Steel pipes are generally divided into two categories, one is welded steel pipe, and the other is seamless steel pipe.
Welded steel pipe, also called welded pipe, is a steel pipe made of steel plates or strips that are welded after being curled and formed. The production process of welded steel pipes is simple, the production efficiency is high, there are many varieties and specifications, and the equipment investment is small, but the general strength is lower than that of seamless steel pipes. 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. Sewing steel pipe. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of the weld.
The blanks used in welded steel pipes are steel plates or strips. Due to their different welding processes, they are divided into furnace welded pipes, electric welded (resistance welded) pipes and automatic arc welded pipes. Because of their different welding forms, they are divided into two types: straight seam welded pipes and spiral welded pipes. 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. However, compared with straight seam pipes of the same length, the weld length is increased by 30~100%, and the production speed is lower.
Therefore, smaller diameter welded pipes mostly use straight seam welding, while large diameter welded pipes mostly use spiral welding. (For example, the West-East Gas Pipeline uses spiral welded pipes, and Taiyuan Heavy Industry produces spiral pipe welding machines)
There is currently a relatively new technology called “thermal diameter reduction”, which is to roll the welded pipe again to improve its surface quality and dimensional tolerance, so that the overall performance is close to that of seamless steel pipes.