture of general mechanical parts. It is mainly used for welded structural parts with high quality requirements in construction and bridge engineering.

• The difference between Q235A 4x4square steel pipe and Q235B4x4square steel pipe: all steels belong to carbon steel. In the national standard GB700-2006, the material distinction between Q235A and Q235B is mainly in terms of the carbon content of the steel. The carbon content of the steel made of Q235A is not more than 0.22%, and the carbon content of the steel made of Q235B is not more than 0.20%; The material of Q235A is not subjected to impact test, but the material of Q235B is subjected to impact test at room temperature, with V-notch. Relatively speaking, the mechanical properties of steel made of Q235B are far better than those of steel made of Q235A. Under normal circumstances, steel mills mark the finished profiles on the identification plates before they leave the factory.

• The surface strength and wear resistance of Q345B 4x4 rectangular tube can be used for surface treatment of Q345B 4x4 rectangular tube, such as flame surface, high frequency induction quenching, organic chemical heat treatment process, etc. Generally speaking, heat treatment is common for high and high frequency surface layers, and the heating temperature is 850-950 degrees. Because of the poor heat transfer, the heating rate should not be too fast, otherwise melting cracks and heat treatment cracks will occur, which can ensure the strength and wear resistance of the surface layer of the rectangular square tube.

The reliability of the high-precision Q345B square and rectangular pipe specification stipulates that the precision of the pipe fittings is maintained for a long time. Due to the low cooling speed, straightening in the air has a stable and practical effect, increasing the total number of Q345B square and rectangular tubes remaining in the structure, and it is necessary to carry out cold violence.

The high toughness Q345B square tube is mainly affected by the contact fatigue load effect, so it must have high toughness. Therefore, heat treatment, induction hardening or organic chemical heat treatment should be carried out, followed by ultra-low temperature quenching.

The difference between Q235 4x4square steel pipe and Q345 4x4square steel pipe  

• The yield strength is different: the lower limit of the yield strength of Q235 is 235MPa, and the lower limit of the yield strength of Q345 is 345MPa (Q means "yield" in Chinese characters, and the following value represents the lower limit of yield strength)

• Alloy content is different: Q235 is ordinary carbon steel, Q345 is low-alloy steel, Q235 is carbon structural steel, compared with the old standard GB700-79 grades A3, C3 Q345 is low-alloy structural steel, compared with the old standard 1591-88 grades 12MnV , 16Mn 16MnRE, 18Nb, 14MnNb As for performance and application, there are too many, Q235--metal structural parts, carburized or cyanided parts that do not require high core strength, tie rods, connecting rods, hooks, couplers, bolts and nuts, Sleeves, shafts and welding parts Q345--good comprehensive mechanical properties, low temperature performance, good plasticity and weldability, used for medium and low pressure vessels, oil tanks, vehicles, cranes, mining machinery, power stations, bridges, etc. Structures, mechanical parts, building structures, general metal structural parts, used in hot-rolled or normalized state, and can be used in various structures in cold regions above -40°C. If the structure is controlled by strength, Q345 can be considered. If the structure is controlled by stiffness, Q235 can be considered. The price of Q345 is slightly more expensive, but because of its high strength, it can save materials.