Skip to content

Exploring the Varieties of Pipe Flanges

Pipe flanges help create a mechanical connection between two pipes or any pipe and a valve, tee, choke, or other equipment to establish a piping system. The procedure of connecting pipe flanges involves bolting, welding, or threading them together or attaching them to a piece of equipment,



which incorporates a gasket to ensure a secure seal. Flanges are the second most commonly employed method of joining piping systems, following welding.

Pipe Flanges- Types and Applications

Flanges offer versatility by enabling convenient assembly, disassembly, and accessibility to system components. A typical flange connection has three essential components mentioned below:

1. Flange 

2. Gasket 

3. Bolts or Welding hardware

Identification is present on the flange body

Proper identification of each piping component is achievable through marking. Flanges must be marked to enable easy tracing during fabrication and post-fabrication processes. 

The following information must be included in the marking of flanges.

1. Manufacturer logo

2. Material Grade

3. ASTM material code

4. Size

5. flange thickness (Schedule wall thickness with bevel)

6 Pressure-temperature class – service rating 

7. Heat No

8. Special marking if any W (Repair by welding) or QT (Quenched)

There exist eight main categories of pipe flange specifications, each catering to distinct or occasionally merged purposes:

Blind Flanges

Circular plates that are devoid of a center hole and used to seal off a pipeline, valve, or pressure vessel to prevent fluid flow are known as blind flanges. They are available in various sizes and materials and enable easy access to pipeline and pressure testing. 

Blind flanges  are appropriate for standard pipes of any size and can withstand higher pressure ratings than other flanges. They can endure significant mechanical stresses associated with high-pressure systems and the required bolting forces.

Lap Joint Flanges

In piping systems where regular maintenance or inspection is required, lap joint flanges are utilized. They are typically compatible with lapped pipe or lap joint stubs. These flanges are designed to slide over the pipe and rest on the back of the stub end, secured together by bolt pressure. 

The use of lap joint flanges offers two significant benefits. Firstly, the cost of the pipeline’s flanged joints is reduced due to their lower-grade material composition. Second, their design makes bolt alignment easier, resulting in less labor-intensive bolting operations.

Slip-On Flanges

Slip-on flanges have been engineered to be conveniently fitted over the piping’s end and then attached to the pipe or fittings by utilizing two filet welds – one inside and the other outside the flange cavity.

These flanges are best utilized in applications that require lower pressure. Furthermore, their installation process is simple and cost-effective. The bore diameter of slip-on flanges is larger than the pipe’s outer diameter, allowing the pipe to be inserted into the flange for welding purposes.

Socket Weld Flanges

In high-pressure piping applications, compact socket weld flanges are frequently utilized. These flanges are fastened to pipes, thus utilizing a solitary filet weld on the exterior part of the flange that distinguishes them from slip-on flanges that require two welds. 

Although they seem similar to slip-on flanges, socket weld flanges have a unique internal pocket design that creates a smooth bore, resulting in exceptional fluid flow. Socket weld flanges have a fatigue strength considered to be 50% greater than double-welded slip-on flanges, thanks to their single internal weld.

Threaded Flanges

Threaded flanges are quite popular in the industrial sector for their effortless installation without welding. They contain an internally threaded bore that aligns with the external threading on the pipe and is tapered to form a tight seal between the two as the tapers converge. 

Often, a seal weld accompanies the threads to reinforce and seal them further. Threaded flanges come in different sizes, materials, and flange weights, but they are only appropriate for low-pressure and small pipes and should not be utilized for high torques or large loads.

Weld Neck Flanges

Weld neck flanges are engineered for high-pressure, severe, and critical applications, featuring a long-tapered hub that can be welded to a pipe. Their tapered hub design effectively transfers stresses from the flange to the pipe thus providing superior strength reinforcement to counteract dishing. A single full penetration V-shaped butt weld connects the flange to the pipe. 

These heavy-duty flanges are perfect for extreme conditions such as high or sub-zero temperatures, pressure fluctuations, and handling hazardous and volatile fluids.

Reducing Flanges

Reducing flanges can be the perfect solution if you need to adjust the size of a pipeline. These devices are effective when you require a smaller bore size while keeping the same diameter.

However, it is significant to remember that reducing the size by one or two levels is the maximum recommended limit. If you need to modify the size further, it is best to use a combination of a butt weld reducer and a standard flange.

The dimensions of reducing flanges are almost identical to those of the larger pipe size, except for the bore and hub dimensions. Ultimately, reducing flanges are not only efficient but also very affordable when it comes to converting pipe sizes.

Orifice Flanges

Specialized applications necessitate the installation of orifice flanges, which are equipped with an orifice meter for the measurement of liquids and gases flowing through the pipeline at the point of the flange.

This method has the distinct advantage of featuring a pair of pressure “tappings” directly milled into the flange, avoiding the need for additional carriers or tappings within the pipe wall.

The Orifice Flange, offered with raised faces or Ring Type Joint (RTJ) facings, closely resembles a slip-on or weld neck flange, yet has the additional machining required. The governing specification is ASME B16.36 for these unions.

Why is it significant to securely Install Flanges Correctly?

It is essential to install and attach flanges according to their purpose. Anectodally, a story of an operator in Danville, Michigan… The worker was informed of an oil slick and strange smell on April 13th, 2011.

An estimated nine thousand barrels of petrol had escaped, one of which had reached the Bauer Drain. The gasket was not in place properly when the pipe was constructed in 2002, and the leak was the result of that misalignment.

It took five days to repair the pipeline, and the total cost of the clean-up was $35,728,903, out of which $20 million was dedicated to environmental remediation and the remainder to emergency response.

To guarantee top-quality products, each flange is scrutinized before dispatch from the factory. The inspection includes checking flange dimensions such as the outer and inner diameter of the body, the bolt circle and bolt hole diameter,

the hub diameter and the thickness of the weld end, the length of the hub, and the alignment of the bolt hole. ASME B16.5 and B16.47 standards define the permitted limits for these examinations.


0 0 votes
Article Rating
Notify of
Newest Most Voted
Inline Feedbacks
View all comments
8 months ago

Proper identification of piping components, including manufacturer logos and material grades, is essential for traceability during fabrication and post-fabrication processes.

8 months ago

Flanges play a crucial role in creating secure connections within piping systems, offering versatility through convenient assembly and disassembly.

8 months ago

What are the key components that must be included in the marking of flanges for proper identification? 

7 months ago
Reply to  Dean

Flanges should be marked with the manufacturer’s logo, material grade, ASTM material code, size, flange thickness, pressure-temperature class, heat number, and special markings like “W” for repair by welding or “QT” for quenched.

8 months ago

Why is proper installation of flanges so significant in piping systems? 

8 months ago
Reply to  Tracy

The correct installation of flanges is crucial to prevent incidents like the Danville, Michigan oil leak in 2011, where a misaligned gasket led to a significant environmental and financial cost.

8 months ago

The diverse types of flanges, such as blind, lap joint, slip-on, socket weld, threaded, weld neck, reducing, and orifice flanges, cater to specific applications and serve different purposes in piping systems.

Jeff B.
Jeff B.
7 months ago

Love that new folks to the flange industry could be completely trained on this site. Flange industry training for free.