Transport pipes (such as stainless steel pipes) have seamless steel pipes and welded steel pipes according to different pipe processing processes. seamless steel pipes are widely used in oil field internal gathering pipes and small-caliber high-pressure natural gas pipelines, and is rarely used for long-distance transportation of oil and gas. Most of the long-distance transportation pipes are made of three types: electric resistance welding pipe(ERW), spiral submerged arc welded pipe (SSAW) and submerged-arc longitudinal welded pipe (LSAW).

Electric resistance welding pipe (ERW) is divided into induction welding and contact welding according to different welding modes. Hot rolled stainless steel wide-band coil or other coil is used as raw material and processed by pre-bending, continuous forming, welding, heat treatment, sizing, straightening and cutting. Compared with spiral welded pipe, ERW has the advantages of short weld, high dimensional accuracy, uniform wall thickness. The surface quality of stainless steel pipe is good and the pressure is strong, but the disadvantage is that only small and medium-sized thin-walled pipes can be produced. The welds of stainless steel pipes are easy to form gray spots, unfused, grooved corrosion defects and so on. At present, this kind of welded pipe is widely used in the transportation of city gas and crude oil products.

Spiral Submerged Arc Welded Pipe (SSAW) is a kind of spiral welded pipe, which guarantees the adjustable forming angle between its forward direction and the center line of the formed pipe, and then welds while forming. Therefore, the weld of the product is spiral. The advantage of this kind of welded pipe is that the same specification of strip steel can be used to process steel pipes of various diameter specifications. Its raw material has a wide range of adaptability and the weld can avoid the main stress. The stress condition is good, but its disadvantage is that the geometric size is poor, the length of the weld is longer than that of the straight weld pipe, and it is easy to form welding defects such as cracks, blowhole, slag inclusion and welding deviation.

Longitudinal submerged arc welded pipe (LSAW) is made of a single medium-thick plate. First, stainless steel sheets are pressed into tube blanks in a die or forming machine. The LSAW pipe is produced by double-sided submerged arc welding and enlargement of its diameter. It has a wide range of product specifications, good toughness, plasticity, uniformity and compactness of the weld. Its advantages are large diameter, thick wall, high pressure resistance, low temperature corrosion resistance. In the construction of long-distance oil and gas pipelines with high strength, high toughness and high quality, the steel pipes needed are basically large diameter thick wall straight submerged arc welded pipes. According to API standard, in large oil and gas pipelines, when passing through the alpine zone, seabed, densely populated urban areas and other areas of category 1 and 2, the only designated applicable pipe type is the straight submerged arc welded pipe.