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　　1. Process classification seamless square Square hollow section is divided into hot rolled seamless square pipe hollow section, cold drawn seamless square pipe, extruded seamless square hollow section and welded square  hollow section according to production process.

　　2. The welded square hollow section is divided into: (a) arc welded square pipe, resistance welded square pipe (high frequency and low frequency), gas welded square pipe, furnace welded square pipe (b) straight welded square pipe and spiral welded square pipe according to the welding seam; 3) material classification seamless square pipe according to the material: plain carbon steel square pipe and low alloy square pipe. Ordinary carbon steel is divided into Q195, Q215, Q235, SS400, 20 × steel, 45 × steel, etc.; low alloy steel is divided into Q345, 16Mn, Q390, St52-3, etc.

　　3. Production standard classification ASTM A53 50X50 Galvanized Square Hollow Section is divided into: national standard square hollow section, Japanese standard square pipe, British standard square pipe, American standard square pipe, European standard square pipe and non-standard square pipe.

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