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　　The wall thickness of Welded steel pipe in GB 100 should be 4 mm and 5 mm.

　　Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip after curling and forming, and generally Sizes 6 meters. Welded steel pipe has the advantages of simple production process, high production efficiency, more varieties and specifications, less equipment investment, but its general strength is lower than seamless steel pipe.

　　The common materials of Welded steel pipe are Q235A and Q235C,Q235B, 16Mn, 20#, Q345, L245, L290, X42, X46, X60, X80, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc.

　　The billet used in API 5L 14Inch Carbon Welded Steel Pipe is steel plate or strip. It is divided into furnace welded Steel pipe, electric welded pipe and automatic arc welded Steel pipe because of different welding technology. Because of its different welding forms, it can be divided into straight welded Steel pipe and spiral welded Steel pipe. Because of its end shape, it can be divided into circular welded pipe and special-shaped (square, flat, etc.) welded pipe. Welded Steel Pipe can be divided into the following categories because of their different materials and uses:

　　GB/T3091-2008 (Welded Steel Tube for Low Pressure Fluid Conveyance). Mainly used for conveying water, gas, air, oil, heating hot water or steam and other general low pressure fluids and other purpose pipes. Its representative material is Q235A grade steel.

　　GB/T 14291-2006 (Welded Pipe for Mine Fluid Transport). Mainly used for mine air pressure, drainage, shaft gas drainage with straight seam welded steel pipe. Its representative material is grade Q235A and B steel.

　　GB/T12770-2002 (stainless steel welded steel pipe for mechanical structure). Mainly used for machinery, automobiles, bicycles, furniture, Hotel and hotel decoration and other mechanical parts and structural parts. Its representative materials are 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc.

　　GB/T12771-1991 (stainless steel welded steel pipe for fluid transportation). Mainly used for conveying low-pressure corrosive media. The representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc.

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