Orifice flange flange connection and general What is the difference?
Is to two pipes, fittings or equipment before each fixed at a flange on the flange between the two, together with flange pad, fastened together with bolts to complete the connection.

Orifice flanges are Orifice plate flow meter will be connected (orifice flowmeter measurement section) to the pipe, two flange fixed in the middle of the plate, through the flange on the pressure measuring points, diverted to the differential pressure transmitter on to measure the flow rate.