Welded steel pipe is a seamed steel pipe. The production process is to bend the pipe blank (steel plate and steel strip) into a tube of the required cross-sectional shape and size by various forming methods, and then weld the weld by different welding methods. The process of obtaining a steel pipe. Compared with seamless steel pipes, welded pipes have the characteristics of high product precision,especially wall thickness accuracy, simple main equipment, small footprint, continuous operation in production, flexible production, and wide product range of the unit.
From the production process,welded pipes are further divided into: Spiral Submerged Arc Welding; LSAW (Longitudinally Submerged Arc Welding); ERW (Electric Resistance Welding).
ERW steel pipe: high-frequency straight-slit electric resistance welded pipe, which adopts hot-rolled wide-rolled material as material, through pre-bending, continuous forming, welding, heat treatment, sizing, straightening, cutting and other processes, compared with spiral, it has short weld seam, standard The precision is high, the wall thickness is uniform, the surface quality is good, and the pressure is high-grade, but the defect is that only small and medium-diameter thin-walled tubes can be produced, and the welds are prone to gray spots, unfused, and groove-like corrosion defects. The more widely used areas nowadays are urban gas and crude oil products.
SSAW steel pipe: spiral submerged arc welded pipe. When the coiled pipe is rolled, its advancing direction has a forming angle (adjustable) with the center line of the forming pipe. When the forming pipe is welded, the weld is spiraled, and the profit is the same standard. For steel pipes of standard diameter, the material xi has a large conventional plan, the weld can avoid the main stress, the force is better, the defects are a few standards, the length of the weld is longer than that of the straight pipe, and the crack slag is easy to crack. Welding defects such as welding deviation, the welding stress is tensile stress. General oil and gas long-distance pipeline design standard rules spiral submerged arc can only be used in Class 3 and Class 4 areas.
LSAW steel pipe: that is, straight seam submerged arc welded pipe, which is made by pressing a single sheet of medium and thick plate as a material in a mold or a molding machine, and adopting double-sided submerged arc welding method and expanding the diameter to produce. The standard planning of its products is wide, the weldability, plasticity, uniformity and fineness of the weld are good, and it has the advantages of large pipe diameter, thick pipe wall, high pressure resistance, low temperature resistance and corrosion resistance. When creating high-strength, high-resistance, high-quality long-distance oil and gas pipelines, most of the required steel pipes are large-diameter thick-walled straight seam submerged arcs. According to the API standard rules, in the large-scale oil and gas transportation pipelines, when passing through the sub-area of the alpine zone and the densely populated areas of the city, the straight seam submerged arc is only the designated applicable pipe type.