Welded steel pipe, also known as welded pipe, is a steel pipe which welded by steel plate or strip after the coil shaping. Welding steel pipe is simple in production process, high in production efficiency, various in specifications, and the equipment capital is not much. Generally, the strength of welded steel pipe is lower than the seamless steel pipe. Since the 1930s, with the rapid development of rolling production of high quality cold rolling strip steel and progress of welding and inspection technology, welding quality continuously improve. What’s more, specifications of welding steel pipe are increasing and instead of the seamless steel pipe in more and more fields. According to the form of Welded steel pipe weld, it is divided into longitudinal and spiral welded pipe. 

Welded steel pipe used steel plate or strip as blank, because of its welding process; it is divided into furnace pipe, welding (resistance welding) pipe and automatic arc welded pipe. Because of the different forms of welding, it is separated as longitudinal welded pipe and spiral welded pipe. For its end shape, it is divided into circular welded pipe and shaped (square, flat, etc.) welded pipe. Welded pipe is divided into the following several varieties because of its material and use:

GB/T3091-2001 (galvanized welded steel pipe for low pressure fluid delivery). Mainly used for conveying low pressure fluid, such as water, gas, air, oil and heating hot water or steam and other purposes. Its representative material is: Grade Q235 steel.

GB/T14291-2006 (welded steel pipe for mineral fluid transport). Mainly used in air pressure, drainage of mine.  Its representative material is: Grade B steel, Q235A steel. 

GB/T14980-1994 (large diameter welded steel pipe for low pressure fluid delivery). Mainly used for conveying low pressure fluid such as water, sewage, gas, air, heating steam and other applications. Its representative material is: Grade Q235A steel.

GB/T12770-2002 (stainless steel welded pipe for mechanical structure). Mainly used in machinery, automobiles, bicycles, furniture, hotels and hotel decoration and other mechanical components and structural parts. Its typical material is: 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc..

GB/T12771-1991 (fluid transport with stainless steel welded pipe). Mainly used for conveying low pressure corrosive medium. Its typical material is: 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc..

In addition, decorative stainless steel welded pipe (GB / T 18705-2002), building decorative stainless steel welded pipe JG/T 3030-1995, low pressure fluid conveyor with large diameter welded steel pipe (GB / T 3091-2001) and heat exchange welding steel pipe (YB4103-2000).

The welded pipe can be produced different pipe with the same width of the billet. But compared with the same length of straight pipe, the weld added more 30~100% of the length, and the production rate is low.

Therefore, most of the welded pipe with small radius used straight welding, while the large diameter welded pipe mostly used spiral welding.