Up to now, carbon steel and low alloy steel are still the most commonly used oil and gas field surface gathering and transportation pipes. After decades of application and experience accumulation, the manufacture, construction and acceptance of carbon steel and low alloy steel are also the most mature compared to other types of pipes.
According to different types of pipes, carbon steel and low alloy steel pipes can be divided into high frequency resistance welded pipes (HFW), spiral submerged arc welded pipes (SAWH), straight seam submerged arc welded pipes (SAWL) and seamless steel pipes (SMLS).
Restricted by the manufacturing process and equipment manufacturing capacity, the scope of application of different pipe types pipe is different. Among them, the submerged arc welded pipe is mainly large-diameter steel pipe, and the highest steel grade L555M submerged arc welded pipe currently used in China can reach a diameter of 1422 mm; high-frequency resistance welded pipe is usually mainly medium-diameter steel pipe, and due to the lack of deposited metal at the weld seam during its manufacture, the defect rate of the weld seam and the heat-affected zone is higher than that of other types of pipes, and therefore is usually applied only to the working conditions of 6.3 MPa or less; seamless steel pipe is made of steel ingots, hot rolled, extruded or cold-drawn. Seamless steel pipes are made from steel ingots that are hot rolled, extruded or cold drawn, and are suitable for small and medium diameter pipes with thicker wall thicknesses than welded pipes.
According to the use of different temperatures, carbon steel and low alloy steel can be divided into two categories of ordinary steel and low temperature steel. The limit of distinction is generally -20 ℃, applied in -20 ℃ below the environment of the steel for cryogenic steel, applied in -20 ℃ above the environment of the steel for ordinary steel. Compared with ordinary steel, cryogenic steel has superior resistance to brittle fracture, crack initiation and crack stopping. Its low temperature resistance is usually measured by the Charpy impact absorption energy of the pipe at low temperatures, and can also be tested by the low temperature drop test for pipes with an outside diameter of 508 mm or more.The application of L555M cryogenic pipeline steel in the China-Russia East Route demonstrates that it can be used in extreme cold conditions at -40 °C.
