According to the manufacturing process of steel pipe, seamless steel pipe can be divided into (SML), as the main oil gathering pipe and the small caliber high pressure natural gas pipeline, the number for the long oil pipeline is very few, most of the pipeline is the use of high-frequency welded pipes (ERW
), spiral submerged arc welding pipe (SSAW)
and LSAW (LSAW) three. The following table for several technological characteristics of the steel pipe and the quality of performance comparison: high-frequency welded pipes (ERW) according to the different welding modes are divided into induction welding and contact welding in two forms, the hot-rolled steel coil as raw material, after pre bending, continuous molding, welding, heat treatment, sizing, straightening, cutting and other processes. Compared with the spiral welded seam with short, high dimensional accuracy, uniform thickness, good surface quality, high pressure, but the drawback is the production of small diameter thin-walled tube only, weld is easy to produce gray spot and lack of fusion, groove corrosion defects.
At present, the widely used fields are city gas, crude oil delivery and so on. Spiral submerged arc welded pipe (SSAW) is the direction of strip rolling and forming tube center line forming angle (adjustable), side molding and welding, the welding seam of the spiral line, has the advantages of steel strip with the same specification can produce a variety of diameter specifications, raw materials to a large range, can avoid the weld stress well, the force, disadvantage is the geometric size of poor weld length compared to straight pipe length, cracks, porosity, slag, weld offset of welding defects, the welding stress is tensile stress. The general oil and gas pipeline design specification stipulates that the spiral submerged arc welding pipe can only be used in 3 types and 4 types. This process improved the foreign raw materials will be changed into the steel, forming and welding separated by pre welding and lean, after welding cold expansion, the welding quality is close to UOE, currently there is no such process, is our country the improvement direction of the spiral tube factory. The spiral tube used in the "west to East Gas Transmission" is still produced according to the traditional process, but the pipe end has been expanded. The United States, Japan and Germany's overall negative SSAW, that the main line is the use of SSAW; Canada and Italy part of the use of SSAW, Russia's use of a small amount of SSAW, and has formulated the supplementary conditions very strict, due to historical reasons, most of the domestic trunk or the use of SSAW.
Submerged arc welding (LSAW) is a single thick plate as raw materials, the steel plate in the mold or molding machine pressure (volume) into the tube, using double-sided submerged arc welding and expanding into production. Its finished product specification range is wide. The toughness, plasticity, uniformity and compactness of the weld are good. It has the advantages of large diameter, thick wall, high pressure resistance, low temperature resistance and strong corrosion resistance. In the construction of high strength, high toughness and high quality long distance oil and gas pipeline, most of the steel pipes required are large diameter thick wall straight seam submerged arc welded pipe. According to the API standard, in large oil and gas transmission pipeline, when passing through 1 or 2 kinds of areas, such as alpine region, seabed and urban densely populated area, the longitudinal submerged arc welded pipe is the only applicable pipe type. According to the different molding methods can be divided into: UOE pipe: single steel plate at the edge of the pre bending, U molding, O molding, welding, welding, machinery in the cold expansion process; JCOE pipe: according to the "J-C-O-E" pre welding, molding, welding after the cold expansion process of HME pipe; the mandrel rolling method according to the "C-C-O" forming and welding after the cold expansion process