Classification of stainless steel flanges Pipes Flange can be divided into five basic types according to the connection with the pipe: flat welding flange, butt flange, thread flange, socket welding flange, loose flange. (RF), concave (FM), concavo-convex (MFM), tongue and groove (TG), full plane (FF), and ring connection (RJ) are commonly used. Welded steel flange welded steel flange for the flange and pipe counterpart welding, its structure is reasonable, strong and stiffness, can withstand high temperature and pressure and repeated bending and temperature fluctuations, sealing and reliable, nominal pressure of 0.25 ~ 2.5MPa of the welding flange with concave and convex sealing surface.