Steel pipes are generally divided into two categories, one is called welded steel pipes, and the other is seamless steel pipes.
Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip steel after crimping and welding. Welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment investment, but its general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of continuous rolling production of high-quality strip steel and the advancement of welding and inspection technology, the quality of welds has continued to improve, and the varieties and specifications of welded steel pipes have increased day by day, replacing unfinished steel pipes in more and more fields. Seam steel pipe. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of the weld seam.
The blanks used for welded steel pipes are steel plates or strip steel, which are divided into furnace welded pipes, electric welding (resistance welding) pipes and automatic arc welded pipes due to their different welding processes. Because of its different welding forms, it is divided into two types: straight seam welded pipe and spiral welded pipe. Because of their end shapes, they are divided into round welded pipes and special-shaped (square, flat, etc.) welded pipes. Welded pipes are divided into the following varieties due to their different materials and uses:
GB/T3091-1993 (Galvanized welded steel pipe for low-pressure fluid transportation). It is mainly used to transport water, gas, air, oil, heating hot water or steam and other general lower pressure fluids and other pipes. Its representative material is Q235A grade steel.
GB/T3092-1993 (Galvanized welded steel pipe for low-pressure fluid transportation). Mainly used to transport water, gas, air, oil, heating hot water or steam and other general lower pressure fluids and other pipes. Its representative material is: Q235A grade steel.
GB/T14291-1992 (Welded steel pipe for mining fluid transportation). It is mainly used for straight seam welded steel pipes for mine air pressure, drainage and shaft gas discharge. Its representative materials are Q235A and B grade steel. GB/T14980-1994 (Large-diameter electric welded steel pipe for low-pressure fluid transportation). Mainly used for transporting low-pressure fluids such as water, sewage, gas, air, heating steam and other purposes. Its representative material is Q235A grade steel.
GB/T12770-1991 (Stainless steel welded steel pipes for mechanical structures). Mainly used in machinery, automobiles, bicycles, furniture, hotel and restaurant decoration and other mechanical parts and structural parts. Its representative materials include 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc.
GB/T12771-1991 (Stainless steel welded steel pipes for fluid transportation). Mainly used to transport low-pressure corrosive media. Representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc.
The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is rapid. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Welded pipes with larger diameters can be produced from narrower billets, and welded pipes with different diameters can also be produced from billets of the same width. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower.
Therefore, most of the welded pipes with smaller diameters adopt straight seam welding, and most of the large diameter welded pipes adopt spiral welding. (For example, the pipelines of the West-East Gas Pipeline use spiral welded pipes, and Taiyuan Heavy Industry produces spiral welded pipe machines) At present, there is a relatively new technology called “thermal reduction”, which is to reroll the welded pipes to improve its surface quality and The dimensional tolerance makes the overall performance close to that of seamless steel pipes.