Applications And Uses Of Lap Joint Flanges

By Author: Jeeten Gupta
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A Lap Joint Flange also knew as a loose flange is a two-piece device that is similar to a weld-neck flange used in carbon or low alloy steel piping systems.
In Simple words, a lap-joint flange is a two-component assembly, with a stub end that has a lap-joint ring flange placed over it. The stub end is then butt-welded to the pipe, and the flange ring can be rotated to align with the mating flange.
The thickness of the hub is normally about ¼” to 3/8″ inches. The back face of this flange has a hub that has a rounded transition that joins the hub to the sleeve. Lap joint pipe flanges slide directly over the pipe and are most commonly used with stub end fittings. A pipe is usually welded to the Stub End and the Lap Joint pipe flange is free to rotate around the stub end. The benefit of this is that there will not be any issues with bolt hole alignment. Lap Joint pipe flanges are often used for applications that require frequent dismantling.
 
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... Materials used for making a lap Joint Flange:

Carbon Steel
Alloy Steel
Stainless Steel
Cast Iron
Brass
Aluminum
Bronze
Pvc etc.

 
Advantages of Lap Joint Flanges:

Lap Joint Flange Allows Rotational Alignment Capability.
Lap Joints Flange has the freedom to swivel around the pipe.
Bolt Holes can be aligned with the flange even after the weld has been completed.
Assemble and Disassemble of a Lap Joint Flange is better than Slip-on Flange
Pressure holding capacity of a lap joint Flange is better than Slip on Flanges.
Lap Joint Flanges Can be reused when exposed to corrosion.
Contact with the fluid inside the pipe provides greater durability of this flange.
Lap Joint Flange works as a backing ring on the stub

 
Disadvantages of Lap Joint Flanges:

Cannot Withstand High Pressure but is able to understand Low pressure
Lap joint Flanges are mainly used in Low-Pressure Applications
Sealing Requirements of a Lap joint flange is not High
The Strength of the weld ring is low.

 
DIMENSIONS AND SPECIFICATIONS OF LAP JOINT FLANGES IS SHOWN IN THIS ARTICLE

When to use Lap Joint Flanges:

Now that we know what a lap joint flange is let us now understand when to use a lap joint flange.
As we know that a Lap Joint Flange is a two-piece device that is much like a weld-neck flange but also as a loose slip-on flange. One piece is a sleeve called a 'Stub-end" and is shaped like a short piece of pipe with a weld bevel on one end and a narrow shoulder on the other end called the hub. The hub is the same outside diameter as the raised face (gasket contact surface) of a weld neck flange. The thickness of the hub is normally about ¼" to 3/8". The back face of the hub has a rounded transition (or inside fillet) that joins the hub to the sleeve.

The other piece of a Lap Joint Flange is the backing flange. This flange has all the same common dimensions (O.D., bolt circle, bolt hole size, etc.) as any other flange however it does not have a raised face. One side, the backside, has a slight shoulder that is square cut at the center or pipe hole. The front side has a flat face and at the center hole an outside fillet to match the fillet of the "Stub-end" piece. The flange part of the Lap-joint flange assembly is slipped on to the stub-end prior to the sleeve being welded to the adjoining pipe or fitting. The flange itself is not welded or fixed in any way. It is free to spin for proper alignment with whatever it is joining to.

The "Stub-end" can normally be purchased in two lengths. There is a short version, about 3" long and a long version of about 6" long. It is prudent for the piping designer to know which version is in the piping specification.

Because of its two-piece configuration, the Lap Joint Flange offers a way to cut costs or simplify work. The cost-saving comes when the piping system requires a high-cost alloy for all "wetted" parts to reduce corrosion. The sleeve or Stub-end can be the required higher cost alloy but the flange can be the lower cost forged carbon steel.

The work simplification comes into the picture where there are cases that require frequent and rapid disassemble and assembly during the operation of a plant. The ability to spin that backing flange compensates for the misalignment of the bolt holes during reassembly.
 
Common Application and Uses of Lap Joint Flange:

Lap Joint Flange uses in Pipeline engineering
Lap Joint Flange uses in Oil & gas industry
Lap Joint Flange uses in Mechanical engineering
Lap Joint Flange uses in Plant engineering
Lap Joint Flange uses in the Marine industry
Lap Joint Flange uses in Wastewater management
Lap Joint Flange uses in the Chemical industry
Lap Joint Flange uses in the Petrochemical industry
Lap Joint Flange uses in the Power industry
Lap Joint Flange uses in Aerospace Industry
Lap Joint Flange uses in the Food processing industry and many more.

 
Quick Links:

An Overview of Weld Neck Flanges
When to Use Slip-on Flanges
Applications and Use of Threaded Flanges