Flanges are critical in connecting pipes and valves in various industries, ranging from oil and gas to chemical processing. They provide a secure joint that is easy to assemble and disassemble when required. There are several types of Flanges, each designed to meet specific requirements. Swivel flanges and Lap Joint Flanges are two types that are commonly used in different applications. This blog post will explore the key differences between swivel and lap joint flanges regarding their design, function, and applications.

What is Swivel Flange?

A swivel flange is a type of pipe flange that allows for the rotation of the connected pipe. It is useful in applications where it is necessary to make mid-pipe turns and can also help reduce stress on piping systems by distributing weight more evenly. Swivel flanges are often used in industries such as oil and gas, water treatment, chemical, petrochemical and industrial gases. They are available in weld neck and slip-on designs with various size configurations ranging from 1/2”-24” diameter up to 24000 PSI rating.

What is Lap Joint Flange?

A Lap Joint Flange is a two-piece device that joins pipes in a piping system. It consists of a plain flange with an integrated ‘stub end’ that fits into the pipe and is attached to it via welding or other means. The stub end has radiused (curved) corners, which, when combined with the mating lap joint flange ring, allows more flexibility when connecting than traditional weld neck or slip-on flanges. This makes lap joint flanges ideal for applications where thermal expansion, such as operating at higher temperatures, could be an issue.

Difference Between Swivel Flange and Lap Joint Flange

Design and Function:

Swivel flanges are unique in allowing the mating flange to swivel freely around the inner ring, thereby eliminating potential misalignment. They are primarily used in applications requiring a high degree of flexibility. For instance, a swivel flange is often used in pipeline systems subjected to thermal expansion or contraction, where the pipeline sections need to move freely to prevent stress buildup.

On the other hand, lap joint flanges consist of two separate components, namely the stub end and the backing flange. The stub end is welded to the pipe’s end, while the backing flange provides the joint connection. They are designed to be bolted directly to the backing flange without directly touching the pipe end. This design allows the pipe sections to move freely within the system, reducing stress buildup.

Applications:

Swivel flanges are commonly used in offshore pipeline systems, particularly those subjected to high currents or deepwater conditions. They are also used in land-based pipeline systems where thermal expansion or contraction is a concern. In addition to pipeline systems, swivel flanges are used in other industrial equipment like heat exchangers, pumps, and tanks.

Lap joint flanges, on the other hand, are commonly used in applications where the piping system needs to be easily disassembled for maintenance or inspection. They are often used in low-pressure systems, where the joint is not subjected to significant forces. Lap joint flanges are also used in applications where the piping system’s material makeup requires dissimilar metals that are not weldable.

Materials:

Swivel flanges are typically made from forged or stainless steel alloys, depending on the application and working conditions. The inner ring of the flange is usually hydroformed to ensure a smooth, leak-free seal. Lap joint flanges are made from various materials, including carbon steel, stainless steel, and plastic. The choice of material depends on the application requirements, such as pressure and temperature.

Installation:

Swivel flanges are generally easier to install than lap joint flanges, mainly because of their design. Since swivel flanges can move around the inner ring, it allows for more flexibility during installation. When installing swivel flanges, it is important to ensure the gasket is seated correctly to prevent leaks.

Lap joint flanges require more work during installation since the stub end needs to be welded to the pipe beforehand. Once the stub end is welded, the backing flange is bolted to the stub end. A gap between the pipe and the backing flange allows for expansion and contraction.

Conclusion:

In summary, swivel flanges and lap joint flanges are two unique flanges commonly used in various industries. Swivel flanges provide flexibility and allow for free movement, making them ideal for pipeline systems subjected to thermal expansion or contraction. On the other hand, lap joint flanges provide an easy-to-disassemble joint connection for maintenance or inspection. They are commonly used in low-pressure systems or applications requiring dissimilar materials. Understanding the differences between these two types of flanges is important in choosing the right flange for your application.

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