Applications of Flanges

Flanges are integral parts of many engineering and plumbing projects. Used in many, different fields, such as the transport (pipelines, ships) of petroleum, gas, water, etc., their manufacturing facilities and those of power generation, chemicals, and chemical fertilizers, flanges are of various kinds in type and shape, and their material too is diversified (low carbon steel, low alloy steel, stainless steel, high alloy steel, non-ferrous steel, or such) in accordance with the type of fluid and service environment.

In many applications, engineers need to find a way to close off a chamber or cylinder in a very secure fashion, usually because the substance inside must differ from the substance outside in composition or pressure. They do this by fastening two pieces of metal or other material together with a circle of bolts on a lip. This “lip” is a flange.

You can connect two sections of metal piping by soldering or welding them together, but pipes connected in this way are very susceptible to bursting at high pressures. A way of connecting two sections of pipe more securely is by having flanged ends that you can connect with bolts. This way, even if gases or liquids build up to high pressures inside the pipe, it will often hold with no problem.


In order to connect two sections of a large, enclosed area, it is often best to used flanges and bolts. An example of this is the connection between the engine and the transmission in an automobile. In this case, both the engine and the transmission contain a number of moving parts that can easily get damaged if they get dust or other small objects inside of them. By connecting the outer casings of the engine and transmission in this way, engineers protect the inner workings of both.


Flanges have a specific purpose in cameras and other electronic devices. Though flanges in such items do not usually have to sustain high pressures, they do have to hold tight so they can keep out harmful particles. These flanges are usually found connecting two different materials, such as the glass of a lens and the rest of the body of the camera.

Applications of ANSI Long Weld Neck Flanges

Applications involving high pressure and the need for a hub that is long and tapered are what weld neck flanges are most often used for. Specifying the schedule of pipe that it will be utilized for is of utmost importance when ordering. This type of flange is excellent for use in environments involving extreme temperature fluctuations and excessive handling and bending.

Uses for Long Weld Neck Flanges

The uses for long weld neck flanges are predominantly on vessels where an extended neck is required. The uses for long weld neck flanges (LWN) are predominantly on vessels where an extended neck is required. This is deemed to be a specialty flange due to the protruding neck or hub, which acts as a boring extension.

The tapered neck aids in reducing the thickness of the steel and it then seems to be a pipe extension. Steel LWN flanges are chiefly utilized in the chemical and petroleum industries, as well as commercial and residential buildings that experience high levels of stress and temperatures that fluctuate.

Application of Spectacle blinds

Spectacle Blinds are generally applied to permanently separating pipesystems, or just to connect with each other. A Spectacle Blind is a steel plate cut into two discs of a certain thickness.


spectacle open - Applications of Flanges


spectacle closed - Applications of Flanges

What is the use of a blind flange?

Blind flange is put at the end of pipe or at the junction that would possibly be a future expansion into that direction.


blind flange usage close the end of pipe - Applications of Flanges


blind flange usage block off a pipeline - Applications of Flanges

A blind flange is a round plate which has all of the relevant blowholes except center hole, and because of this feature the blind flange is usually used to close off the ends of a piping systems and pressure vessel openings. It also permits easy access to the interior of a line or vessel once it has been sealed and must be reopened.
Often a blind flange is inserted into a pipeline when a repair is required further up the line. This allows the flanges down stream to be disconnected without fear of losing liquid. Many times this type of blockade is used when adding another line onto an existing pipeline or when a new valve is being added. This blockade is also used to shut down a line when it is no longer needed.

Materials for Flanges Based on Applications

Steel pipe flanges have a flat rib, collar or rim that is utilized for guiding or strengthening when attaching two pipes to each other. Materials, sizes and opening dimensions are varying based upon applications that the flanges are designed for and include threaded, socket-wired and slip-on styles.

Flanged connection

A flange is a external rib at the end of pipes, valves and other flow devices to assemble them.
Dimensions of the flanges are up to specific Standards : DIN, ANSI, AS, BS, JIS

A flanged connection requires two flanges (the “main” and the “companion”), a set of bolts and nuts (whose number depends on the flange diameter and class) and two sealing gaskets. Flanged connections have to be executed and supervised by trained personnel, as the quality of the joint has a critical impact on the performance of the piping system / pipeline (the standard TSE – TS EN 1591 Part 1-4, “Flanges and their joints”, defines a number of requirements for the execution of proper flanged connections). Whereas all elements of the joint are critical, experience shows most leaks are originated by the improper installation of the sealing elements, i.e. the gaskets.

The typical pipe to flange connections are welded or threaded. Welded flanges are used for pipelines and piping systems with high pressures and temperatures, and with diameters above 2 inches. Threaded connections are instead used for installations of smaller diameter and not subject to severe mechanical forces such as expansion, vibration, contraction, oscillation (forces that would crack the threaded joint). In all these critical cases, butt weld connections are recommended.

Types of face flanges

There are different flanges profiles.

Raised Face Flanges (RF):
RF flanges seal with a flat gasket designed for installation between the raised faces of two mating flanges (both with raised faces). The raised faces have a prescribed texture to increase their gripping and retaining force on this flat gasket. Some users of raised face flanges specify the use of spiral wound gaskets.

ring type joint flange rtj - Applications of Flanges

Ring Type Joint Flanges (RTJ) or Ring Joint Facing Flanges (R-JF):
RTJ flanges have grooves cut into their faces which accept steel Ring Gaskets. RTJ flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or “Coining”) the gasket to make Intimate Contact inside the grooves, creating a metal to metal seal.
An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means. For RTJ flanges that seal with BX ring gaskets, the raised faces of the connected and tightened flanges may contact each other. In this case the compressed gasket will not bear additional load beyond the bolt tension, vibration and movement cannot further crush the gasket and lessen the connecting tension.

Connection Types of Flanges

Connection types of flanges can generally be divided into five kinds: flat welding, butt welding, socket welding, loose and threaded.

Flange Facing Types - Applications of Flanges

Flange easy to use, able to withstand greater pressure. Below is the detailed description of first four kinds:
1. Flat welding: only for welding outer layer, welding inner layer is not required; normally, it often used in medium, low pressure pipes. Nominal pressure of pipe is lower than 2.5Mpa. Sealing surface of flat welding flanges has three kinds: smooth type, concave-convex type and tongue and groove type. Among them, smooth type is the most widely used with cost effective.
2. Butt welding: both outer and inner of flange need to be welded. Normally, it is widely used in medium and high pressure pipes. Nominal pressure of pipe is between: 0.25-2.5Mpa. Seal surface of connection type of butt welding flange is concave-convex type with complex installation. Therefore, cost of labor, installation method and auxiliary is a little high.

3. Socket welding:
 normally, it is used in the nominal pressure lower than 10.0 Mpa. Nominal diameter is lower or equal to 40mm of pipe.
4. Loose: normally used in the pipes with not high and its medium is a little corrosive. Therefore, this kinds of flange is corrosion resistant. The material is mainly stainless steel.

Forged flange applications

Forged flanges are used as a connection component for pipes, valves, pumps and other equipment to form a pipework system. They provide easy access for cleaning, inspection, modification or repairs. Flanges are usually welded onto pipes or screwed onto a threaded pipe end and then joined with bolts to make the connection.

Flanges are classified in form as shown Figure 2 according to the method of linking with pipes, and their form of face is classified as shown in Figure 3 pursuant to the type of gaskets used. Like this, their forms are diverse under designated different conditions, and so it is necessary to indicate clearly the items shown in Figure 1 at the time of order placement. ( Both Figures 2 and 3 are quoted from JPI-7S-15 standards.) 

instruction01e - Applications of Flanges

Figure 1: Items requiring indication when an order is placed.

instruction02e - Applications of Flanges

Figure 2: Form of flanges

instruction03e - Applications of Flanges

Figure 3: Form of gaskets

(1) Applicable Material Standards & Material Codes
The material used most often for flanges includes low carbon steel, low alloy steel, and stainless steel (individual detailed material designation omitted), and applicable standards are roughly classified into JIS (Japan Industrial Standards) for domestic projects and ASME(American Society of Mechanical Engineers) and ASTM(American Society for Testing Materials) for foreign projects. 
In addition laws and regulations, such as the High Pressure Gas Security Law, the Nuclear Power Notification, and the Electric Utility Industry Law, are applied depending on projects, and hence the requirements, such as manufacturing procedures, inspection items, and the necessity of qualification approval, differ depending on these applicable standards, laws and regulations. 
(2) Applicable Form Standards
The form standards of the flanges manufactured by our company are classified into the following groups.
A. JIS-system Typified by JIS2220, in which nominal pressure is expressed in k.
B. ASME-system Typified by ASME16.5, in which nominal pressure is expressed in Lbs.
(old ANSI standards)
B16.5(small & medium bore diameter) -> To JPI-7S-15
B16.47(large bore diameter)Series A <- MSS-SP-45 included
-> To JPI-7S-43
Series B <- API-605 included.
-> To JPI-7S-43
C.Others-1: Flanges to which are applied the high pressure flange standards for oil drilling rigs in which API-6A and 6B get typified and nominal pressure is expressed in PSI.
D.Others-2: Flanges with the form designed, developed by a user or manufacturer.
E. Not manufactured by our company and typified by DIN(German Industrial Standard) in which nominal pressure is expressed in PN(nominal pressure). Some flanges to which EN (European Union Standards) standards are applied.

As stated above, there are various form standards, and since design philosophy, dimensions, and forms differ largely depending on standards, it is necessary to give an precise indication. 

(3)Pressure class
Pressure class (nominal pressure) differs depending on standards pursuant to the difference in the design basis of each standard set forth in the preceding section. The pressure class of each standard is as follows:
  • JIS-system
  • ASME- and JPI-system
  • API-6A :2000 PIS、3000 PIS、5000 PIS、10000 PIS、15000 PIS、20000 PIS
  • EN standard-system : PN10、PN16、PN20、PN50、PN110、PN150、PN260、PN420
(4) Form Classification
As shown in Figure 2, the following fundamental forms are standardized according to the means of linking up with pipes. 
  • Welding Neck: WN
  • Slip-on Welding: SO
  • Integral or Long Welding Neck: LWN
  • Socket Welding: SW
  • Threaded or Screwed
  • Lapped Joint: LAP
  • Blind: BL

Apart from the above forms, what is called a reducing flange is also standardized as their application version.

(5) Type of Face
It is a face called a gasket contact surface that is considered the most important portion of a flange. As shown in Figure 3 its forms are classified depending on the type of gaskets used. And not only forms but also the finish roughness accuracy of machined surfaces are specified meticulously. It is the portion which plays an important role in the sealability to prevent fluid from leaking. Heed must be paid to the fact that the thickness and total height of flanges differ depending upon FF(Flat Face), RF(Raised Face), and RTJ(Ring Joint) even if the pipe size, nominal pressure, or type (WN type for instance) is Identical. 
(6) Applicable Pipe Diameter and Pipe Wall thickness (SCH.NO.)
For the pipe nominal diameter, Indication A is used in JIS and Indication B in ASME-system standards respectively, and 10A to 1500A (1/8B to 60B) is specified in each of these standards. And SCH. NO. (schedule No.) means the number showing the wall thickness classification of pipes. Here wall thickness increases with increasing SCH.NO. It is noted, however, that any size does not have the same wall thickness under the same SCH. NO., but all the wall thickness differs size by size depending on SCH. NO. 
There is a range (5B, 6B, 8B, 10B, 12B) differing in outer diameter between JIS and ASME(ANSI) pipes even if the nominal diameter is identical, and the difference in outer diameter causes the inner diameter too to change each SCH. NO. 
There occurs difference in the outer and inner diameter of groove portions for flanges, like SO type, welded by inserting a pipe into these, flanges, like WN type, butt-welded with a pipe, and flanges, like SW type, whose inner diameter coincides with that of a pipe.
In case of connecting a JIS pipe to an ASME flange, or in the reverse case, it is likely that unless the manufacturing side is informed in advance of such connection, there occurs trouble during welding at the field. 

Source: China Flanges Manufacturer – Yaang Pipe Industry (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Please notice that you might be interested in the other technical articles we’ve published:
  • What are orifice flanges
  • What is a Blind Flange

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