First piece of the lap joint flange is a sleeve called a ‘Stub-end” and is shaped like a short piece of pipe with a narrow shoulder on one end and a butt weld end on the other end which called the hub. The narrow shoulder dimensions is like the rase face of the flange, the butt weld end of the stub-end is like the neck of the weld neck flange, the diameter and thickness is according to the pipe for connection. The back face of the hub has a rounded transition that joins the hub to the sleeve. 

The other piece of a Lap Joint Flange is the backing flange. Backing flange dimensions are same with other common flanges (O.D. ,PCD, Bolt hole, etc.) , however it does not have a raised face (the stub end has the raised face ).On One side of the lap joint flange, the backside, has a slight shoulder that is square cut at the center or pipe hole. The front side has flat face and at the center hole an outside fillet to match the fillet of the “Stub-end” piece. The flange part of the Lap-joint flange assembly is slipped on to the stub-end prior to the sleeve being welded to the pipe or fitting for connection. The flange itself is not welded or fixed in any way. It is free to spin for proper alignment with what ever it is joining to. 

The Lap joint flanges are used a lot in the low pressure piping systems ,haihao flange factory can produce the lap joint flanges as per request , help clients to reduce the cost and solve the application problems