The Main Types of Pipe Flanges to Know
It’s ideal to know the different types of pipe flanges in order to know what’s best for your engineering needs. Learn everything you need to know below.
Pipe flanges are circular-shaped piping components that attach pipes to connect or block other components like nozzles, valves, special items, etc. After welding, these are the second-most-popular joining method in the Engineering universe.
Piping-flanged joints are most preferred wherever dismantling of components is required for inspection, maintenance, operational purposes, or replacement. Pipe flanges also use gaskets and bolts in between to ensure piping joints are leakage-free.
A pipe flange is selected based on pipe class – which follows ASME B 16.47 or ASME B 16.5 – and pressure-temperature rating. Nevertheless, it is possible to manufacture custom-made pipe flanges, though it is not preferred in the industry. Pipe flanges remain the best alternative to threading or welding and are generally manufactured by forging.
Types of Flanges
Numerous types are presently used in the industry. They are usually classified based on the following:
- Pipe attachment/connection
- Pressure-temperature rating
- Flange Facing
Pipe Flange Types: Based on Pipe Attachment/Connection
Weld Neck Flanges
These are highly suitable for high pressure and temperature applications. The neck of a pipe flange is usually welded to the neck of the pipe.
The significant features are as follows:
- There isn’t any flow restriction since the Pipe ID and Flange ID match. Turbulence and erosion are also done away with.
- Weld neck pipe flanges come with a long and tapered hub between the weld joint and flange ring. This is why these flanges are sometimes known as ‘high hub flanges.’
This hub provides a gradual transition right from the flange ring thickness to the pipe wall thickness. The ID also needs to match with the pipe ID. The smooth transition significantly increases the flange’s strength and minimizes high-stress concentrations.
- This particular type of flange is usually attached to the pipe via butt welding. It can also be radiographed if this is a vital requirement.
- Weld neck pipe flanges are usually suitable for extreme service conditions. This is an intentional design so that the pipe flanges can withstand repeated bending from contraction, line expansion, or any other external force.
- Weld neck pipe flanges are generally considered the best-designed butt welded flange ever in the industry. The welding area prevents undue distortion since it is away from the face.
- The Weld neck pipe flange needs to be aligned accurately to bolt holes before welding commences.
- Weld neck pipe flanges are generally much more expensive than other flange types.
- It is highly essential to provide the Pipe Schedule number and ID while ordering weld neck flanges.
Lap Joint Flanges
Lap joint flanges are essentially a 2-component assembly. They come in backing lap-joint ring flanges, and stub ends. Pipes are butt-welded to the stub end, leaving the lap joint free to rotate around the stub end. The stub end’s face acts just like a raised face of the flange, though it can be made of different materials to save costs. The stub end is the only part that comes in direct contact with the fluid.
Slip-on pipe flanges are generally shorter than weld neck flanges. This means that they can be used where there is a constraint over space. The inside diameter of the slip-on pipe flanges is somewhat larger than the outer diameter of the pipe. And this makes it easy to slide over the pipe.
Slip-on flanges can be secured to the pipe via the use of 2 fillet welds from inside and outside. These are widely used in lower pressure and temperature applications due to their low initial cost. In most cases, their lifespan is approximately 1/3 (one-third) that of the weld neck flange.
Here are some of the significant features:
- Slip-on flanges are not recommended for any critical or corrosive services.
- The overall strength of the slip-on pipe flange is about 2/3 that of a comparable welding neck flange.
- Slip-on pipe flanges are not too suitable for cyclic loading services.
- The joint in a slip-on pipe flange can’t be subjected to radiography due to the absence of a full penetration weld.
Socket Weld Flange
Socket weld pipe flanges make use of a single fillet weld on the exterior of the flange. Pipes are inserted in sockets at the start – in a socket weld flange connection – until it eventually reaches the flange bottom. It is then lifted by 1.6mm and fillet welded at last. That 1.6mm gap is put in place to give room for proper pipe positioning within the flange socket after the weld’s solidification.
Socket Weld Flanges are highly suitable for small pipes – of up to 2 inches – and not recommended or ideal for severe services. However, they can be used for high-pressure piping that doesn’t transfer corrosive fluids. This is because the accumulation of fluid within the gap can quickly corrode the pipe. Socket weld pipe flanges are highly comparable to slip-on flanges.
Blind pipe flanges are solid. They do not come with central holes used for blocking off one section of pipe or nozzle on unused equipment. They are usually designed to powerfully withstand extensive pressure stress.
But then, blind pipe flanges do not need to absorb too much thermal stress since they can always expand. This is because they are already attached to the very end of the piping connection.
Bling pipe flanges – which can be Raised Face or Flat type – usually weigh much more than other pipe flanges. They are commonly used when pressure-testing piping systems.
Screwed or Threaded Flange
Screwed or threaded pipe flanges are joined to pipes by screwing them in. They are generally used on piping systems that disallow direct welding on the pipe. Threaded pipe flanges are used for Galvanized Piping.
Industrial threaded or screwed pipe flanges are made in different sizes of up to 4 inches with numerous pressure ratings. They are only used for small pipes that convey low-pressure-temperature fluids.
Threaded pipe flanges are commonly used in areas that contain explosives. Threaded flanges are used on somewhat thicker pipes since cutting threads on very thin pipes is extremely difficult.
The significant features of threaded flanges include:
- The attachment process is pretty quick
- The threads have a tendency to leak under cyclic loading. This is why they are not recommended for cyclic services.
- Pipe Flange Types: Based on Flange Facing
- These flanges are classified as follows: Raised Face Flanges, Flat Face Flanges, Tongue and Groove, Ring Type Joint Flanges, and Male and Female.
Pipe Flange Types: Based on Pressure-Temperature Rating
Pressure-temperature rating flanges are classified as follows:
When the pressure rating increases, the flange strength, load-carrying capacity, and dimensions also increase.
Pipe Flange Types: Based on Governing Design Code
Categorized based on governing design code:
- DIN flanges
- BS Flanges (BS 10, BS 1560)
- Custom made flanges
- ASME/ANSI Flanges (ASME B16.1, ASME B16.5, ASME B16.42, ASME B16.47)
- API flanges (API 6A, API17D), etc.
Furthermore, they can be categorized as follows, based on the pipe flange material of construction:
- Cast Iron Flanges
- Carbon Steel Flanges
- Ductile Iron Flanges
- Alloy Steel Flanges
- SS/DSS Flanges
- Non-Metallic Flanges (FRP/GRP/GRE Flanges)
- Metallic Flanges
In conclusion, knowing the right type enables you to know when to use them and for what purpose. This prevents the misuse of pipe flanges when using them for engineering purposes.
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