A guide to flanges

Understand more about flanges, flange design and flange faces in our guide:

• Different types of pipe flanges
• Flange types: at a glance
• What is flange facing?
• Face flanges: at a glance
• Protecting flanges
• Flange materials
• Gasket materials
• Flange sizes

At Essentra, we sell a range of pipe and flange protection to support your applications. Our expert guides can also help you choose the right solution for your project:

How you make a pipe-flange connection varies. It depends on the type and the requirements of your piping system. Some are weld-on pipe flange, while others can be screwed on. The type of flange you choose will also depend on issues such as pressure capacity and application. But first, let’s look at common flange types.

Different types of pipe flanges

While specialty pipe flanges are available, there are six main types. Here they are, along with how to secure the flange on a pipe.

Flange types: at a glance

What is flange facing?

Flanges with different faces should not be mated. For example, a raised face to flat-face flange connection will result in leakage from the joint, per ASME code B31.3.

Raised face flanges

The most common type is the raised face flange. Its name comes from the raised gasket surface, above the bolting circle face. The raised face concentrates more pressure on a smaller gasket area. In turn, this increases the joint’s pressure containment capability.

The height of the raised face is determined by the flange’s pressure rating. Likewise, the higher the pressure rating, the bigger the flange diameter, the more bolts needed and the thicker the flange.

Flat face flange

Raised face vs. flat face flange, also called full face flange, isn’t an issue. They play different roles. Instead of a raised face, this is a flat surface. Consequently, the gasket surface is the same plane as the bolt frame, covering the flange from its inside diameter to outside diameter.

• Full face is designed to avoid the bending that flanges undergo as bolts are torqued.
• Cast iron can break during this process, which is why this material is often used to make flat face flanges. The design prevents this problem from happening.

Ring-type-joint face flange

High temperature, high-pressure flanges or rather, flanges used in extreme environments, utilize a ring-type-joint face. These flanges often have a raised face with a ring groove machined into it. They can also have grooves cut into their faces with steel ring gaskets. The flanges seal when the bolts are torqued, compressing the gasket between the flanges into the grooves.

Ring joint flange vs raised face

The purpose behind a raised face flange is to concentrate more pressure on a smaller gasket area, increasing the joint’s ability to contain the pressure. Ring-type-joint face flanges don’t use gaskets. The groove within the flange enables the ring to center itself when the bolts are torqued. As the process pressure increases, so, too, does the sealing pressure.

Face flanges: at a glance

Protecting flanges

View our range of flange covers

Flange materials

Whether steel pipe flanges or a plastic flange, you should base the material you choose on its application. Typically, the materials should match your pipe material, but again, it depends on your application. For example, if your piping system is used for air or other non-corrosive applications, then your flanges and pipes may not need to be of the same corrosion-resistant material as acidic or caustic liquids.

Otherwise, if you’re interested in say, carbon steel slip-on flanges, you need to match the grade steel you choose to the pipe. Common flange materials include:

Carbon steel

Carbon-steel flanges are alloyed primarily with carbon. Carbon steel has a high hardness and strength that increases with carbon content but lowers ductility and melting point. Carbon steels range from mild and low, with 0.16—0.29% carbon to ultra-high carbon steel, with around 1–2% carbon. Steels with carbon content above 2% are considered cast iron.

Alloy steel

Just as you can enhance properties in plastics with additives, you can alloy steels with other elements to enhance the properties of your chose steel. Common alloys include molybdenum and chromium. Through different elements, you can increase a steel’s strength, ductility, corrosion resistance, and machinability.

Stainless steel

Stainless steel is alloyed with chromium in amounts above 10%. It’s chromium that gives stainless steel a higher corrosion resistance than carbon steel, which easily oxidizes from air and moisture exposure. Stainless steel is ideal for corrosive applications that also require high strength. Different grades of stainless steels yield different outcomes. You can learn more in our guide, Understanding stainless-steel grades.

Cast iron

When iron is alloyed with carbon, silicon, and other alloyants, the result is cast iron. Cast irons have good fluidity, castability, machinability, and wear resistance. They tend to be brittle to a degree with low melting points.

Aluminum

This is a low-density metal with medium strength. Malleable and ductile, it’s more corrosion resistant than typical carbon and alloy steels. Aluminum is suitable for flanges that need both strength and low weight, such as for irrigation applications.

PVC

A PVC flange is low cost and durable. PVC pipe flanges also have the advantage of being both chemical and corrosion resistant. Additives can make PVC more flexible and softer. PVC flange connections can provide extra protection to underlying pipes. They’re also popular for water-treatment processes, favored by the agricultural industry and used in domestic plumbing. Lightweight and easy to install, PVC flanges are perfect for PVC pipe systems.

Gasket materials

For all flange types excluding ring-type-joint faces, you’ll need gaskets. Choose them based on factors such as operating temperature, the fluid being conveyed by the pipeline, flange type, size, pressure class or rating and other specifications. First, however, you need to know material properties, which can be enhanced with additives.

Flange sizes

Flange dimensions are determined by the nominal pipe size (NPS) and the pressure class that your application requires. The higher the pressure rating of the class, the higher the size and dimensions of the flange. Typically, a 1/2" pipe flange will belong to the 150-pound pressure class. For threaded flange, a 4" pipe flange is the largest size available.

Large diameter flanges are in higher pressure classes. Below are the different classes:

Pressure classes

• 150 lbs
• 300 lbs
• 400 lbs
• 600 lbs
• 900 lbs
• 1500 lbs
• 2500 lbs

Size standards

Flange types and sizes vary, but they’re manufactured according to the standards set by organizations. For example, a long weld neck flange ASME B16.5 conforms to ASME standards, and might differ slightly from another standard. ASME B16.5 swivel flange dimensions – a type of weld neck flange – have equivalents in EN and MSS standards.

(If you see, for example, ANSI 150 swivel flange dimensions, this is incorrect. ANSI at one time published standards and started working with ASME in 1988. At the time standards appeared as ANSI/ASME, but by 1996, ASME had taken over standards.)

So your first task is determining the standard you’ll work to, which will likely follow what’s commonly used in your area.

Size standards are set according for each pressure class.

The example here is a threaded flange, both raised face and flat face, according to ASME B16.5. The pressure class is 150.

Sizes: inches

EN sizes: millimetres

Download free CADs and try before you buy

Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen the right product for what you need. 

If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.

Whatever your requirements, you can depend on fast dispatch. Request your free samples or download free CADs now.

Questions?

Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.