Welded flange is interface end diameter and wall thickness and welding pipe, pipe welding on two. Flange interface is slightly larger than the outer diameter machining a concave point, pipe inside welding. The welding performance of the butt welding is better, and the corrosion is small. Welding and butt welding is the welding flange and pipeline connection, flange welding only one side welding without welding pipe and flange connection inside the mouth, butt welding flange welding installation requires double welding flange. So the flange generally used for low and medium pressure pipeline, welded flange for connection, high pressure pipe, butt welding flange is at least PN2.5MPa, use the welding in order to reduce the stress concentration of welded flange general is also called the nipple flange neck flange. Installation welding flange so that the labor cost and material fee is high, because the more a process. Welded flange not all need inside and outside the double welding, not only the general outside welding a special requirements, have not seen 1/2 "), flat welding flange: it is better for welding, because the pipe and flange of the vertical pipe, not inclined.