What are Lap Joint Flanges?
Understanding lap joint flanges
A lap-joint flange is a two-segment gathering, with a stub end that has a lap-joint ring flange put over it. The stub end is then butt-welded to the line, and the flange ring can be pivoted to line up with the mating flange. This sort of flange connection is especially valuable for huge or difficult-to-change flanges.
Where are lap joint flanges used?
The lap-joint flange is primarily used in carbon or low alloy steel piping systems. Attachment of the lap-joint flange to the piping system requires a lap-joint stub end. The lap-joint flange and stub end assembly are used mainly in piping systems that necessitate frequent dismantling for inspection or routine maintenance. It is also used in the erection of large-diameter or hard-to-adjust piping configurations because of its quick bolt hole alignment.
The lap joint is a type of flanged joint as well as a type of facing. If lap joint flanges are considered for an application then the type and nature of the seal must also be considered.
Functioning and sealing methods for a lap joint flange
- The lap joint uses a separate flange to carry the bolting and apply the axial load. Lap joint connections can be considered when the piping material is exotic, expensive, or non-metallic. Exotic materials are very costly, so if the overall size of a component can be reduced, a considerable cost saving can be achieved.
- A lap joint flange can be connected to a flat face flange. This type of connection would occur at vessels or other components where the lap joint principle could not be applied.
- In theory, any of the common sealing methods could be applied to the lap joint flange face. If a metal-to-metal joint or plain gasket is proposed, then alignment may be a problem. In these cases, the alignment would be controlled by the bolting clearance and the clearance between the loose flange and the lap insert.
- The use of a ring joint would ensure good alignment. Alternatively, an extension of the “spigot and recess” principle, using the od of the lap insert, could be used to maintain good alignment.
- Lap joint flanges are shaped to accommodate the stub end. The combination of flange and stub end presents similar geometry to the raised face flange and can be used where severe bending stresses will not occur. The lap joint flange is economical if costly pipe such as stainless steel is used because the flange can be carbon steel, and only the lap joint stub end needs to be furnished in the line material.
- A stub end is used in a lap joint, and the cost of the two items must be considered. If both stub end and flanges are of the same material, they would be significantly more expensive than a weld neck flange.
Some of the important aspects of any type of flanges are flange bolting, flange fitting, flange dimensions, and flange weight.
Lap joint flanges fit over a line with a flared or stub end. This permits the flanges to turn unreservedly to effectively adjust bolt openings. These are ideal for frameworks whose plan/format may change or are often dismantled.
Flange fitting:
Lap joint line flanges slide straightforwardly absurd and are most usually utilized with stub end fittings. A line is generally welded to the Stub End and the Lap Joint line rib is allowed to pivot around the stub end. Flange fitting with lap joint flanges is easy and can be adapted with slight training.
Flange dimensions differ as per the applications. The required weight of the flange comes into consideration when planning the thickness of the flange.
Flange weight is an important aspect as flanges being in multiple quantities, contribute to the total weight of the component. Weight is directly related to cost reduction.
To conclude;
The pressure holding limit of lap joint flanges is relatively low. In any case, it is superior to that of slip-on flanges. The Lap Joint fills in as a backing ring on the stub. The principal benefit of the lap joint flange is that the jolt openings can be lined up with the matching flange after the welds have been finished.
