Blind flange is a solid flange as shown below. The purpose of these is to block off a section of pipe or a nozzle on a vessel that is not used. (A nozzle is typically a pipe coming out of a vessel and is usually flanged so it can be connected to valves or piping). Many times a nozzle will be blanked off with a blind flange for pressure tests in a plant, or simply because the customer does not need all the nozzles that were supplied on the tank.
