Lap Joint Flanges: How and When to Use Them

Flanges play a crucial role in piping systems, but not every flange fits every situation. For setups requiring flexibility, easy alignment, and cost efficiency, lap joint flanges are often the perfect fit. But how do you know if they’re the right choice for your project?

In this article, we’ll break down how lap joint flanges work, why they’re unique, and the specific scenarios where they can make a big difference. If you’re curious about where these flanges shine and how they compare to plate flanges and other types, you’re in the right place.

What Are Lap Joint Flanges?

What are lap joint flanges? Lap joint flanges are two-part flanges consisting of a stub end and a ring-shaped flange that fits loosely over it. 

The flange itself is not welded to the pipe but is used to hold the stub end in place. The design allows for easy alignment and rotation, making them highly versatile. The stub end is welded to the pipe, and the lap joint flange can be freely rotated around the stub end. This makes aligning bolt holes during assembly much easier.

Lap joint flanges are particularly useful in systems where frequent disassembly or adjustments are required, providing a great alternative to more rigid options like plate flanges.

Advantages of Lap Joint Flanges

Easy Bolt Alignment

One of the standout features of lap joint flanges is their ability to rotate around the stub end. Unlike fixed flanges, where aligning bolt holes can be tricky, lap joint flanges make it easy to position bolts without having to adjust the pipe or the entire assembly. This results in quicker installation and less stress on the piping system.

Reduced Material Costs

In many applications, the backing flange of a lap joint does not come into contact with the process fluid. This means you can opt for a more cost-effective material for the backing flange while using a corrosion-resistant or high-strength material for the stub end. This approach can result in significant savings, particularly in large-scale projects or systems with expensive materials like stainless steel.

Perfect for Frequent Disassembly

If you anticipate the need to take apart and reassemble your piping system often, lap joint flanges are an excellent choice. Since the flange can be easily rotated and is not permanently welded to the pipe, disassembly is straightforward. This makes lap joint flanges popular in systems that require frequent cleaning, inspection, or maintenance.

Less Stress on Piping

The lap joint flange’s loose design helps absorb movement in the piping system. Because the flange is not rigidly fixed, it can better tolerate the natural vibrations, thermal expansions, and contractions that often occur in pipes. This can reduce stress on the weld joint and the pipe, helping to extend the system’s overall lifespan.

Common Uses for Lap Joint Flanges

Lap joint flanges are highly versatile and can be used in various settings. However, they excel in specific situations where their unique features bring the most benefit:

Low-Pressure and Low-Temperature Systems

Lap joint flanges are best suited for low-pressure and low-temperature applications. They are not designed to withstand the extreme conditions that some other flanges, like weld neck or plate flanges, can handle. Therefore, you’ll commonly see lap joint flanges in systems where operating conditions are moderate and flexibility is more important than high-pressure endurance.

Example:

Cooling water systems, air piping, and non-critical process lines in industrial setups are all environments where lap joint flanges can be a perfect fit.

Systems Requiring Flexibility and Adjustment

In systems where pipes need to be realigned or components regularly replaced, lap joint flanges make the process much easier. Since the flange can rotate freely, you can quickly align bolt holes and make adjustments without cutting, grinding, or re-welding any parts.

Example:

For systems like fire protection piping or temporary construction setups, where layout changes are frequent, lap joint flanges offer a hassle-free way to modify connections.

Corrosive or Specialty Material Environments

When piping needs to be corrosion-resistant or made from specialty materials like stainless steel or titanium, costs can add up quickly. By using a lap joint flange setup, you can make the stub end from the required specialty material while using a lower-cost flange material, optimizing both cost and performance.

Example:

In a marine environment, where the piping must resist saltwater corrosion, a stainless-steel stub end paired with a carbon steel lap joint flange can be a cost-efficient solution.

Systems Exposed to Vibration and Thermal Expansion

Piping systems that experience movement—whether from vibrations, temperature changes, or pressure variations—benefit from the flexibility of lap joint flanges. Since these flanges are not welded directly to the pipe, they allow for some movement, reducing stress on the connection and avoiding issues like cracking or warping.

Example:

Steam systems, exhaust lines, and systems exposed to fluctuating temperatures use lap joint flanges to accommodate expansion and contraction without damaging the connection.

When to Choose Lap Joint Flanges Over Plate Flanges

While plate flanges are widely used for general-purpose piping systems, lap joint flanges come into play when flexibility, ease of alignment, and cost efficiency are top priorities. If your system requires frequent adjustments, uses costly materials, or operates in a low-pressure environment, lap joint flanges may be the more suitable choice. 

On the other hand, if the system needs to handle high pressure or doesn’t require regular maintenance, plate flanges or other welded options might be more appropriate.

Ready to Get Started with Lap Joint Flanges?

For top-quality lap joint flanges that are both reliable and cost-effective, look no further than Long’an Flange. With over 13 years of experience in producing high-performance flanges, we are committed to meeting your piping needs. 

Discover our stainless steel lap joint flanges and see how they can benefit your next project!

FAQ Section

What is the difference between a lap joint flange and a slip-on flange?
A lap joint flange uses a stub end to attach to the pipe, allowing the flange to rotate freely. A slip-on flange, on the other hand, slides over the pipe and is welded directly.

Can lap joint flanges be used for high-pressure systems?
No, lap joint flanges are best suited for low-pressure and low-temperature environments. For high-pressure systems, welded flanges like weld neck or plate flanges are recommended.

What materials are lap joint flanges made from?
They can be made from various materials, including carbon steel, stainless steel, and specialty alloys, depending on the system’s requirements and conditions.

How do you install a lap joint flange?
The stub end is welded to the pipe, and the lap joint flange fits loosely over the stub end. Once the pipe sections are aligned, the flange is bolted together with the mating flange.

Resources:

Lap Joint Flange

When To Use Lap Joint Flange: A Practical Guide

The advantages of Lap Joint Flanges

Understanding Lap Joint Flanges: Applications and Advantages