In general, the steel pipe can be classified into two categories: welded steel pipe and seamless steel tube.
Welded steel pipe, also known as welded pipe. It is made of steel sheet or strip steel after crimp forming weld steel pipe. The production technology of welded steel pipe is simple, with the characteristics of high production efficiency, a lot of varieties and specifications, less equipment investment, but the general strength is lower than the seamless steel tube. Since the 1930 s, with the rapid development of high quality rolling production of strip steel and the progress of welding and inspection technology, the weld quality constantly improves, the varieties and specifications of welded steel pipe increases. And it can replace seamless steel pipe in more and more field. According to the form of welding, there are two types: longitudinal welded pipe and spiral welded pipe.
The blank of welded steel pipe is made of steel plate or strip steel. It is divided into furnace welded pipe, welded (erw) tube and automatic arc welding tube because of the different welding process. According to different forms of welding, there are two types: longitudinal welded pipe and spiral welded pipe. On the basis of its end shape, it can be divided into circular welded pipe and alien (square, flat, etc) welded pipe. In terms of different materials and purpose, welded pipe can be classified into the following several varieties:
GB/T3091-1993 (low pressure fluid conveying by galvanized welded steel pipe). It is mainly used for conveying such low pressure fluid as water, gas, air, oil and steam or those hot water for heating. The material is represented by grade Q235A steel.
GB/T14291-1992 (welded steel pipe for conveying mine fluid). It is mainly used in longitudinal welded pipe for compressed air, drainage and discharge gas. The material is represented by Q235A.
GB/T14980-1994 (large diameter welded steel pipe for conveying low pressure fluid). It is mainly used for conveying low pressure fluid such as air, steam, water, sewage, gas, etc. Its representative material is Q235A steel.
GB/T12770-1991 (stainless steel welded steel tube for mechanical structure). It is mainly used in machinery, automobile, bicycle, furniture, hotel and restaurant decoration and other mechanical parts and components. Its representative material are OCr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc.
GB/T12771-1991 (stainless steel welded steel tube for conveying fluid). It is mainly used for low pressure and corrosive medium. The material is represented by 0Cr13、0Cr19Ni9、00Cr19Ni11、00Cr17、0Cr18Ni11Nb、0017Cr17Ni14Mo2, etc.
The characteristics of longitudinal welded pipe are simple production technology, high production efficiency, low cost and rapid development. The strength of the spiral welded pipe is generally higher than longitudinal welded pipe. People can use a narrow blank to produce a larger diameter welded pipe. Also, using the same width of blank can produce different-diameter welded pipes. But compared with the longitudinal welded pipe of the same length, the welding length increases by 30 ~ 100%, and the production speed is lower.
Therefore, small diameter welded pipes are mostly welded by straight welding, while the larger diameter welded pipes are mostly welded by spiral welding. (for example, the spiral welded pipe is used in the west-east gas pipeline.)
At present, There is a relatively new technology, called "hot reducing". That is hot rolling the welded pipe again, in order to improve the surface quality and dimensional tolerance and make its comprehensive performance be close to the seamless steel tube.
