The difference between ERW, SSAW and LSAW

According to different manufacturing processes, steel pipes can be divided into (SML). As the main oil gathering pipe and small caliber high-pressure natural gas pipeline, the number of long oil pipelines is very small. Most of the pipelines are divided into three types: high frequency straight seam (ERW), spiral submerged arc (SSAW) and submerged arc (LSAW). The following table is the comparison of several technical characteristics and quality performance of steel pipe: longitudinal high frequency (ERW) can be divided into induction welding and contact welding according to different welding methods. Hot rolled wide roll is used as raw material, after pre bending, continuous forming, welding, heat treatment, sizing, straightening, cutting and other processes, compared with spiral welding, the weld is short, high precision, uniform thickness, good surface quality and resistance High pressure, but the disadvantage is only to produce small diameter thin-walled pipe, the weld is easy to produce gray spots and lack of fusion, groove corrosion defects. At present, the widely used fields are city gas, crude oil transportation, etc. SSAW is the forming angle of the rolling direction and the forming pipe centerline (adjustable). When side molding and welding, the weld of the spiral line has the advantages of producing various specifications of steel pipes of the same specification. Diameter specification, wide range of raw materials, avoidable stress of weld, good stress, disadvantages are poor geometric size, weld length, weld length, crack, pore, slag, weld offset, welding defect, poor welding stress is tensile stress. According to the general oil and gas pipeline design code, spiral submerged arc can only be used in three types and four types of areas. The improved foreign raw materials of this process will be transformed into steel. Through pre welding and lean separation molding and welding, cold expansion after welding, the welding quality is close to UOE. At present, there is no such process. Our factory is in the direction of improvement. "West to East Gas Transmission" is still used in the traditional way, but the end of the pipeline has been expanded. The United States, Japan and Germany generally deny SSAW, and think that SSAW is mainly used; Canada and Italy use part of SSAW, Russia use a small amount of SSAW, and have formulated very strict supplementary conditions. Due to historical reasons, most domestic trunk lines still use SSAW. Longitudinal submerged arc welding (LSAW) is to use single thick plate as raw material, pressurize steel plate in mould or forming machine (volume), adopt double-sided submerged arc welding and expand production. Its finished products have a wide range of specifications. The toughness, plasticity, uniformity and compactness of the weld are all very good. The utility model has the advantages of large diameter, thick wall, high pressure resistance, low temperature resistance and strong corrosion resistance. In the construction of long-distance oil and gas pipelines with high strength, toughness and quality, most of the steel pipes are LSAW with large diameter and thick wall. According to API standards, in large oil and gas pipelines, when passing through 1 or 2 areas (such as high mountains, seabed and densely populated urban areas), longitudinal submerged arc is the only designated pipeline type. According to different forming methods, it can be divided into: UOE: pre bending of single steel plate at the edge, U-forming, O-forming, welding, welding, and mechanical cold expansion process; JCOE: pre welding, forming, and cold expansion process after welding according to "j-c-o-e"; HME: rolling forming and welding after cold expansion process according to "C-C-O" method through mandrel