What are the Main Types of Flanges?

Tuesday May 8th, 2018 | Francesco Grillo | Expertise

We usually consider two main families of flanges, the standard flanges and the special ones.

What is a steel flange?

“A flange is a forged or cast ring of steel designed to connect mechanically sections of pipe or join pipe to a pressure vessel, pump, valve or any other piece of equipment.”

Usually flanges are welded or threaded and two flanges are joined to each other by bolting together them with gaskets to provide a seal. It provides an easy access to the piping system in case of cleaning, modification and inspections.

You can read about the basics of steel flange in our article What is a steel flange?

Standard Flanges

The basic types of flanges are:
  • Slip-on
  • Blind
  • Lap-Joint
  • Socket Weld
  • Threaded
  • Weld-Neck 
  • Orifice

Slip-On Flange

The flange is slipped over the pipe and is settled by welding at both top and base side of the flange. They are used to provide sufficient strength to the connection and prevent leakage. This flange is favored over weld neck flanges as less accuracy is required when cutting pipe to length, the cost to produce is lower but there is nearly the same outcome.

Blind Flanges

This is a flange without a bore. Also called a blanking flange, it is used to fix or seal an end of a piping framework or shut off a piping system or vessel opening. Inspection of vessels or piping system is easier and it is simpler to access it. A blind flange can be supplied with or without hub depending on the requirements.

Lap-Joint Flanges

This is again similar to a slip-on flange, but it has a radius at the intersection of the bore and the flange face to accommodate a lap stub end. The face on the stub end forms the gasket face on the flange. This type of flange is used in applications where section of piping systems need to be dismantle quickly and easily for inspection or replacement.

Socket Weld Flanges

This is similar to a slip-on flange in outline, but the bore is counter-bored to accept pipe. The diameter of the remaining bore is the same as the inside diameter of the pipe. The flange is attached to the pipe by a fillet weld around the hub of the flange. An optional interval weld may be applied in high stress applications. It’s biggest use is in high pressure systems such as hydraulic and steam lines.

Threaded Flanges

This is similar to a slip-on flange in outline, but the bore is threaded, thus enabling assembly without welding. This obviously limits its application to relatively low pressure piping systems. The flange may be welded around the joint after assembly, but this is not considered a satisfactory method of increasing its applications.

Weld-Neck Flanges

As ist name, this is a flange attached by welding neck of flange to a pipe. It is expensive because of its long neck, but more suitable for high stress applications because the neck provides important reinforcement to the flange. The bore of the flange matches the bore of the pipe, reducing turbulence and erosion.


Special Flanges

The special types of flanges are:
  • Groove Flanges / Tongue Flanges
  • Long Neck
  • Orifice
  • Spectacle

Groove Flanges / Tongue Flanges

A groove flange is constantly paired with a tongue flange.
The tongue flange has the face with a raised ring (i.e. the tongue). One flange has a machined raised ring (also called the tongue) and the other one has machined groove depression (also called the groove). Those two flanges should match perfectly with each other.

Tongue-and-groove facings are standardized in both large and small types. They are mainly used for pump covers and valve bonnets.

Tongue-and-groove joints have the advantage of being self-aligning and act as a reservoir for the adhesive. Major machining operation are not necessary especially thanks to the scarf joint keeping the oxis of loading in line.

Long Neck Flanges

Owing to our rich industrial experience, we are offering a comprehensive range of Long Weld Neck Flanges. The professionals of our organization source these neck flanges from trusted vendors. These flanges are unique due to their simple connectivity with other pipes. Moreover, our products are extensively used in refining industries for linking purposes. Our esteemed patrons can avail these qualitative range of flanges from us at industry-leading prices.

Orifice Flanges

The function of an orifice flange is to provide access to a line for metering of gases or liquids. An orifice plate is clamped between a pair of flanges when installed in a line and the whole assembly is refer to as an orifice flange union. Jack-screws within the assembly facilitate removal of the orifice plate. The orifice plate, the metering device, consists of a thin plate with a concentric, square edge, circular hole in the centre. Two pressure tap-holes are drilled in each flange to measure pressure difference through the orifice.

Spectacle Flanges

This is a pressure retaining plate with one solid end and one open end connected with a web or tie-bar. In normal operation, the open end forms the seal between two flanges and permits normal flow of fluid through pipe work. If the solid end is swung into position it effectively blanks of the pipe and halts the flow.


Flange faces

The ASME B16.5 and B16.47 define different types of flange facings as follows:

  • Raised Face
  • Flat Face

Raised Face Flanges

The Raised Face (RF) type is the most applied flange face, and is easy to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face.

Flat Face Flanges

The Flat Face (FF) flange has a gasket surface in the same plane as the bolting circle face. Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting.
Flat face flanges are never to be bolted to a raised face flange. ASME B31.1 says that when connecting flat face cast iron flanges to carbon steel flanges, the raised face on the carbon steel flange must be removed, and that a full face gasket is required. This is to keep the thin, bittle cast iron flange from being sprung into the gap caused by the raised face of the carbon steel flange.

General flange faces such as the Ring-Type Joint (RTJ), Male-and-Female (M&F) and Tongue-and-Groove (T&G) cannot be bolted together, because the contact surfaces do not match and there is no gasket that has one type on one side and another type on the other side.


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Please notice that you might be interested in the other product-related articles we’ve published:

  • What is Steel Forging?

  • The History of Steel Forging

  • Open Die Forging and Closed Die Forging – What’s the difference?


You can find other information here.

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