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　　Firstly, hollow sections for low pressure fluid transportation, code No. GB/T3091-2008. Represents raw materials Q235A, Q235BQ345B, etc. Hollow sections is primarily used for transporting water, gas, air, oil and heating hot water or steam. Hollow sections is limited to generally low pressure fluids.

　　Second, hollow sections for low-pressure fluid transportation, code No. GB/T3092-2008. Ibid., for raw materials.Hollow section is mainly used for transporting water, gas, air, oil, heating hot water or steam and other usually low pressure fluids. Hot Dipped Galvanized Steel Rectangular Hollow Section is selected for the surface of large-caliber square pipe.

　　Thirdly, the hollow section is transported by mining fluid. The code number is GB/T 14291-2000. Represents raw materials Q235A and B grade steel. Hollow section is mainly used for vertical seam welding square pipes for mine air pressure, drainage and shaft gas discharge.

　　Fourth, hollow section for low pressure fluid transportation, code No. GB/T14980-1994. Represents raw material Q235AB. Hollow section is mainly used for transporting low-pressure fluids such as water, sewage, gas, air and heating steam.

　　Fifth, hollow section for mechanical layout, code No. GB/T12770-1991. Represents raw materials 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc. Mainly used for machinery, automobiles, bicycles, furniture, Hotel and restaurant decoration and other mechanical parts and layout parts.

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