Flange cover, also called blind flange, is a flange without a hole in the middle, used to seal the pipe plug. There are many types of sealing surfaces, including flat, convex, concave-convex, tongue and groove, and ring connection surfaces.
Sealing surface: flat surface (FF), raised surface (RF), concave and convex surface (MFM), tongue and groove surface (TG), ring connection surface (RJ)