ERW steel pipe: high-frequency straight-slit electric resistance welded pipe, which adopts hot-rolled wide coil as raw material, and undergoes pre-bending, continuous forming, welding, heat treatment, sizing, straightening, cutting and the like, and has a short weld seam compared with the spiral. The utility model has the advantages of high dimensional precision, uniform wall thickness, good surface quality and high pressure, but the disadvantage is that only small and medium-diameter thin-walled tubes can be produced, and the weld seam is prone to gray spots, unfused, and groove-like corrosion defects. At present, the widely used fields are urban gas, original oil transportation and so on.

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. The advantage is that the same specification can be produced. Steel pipe with diameter specification, the material adapts to a large range, the weld can avoid the main stress, and the force is better. The disadvantage is that the geometrical size is poor.

The length of the weld is longer than that of the straight pipe, which is easy to produce cracks, pores and clips. Welding defects such as slag and welding deviation, and the welding stress is in a tensile stress state. General oil and gas long-distance pipeline design specifications stipulate that spiral submerged arc can only be used in Class 3 and Class 4 areas.

LSAW welded steel pipe: that is, a straight seam submerged arc welded pipe, which is produced by using a single plate as a raw material, pressing (rolling) the steel plate in a mold or a molding machine, and adopting double-sided submerged arc welding and expanding the diameter. The finished product has a wide range of specifications, and the weld has good toughness, plasticity, uniformity and compactness, and has the advantages of large pipe diameter, thick pipe wall, high pressure resistance, low temperature resistance and corrosion resistance.

According to the API standard, in large oil and gas pipelines, when passing through Class 1 and Class 2 areas such as high-altitude zones, seabeds, and urban densely populated areas, straight seam submerged arcs are suitable for the type of Weiyi.