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Type Of Flanges In Piping
The type of flange to be used for a piping application depends, mainly, on the required strength for the flanged joint. Flanges are used, alternatively to welded connections, to facilitate maintenance operations (a flanged joint can be dismantled quickly and conveniently). Which are the most common types of flanges used in piping? The key types of flanges are the welding neck, long welding neck, slip-on, socket weld, lap joint, threaded and blind flanges.
Weld Neck Flange (WNFF, WNRF, WNRJ)
Weld neck flange is also known as a high-neck flange or tapered hub flange. The weld neck flange has a neck that can properly transfer the pipe tension. It also helps to reduce the pressure gathered at the bottom of the flange. It is compatible with pipelines that operate at low or high temperatures and withstand high pressure.
Socket Weld Flanges(SWRF)
The socket weld flanges are connected on the outside just by a fillet weld. It is often not advisable for critical services. These are useful for the small-bore lines in your system. The static strength is equivalent to slip-on flanges, but the fatigue strength is 50 percent higher than double-welded slip-on flanges. Often used as an alternative to weld necks when space is a constraint.
Slip-on Flange (SORF)
The slip-on flange is a ring (with or without a hub) placed over the pipe's end. The flange face extends from the end of the pipe by a sufficient distance to apply a welded bead to the inner diameter. As the name suggests, these flanges slip over a pipe and are known as slip-on flanges.
Lap Joint Flanges
Lap joint flanges are useful with stub ends when the pipe is made of expensive material. E.g., a carbon steel flange can be added to the stainless steel pipe system as the flanges do not come into contact with the substance in the pipe.
Blind Flanges
The production of blind flanges happens without a bore and is utilized to blank off the ends of pressure vessel openings, valves, and pipes. If you look from the point of view of bolt loading and internal pressure, the most overstressed flange types are blind flanges which are quite bigger.
Threaded Flanges
Threaded flanges look identical to slip-on flanges, but the key difference is that the threaded flange is bored out to match the inside diameter of the particular pipe. The threaded flange is a type of flange that has taper pipe threads in its bore conforming to ASME B1.20.1 and is helpful in piping systems.
Materials Useful To Manufacture Flanges
Pipe flanges can be manufactured from many different materials that depend on the piping material and requirements of the application. Selection depends on the factors such as economy, flow pressure, operating temperature, and environmental corrosion. Some of the most common materials include the following:
Carbon steel
It is steel alloyed usually with carbon. The high strength and hardness increase with carbon content, lower melting point, and ductility. This is the most common material grade.
Alloy steel
It is steel alloyed with one or more elements that change or enhance the properties of steel. Common alloys include chromium, molybdenum, nickel, vanadium, and manganese.
Stainless steel
It is steel alloyed with chromium in amounts above 10%. Chromium enables stainless steel to have a much higher corrosion resistance than carbon steel which rusts readily from air and moisture exposure.
Aluminum
It is a low-density, ductile, and malleable metal with medium strength. It has better corrosion resistance compared to any other typical alloy and carbon steel. It is most useful during flange construction that requires low weight and strength.
Cast irons
Iron when it is alloyed with silicon, carbon, and several other alloys makes cast iron. Silicon forces carbon out of the iron and forms a black graphite layer on the exterior of the metal. Cast irons have good machinability, castability, and fluidity.
