At Chemipetro we manufacture a wide range of pipe fittings and pipe flanges, and it is important that the specifier selects the correct type of fitting for the correct application.

An example of this is a lap joint flange. These consist of a normal circular flange plate with the usual bolting holes. Unlike a weld neck flange, where the central hole is the same size as the pipe and is designed to be welded onto the end of the pipe, the central hole of a lap joint flange is the size of the outside diameter of the pipe, and the flange is designed to slip onto the pipe. To fit the lap joint flange a lap joint stub has to be welded onto the end of the pipe which has a collar to stop the lap joint flange from coming off. So far, apart from a slightly different installation method there would seem to be little difference between the two types of flanges.

However the cost of the lap joint flange together with the lap joint stub is approximately one third higher than a weld neck flange. In addition the pressure holding ability is significantly less than a comparable weld neck flange and its fatigue life is approximately one tenth. So why would you use a lap joint flange?

The answer is flexibility. Like a ring neck flange, the collar can rotate, allowing flange plates to be more easily aligned which is especially useful on large diameter pipes. They are also easy to dismantle so making them suitable for situations which have a high maintenance requirement or need regular inspecting.