Joint flanges are used on piping fitted with with lapped pipe or with
lap joint stub ends. The lap joint flange with the stub end assembly are
normally used in systems requiring frequent dismantling for inspection
and cleaning and where the ability to swivel flanges and to align bolt
holes materially eases the erection of large diameter or unusually stiff
piping. These flanges are also used in applications where there is a
need to facilitate bolt alignment.
These type of flanges are similar to slip-on flanges. The only
difference is that it has a curved radius at the bore and face to
accommodate a lap joint stub end. They may be used at all pressures and
are available in a full size range. These lap joint flanges slip over
the pipe, and are not welded. They are otherwise fastened to it. Here
the bolting pressure is transferred to the gasket by the pressure of the
flange against the back of the pipe lap.
Certain factors to consider are as follows:
- Design Standard
- Normal Pressure
- Face Type
- Corrosion Resistant
- Carbon steel
- Stainless steel
- Alloy steel
- Cast Iron
- PVC etc.
Advantages of Lap Joint Flanges:
- Recommended in applications that require frequent dismantling of
the flanges and pipe.
- Used with a matching stub-end insert.
- Can rotate to allow for an easy alignment of bolt holes.
- Not recommended in extreme or high-pressure temperature
Lap Joint flanges have certain special advantages over other flanges.
These are as follows:
- Lap Joint flanges have the freedom to swivel around the pipe.
This facilitates the lining up of opposing flange bolt holes.
- Lack of contact with the fluid inside the pipe leads to the
greater durability of these flanges.
- In piping systems which corrode or erode quickly, the lap joint
flanges may be salvaged for re-use.
- The pressure-holding capacity of lap joint flanges is little. But
it is better than that of slip-on flanges.
- The Lap Joint works as a backing ring on the stub.
- The main advantage of lap joint flange is that the bolt holes can
be aligned with the matching flange after the welds have been
- They allow rotational alignment capability.