What Are Pipe Flanges?

Pipe flanges are disks used for the connection of a pipe system with various equipment and valves. It is the second most used method of joining pipes after welding. The pipe flanges are applied where the joints may later need dismantling for services such as maintenance. For a successful pipe connection using flanges, three components have to be available. They include the pipe flanges, the gasket, and the bolts. Although most of the flanges tend to be of stainless steel materials, they are also available in a wide range of materials to match the pipes’ materials for connection.

What Is A Socket Welded Flange?

Socket welded flanges are ideal to use for smaller pipe diameters in low-temperature and pressure scenarios. They are attached by inserting the pipe into the flange’s socket end and securing the connection by applying a single multi-pass fillet weld around the top. It allows for a better flow of the fluids inside the pipe. Socket welded flanges have high static strength but have a higher fatigue strength than a single, instead of double, fillet weld.

Types of Flanges

Threaded flanges

They are also known as screw flanges. Inside the flange bore, the flange has threads in which the matching male threads on the pipe will fit. Their presence makes it possible to have a successful connection without the use of welding. In some instances, small welds formed by the welders increase the strength of the link. The threaded flanges have their application in areas where low pressure and temperatures are involved. The pipes can transport fluids such as gases and water through areas where the threaded flanges are present. Threaded flanges are also a mandatory requirement in explosive areas, such as gas stations, as the execution of welded connections in such environments would be fatal.

Slip-on flanges

Slip-on flanges are easy to recognize due to their slim and compact shape. They come in a variety of sizes, which can accommodate systems with high flow rates and throughput. When establishing a connection, match the flange to the outer diameter intended for linking. After which, one shall need to use fillet welds on both sides to seal the relationship between the slip-on flanges and the pipe. Slip-on flanges are at times forged construction and fitted with a hub. When the slip-on has fabrications from plates and no extension on its neck provided, it will distort during welding. Hence it insists on machining to recover flatness.

Lap Joint Flanges

Lap joint flanges consist of two components, a stub end and a loose backing flange. They require the butt welding of the stub end of the pipe fitted with a backing flange to create the connection and is most effective in systems with limited physical space and frequent dismantling for inspection and cleaning. The use of lap joint flanges combined with stub ends is a cost-effective solution for stainless steel or nickel alloy pipelines. The lap joint flange material can be of a lower grade than the fabric of the stub end. The two main advantages of using the lap joints include the reduced overall cost of installing the flanges and the simplified bolting operations caused by the flange’s ability to rotate around the pipe to help with alignment.

Welding Neck Flanges

Weld Neck Flanges are of exceptionally high strength and require a single full penetration V-shaped butt welding for installation. They have a distinctive long conical hub, enhancing stability and reinforcement of the pipe to the flange. It is on this long-tapered hub that the flange connects to the pipeline. The tapered protrusion allows for the smooth distribution of the mechanical stress between the pipe and the flange. Due to their assured outstanding performance and integrity, these flanges are the best-used type of flanges in systems with multiple repeat bends and also those with high pressure and temperatures. Although their purchase cost is relatively higher, the welding cost for the flange is lesser.

Blind Flanges

Unlike other types of flanges, blind flanges do not have a center hole. They are used to seal a pipeline, a valve, or a pressure vessel and block the fluid flow. Best described as a boltable blank disc that forms a seal between two systems and can easily be removed by the users when needed. They have to withstand tremendous mechanical stress due to the system pressure and the required bolting forces. Besides the flanges being more comfortable to manufacture, Blind flanges are of average premium cost per kilogram than the other flange types.

 Specialty Flanges

These are a range of specialized flange types available to suit a range of uses and environments. They include:


It is a product manufactured by combining a welding neck flange with a forged nipolet. The nipoflange is a single solid piece of forged steel and not two different products welded together. Its primary use is branching pipelines at 90 degrees. In the installation, the nipolet part of the device connects to the run pipe. The flanged portion has bolts fastened on the flange of the branched pipe. Nipoflanges manufactured in the reinforced variant have additional mechanical strength than a standard nipoflange.


It is a combination of a weld neck flange and a weldolet. They are made out of a single piece and not by welding separate parts together.


Although a less common type of flange, Elboflange is a flange made from combining an elbolet with a flange. It branches a pipeline at 45 degrees.

Swivel Flange

Swivel flanges facilitate the bolt holes’ alignment between the two mating flanges, a feature helpful, especially when installing large diameter pipelines is involved. In the case of a large diameter pipeline, for instance, the pipe is fitted, at one end, with a standard welding neck flange and with a swivel flange at the other end. By simply rotating the swivel flange on the pipe, the operators can achieve a perfect alignment of the bolt holes in a more comfortable and faster way. Swivel flanges are available in all the standard shapes of flanges, including the socket welded flanges.

Expanding flanges

Also known as the expander flanges, they are used to increase the pipeline’s bore from a specific diameter to another .It is also used to connect other mechanical devices such as pumps and compressors with different inlet sizes. Specialists can use the expanding flange to increase the pipe bore only by one or a maximum of two sizes and not more. Expander flanges are cheaper and lighter than the combination of a buttweld reducer and a standard flange, which is the definitive solution for pipe bore increases above two sizes.

Reducing flanges

Also known as reducer flanges, they have an opposite function to the expander flanges. They are used to reduce the bore of a pipeline by one or two sizes. Otherwise, a solution based on the combination of a butt weld reducer and a standard flange is applied. They follow the same considerations regarding specifications, sizes, and material grades as the expander flanges.


An orifice is a disc-shaped flange engineered with a raised face. An orifice is used with orifice meters to measure the water, gas, or oil flow rate in the pipeline system.

Long weld neck

They are similar to weld neck flanges except that its neck is extended and acts as a boring extension. They have applications in high pressure and temperature environments. Their application being primarily in the gas, water, and oil processing industries in their pipeline systems.