lapjointfläns

Lap joint flange is a two-piece flange arrangement used in piping systems. It consists of a stub end that is welded to the pipe and a loose lap joint flange that slides over the stub end. When assembled, the lap joint flange is bolted to a mating flange and a gasket sits between the faces of the two flanges to form the seal. The key feature is that the lap joint flange can rotate around the stub end, allowing easy alignment of bolt holes and straightforward replacement of flanges without cutting or rewelding the pipe.

In operation, the pressure boundary is provided by the welded stub end and the piping, while the lap joint flange mainly serves to provide a bolted connection and a seal with the mating flange. The gasket seals between the lap joint flange and the mating flange, not between the stub end and the lap joint flange. This design facilitates maintenance, inspection, and material changes, particularly in large-diameter or heavily serviced lines.

Advantages of lap joint flanges include easy alignment during assembly, the ability to replace flanges without disturbing the pipe, and compatibility with different materials on the flange side while keeping the pipe material fixed. They are commonly used in corrosive or expensive piping systems and in applications requiring frequent disassembly.

Materials and sizes follow standard flange practices, with lap joint flanges available in carbon steel, stainless steel, and various alloys, across a range of DIN/ANSI pressure classes and bore sizes. See also standard flanges and piping flange assemblies for related concepts.