The square steel pipe is a term for square pipes which have the equal side length and rectangular pipes which have the unequal side length. The square steel pipe is made by the strip steel with the rolling process. Generally, the strip steel will be unpacked, flattened, curled and welded to be a round pipe, be rolled into a square pipe, and will be cut into the needed length. Square steel pipes are mainly used in fields including the mechanical industry, the chemical industry, shipbuilding, oil casings and pipelines for transporting water, gas, sewage, etc.

Standards and applications of square steel pipes

1. The standard number of the galvanized welded square steel pipes for transporting low pressure fluid is GB/T3091-2008. The typical materials of galvanized welded square steel pipes are Q235A, Q235B, Q345B, etc. Galvanized welded square steel pipes are mainly used for transporting water, coal gas, air, oil, hot water or steam, and they are limited to the transportation of low-pressure fluid.

2. The standard number of the mining welded square steel pipe is GB/T14291-2000.

3. The standard number of the large-diameter welded square steel pipes for transporting low pressure fluid is GB/T14980-1994, and the typical materials of these pipes are Q235 Grade A and Grade B. The large-diameter welded square steel pipes are mainly used to transport the low pressure fluid such as water, sewage, coal gas and air.

4. The standard number of the stainless welded square pipes for transporting fluid is GB/T12771-1991, and the typical materials of these pipes are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo, etc. The stainless welded square pipes are mainly used for transporting low pressure corrosive media.

5. The standard number of the spiral welded square pipe for transporting low pressure fluid is SY/T5037-2008, and the typical materials of these pipes are Q235B, Q345B, etc. The spiral welded square steel pipe are mainly applied to low pressure pipelines for transporting water, oil, natural gas, etc.

6. The standard number of the square pipe for transporting flammable fluid and non-flammable fluid is B/T9711.1（GB/T9711.2）-1997, and the typical materials of these pipes are from L245 to L415. The requirements on these pipes are usually high.