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, used to seal pipe openings. Its function is similar to that of a cap and pipe end, but the blind disk's sealing is a removable device, whereas the cap's sealing is not intended to be opened again. There are various types of sealing surfaces, including flat, convex, concave, tongue and groove, and annular connection surfaces. Materials include carbon steel, stainless steel, alloy steel, copper, aluminum, PVC, and PPR.