Abstract: Described in the article are all about the R & D and application of the medium-sized COE double SAWL pipe, involving such aspects as technological design and equipment configuration of the operation line, formation theory and the inner/outer submerged arc welding process, and how pipes of this type are being used in domestic pipeline projects.Relevant physicochemical tests and actual application practices demonstrate that the medium-sized COE double SAWL pipes are in possession of good profile, excellent weld seam quality and consistent general product quality, being capable of replacing HFW pipes with sizes under Φ508 mm as well as part of the seamless steel pipes and SAWH pipes, and suiting for a wide range of uses, and having an encouraging development potential.