It is made by rolling low-carbon carbon structural steel or low-alloy structural steel strip according to a certain spiral angle (called forming angle) into a tube blank, and then welding the tube seam together. It can be made with a narrower Strip steel produces large diameter steel pipes. Its specifications are expressed by outer diameter * wall thickness, and the welded pipe shall be ensured that the hydraulic test, the tensile strength of the weld and the cold bending performance must meet the requirements.