Blind disk is formally known as Flange cover, sometimes also referred to as a blind flange or pipe plug. It is a flange without a hole in the middle, used to seal pipe openings. The function it serves is similar to that of a cap or pipe end, but the blind disk seal is a removable sealing device, whereas the seal of a cap is not intended to be opened again. There are various types of sealing surfaces, including flat, convex, concave, tenon-and-groove, and annular connection surfaces. Materials include carbon steel, stainless steel, alloy steel, copper, aluminum, PVC, and PPR.