Lap Joint Flanges are a less requested type of flange with an extended hub and a machined radius at the base of the flat face. This curved radius allows for the placement of a pipe fitting known as a stub end.
This type of flange is made to saddle over stub end fitting for rotation. The pair are an excellent choice for situations which require a constant removal and reinstallation in order to inspect the connection. This combination allows for the rotation of the lap joint over the stub end for accurate bolting.
Lap joint flange with a stub end and the radius on the face, below:
The hubs are typically taller than a slip on style and can be modified per your requirements. Slip ons in higher pressure classes are often made with the height of a lap joint for a better connection. If the hub height is not a concern and a lap joint is not readily available, customers will sometimes opt for a slip on made to a lap joint style with a machined hub.
Often times, a stub end will be made of a special material grade (nickel alloy), with the lap joint consisting of basic carbon or commodity stainless, in order to reduce the overall cost of the connection. Naturally, we recommend that both items are of the same grade for the purposes of uniformity, but your application will determine what’s best and/or necessary.
Typical lap joint flange dimensions: