There are two kinds of welding technology used in the production of ERW steel pipe, including induction welding and contact welding. The ERW steel pipe applied wide hot rolling steel profile as raw material, and went through pre-bending, continuous forming, welding, straightening, cutting and other processes. So the ERW steel pipe has short weld joints, high dimensional accuracy, uniform thickness, and excellent surface and can bear high pressure. However, it also has shortcomings, small diameter and thin wall, and the weld joints are easy to be eroded. Currently, ERW steel pipe are mainly used to transport gas as well as oil to city residents.
Compared with the process of SSAW steel pipe, the process of ERW steel pipe has advantages of high dimensional accuracy, uniform thickness, surface quality. But the drawback of ERW steel pipe is that it only has small and medium-caliber thin-walled tube, and welding is easy to produce gray leaf spot. So ERW steel pipe is more widely used in areas of city gas, crude oil transportation.
LSAW steel pipe use single plate steel as raw material, applied double-sided submerged arc welding. The finished products have larger specifications and the welding joints have excellent ductility, plasticity and good sealing. LSAW pipes have large diameter, thick wall and can withstand high pressure and low temperature. LSAW pipes play a major role in oil and gas pipelines with features of high strength, high quality and long distance. According to the standard of American Petroleum Institute (API), the LSAW pipe is the only designated pipe in large scaled oil and gas transportation, especially when the pipelines cross the densely populated urban areas and the first and second class cities.
Spiral submerged arc welded (SSAW) pipes has spiral welding joints and the pipes are welded and formed at the same time. The strip steel with the same specification can produce SSAW pipes with various diameters. The welding joints can avoid major stress and have better force resistance. Disadvantages of SSAW steel pipe are poor geometrical diameters, longer welding joints and joints are easily to have cracks, porosity and other welding defects. According to the design specification of oil and gas pipeline. SSAW pipes only can be used in the third and fourth class areas. Developed countries have improved the technology, apart forming and welding, and have pre-welding and precise welding processes which make the quality of welding close to UOE pipes.
