10 types of flanges

What are flanges?

Flanges are a type of component that is extremely common in engineering design and involves a wide range of surfaces. It is an indispensable part of piping design and pipe fittings, and it is also an essential component in equipment and equipment parts (such as manholes, sight glass level gauges, etc.). In addition, other professional industries such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, automatic control, etc., often use flange joints.

Forged steel, WCB carbon steel, stainless steel, 316L, 316, 304L, 304, 321, chromium-molybdenum steel, chromium-molybdenum-vanadium steel, molybdenum-titanium, rubber-lined, lining fluorine material.
Flat welded flanges, neck flanges, butt weld flanges, ring joint flanges, socket flanges, and blind plates.
Implementation standards:
There are GB series (national standard), JB series (mechanical department), HG series (Ministry of Chemical Industry), ASME B16.5 (American standard), BS4504 (British standard), DIN (German standard), JIS (Japanese standard).
International Flange Standard System:
There are two main systems in the international flange standard, namely the European flange system represented by German DIN (including the former Soviet Union) and the American flange system represented by American ANSI flange.

9 types of flanges and sealing surface forms:

1. Weld Neck Flange

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A weld neck flange is a type of steel flange designed to transfer stresses to the pipe to reduce high stress concentrations at the base of the flange. Compared with other types,weld neck flanges are know for their tapered hub and gentle transition from flange thickness to pipe wall thickness. They are deformation-resistant, and are normally used for high pressure piping system, high or low temperature conditions. 

Flange Facing Types

America Series:Flat face(FF),Raised face(RF),Tongue(T),Groove(G),Female(F),Male(M),Ring type joints face(RJ/RTJ)

Europe Series:Type A(Flat Face),Type B(Raised Face),Type C(Tongue),Type D(Groove),Type E(Spigot),Type F(Recess),Type G(O-Ring Spigot),Type H(O-Ring Groove)

The connection is not easy to be deformed, the sealing effect is good, and it is widely used. It is suitable for pipes with large fluctuation of temperature or pressure or pipes with high temperature, high pressure and low temperature. It is also used for pipes conveying expensive medium, inflammable and explosive medium and toxic gas.
The flange with neck butt welding is bulky, cumbersome, expensive and difficult to locate. Therefore, it is easier to bump in transportation.

2. Slip On Flange

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Slip on flange is a type of steel flange which slides over the end of steel piping and then welded in place.Because the pipe slips into the flange before welding,it has a low hub.The inside and outside of the flange are both welded,resulting in sufficient strengh and no leak. Yaang slip on flanges can be easily fitted and welded into different pipes.It is perfect for lower pressure applications.

It is convenient for welding or easy to process or require strong strength, such as plastic pipes, glass steel pipes and so on.
Easy construction, such as connecting the flange bolt hole corresponding to facilitate the alignment or prevent future replacement of equipment flange bolt hole change.
When the price is high, save money. When the pipe material is special, the flange with the same material is expensive.
Accept low pressure.
The strength of the weld ring is low (especially below 3mm thickness).

3. Threaded Flange

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A threaded Flange is used for special circumstances with their main advantage being that they can be attached to the pipewithout welding.  Sometimes a seal weld is also used in conjunction with the threaded connection.  This special type of flange is generally used for high pressure piping system, yet smaller diameter applications.  Obviously, the larger the flange is, the harder the ability to machine a thread would be.  

Compared with flat welding flange or butt welding flange, thread flange has the characteristics of easy installation and maintenance, and can be used in some pipelines which are not allowed to be welded on site. Alloy steel flange has enough strength, but it is not easy to weld, or welding performance is not good, can also choose thread flange.
It is recommended that no threaded flange be used to avoid leakage when the temperature changes rapidly or the temperature is higher than 260 °C below -45 °C.

4. Blind Flange

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A blind flange is a popular type of pipe flanges.It has no bore in the center,and is primarily used to close the ends of piping systems.This flange premits easy access to a line once it has been sealed.It sometimes can be machined to accept a nominal sizes pipe to which a threaded or welded reduction is being made. Yaang steel blind flanges are available in various sizes and material for you to choose from.

5. Spectacle Flange

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A spectacle blind – also known as a figure-8 blind – is generally a piece of metal that is cut to fit between two pipe flange and usually sandwiched between two gaskets. A spectacle blind is often made from two metal discs that are attached to each other by a small section of steel. The shape is similar to a pair of glasses or “spectacles” – hence the name spectacle blind. One end of the blind will have an opening to allow flow through the pipe during operation and the other end is solid to block flow during maintenance. They are generally installed as a permanent device to separate process piping systems. 

6. Integral Flange (Long Weld Neck Flange)

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A Integral Flange which is also called Long weld neck flange (LWN flange), is used for high pressure situations, integral hub weld neck flanges are used and for very high pressure cases Long Welding Neck flanges are preferred. In this case, the weld are far from the ring to avoid bending stresses and weld stress being combined.  

7. Orifice Flange

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Orifice Flanges are used with orifice meters for the purpose of measuring the flow rate of either liquids or gases in the respective pipeline.  Orifice flanges generally come with either raised faces or RTJ (Ring Type Joint) facings.They are,for all intensive purposes,the same as weld neck and slip-on flanges with extra machining.They have modifications of radial tapped holes in the flange ring for meter connections and orifice plate carriers for the reason of fitting meter connections.The additional bolts act as a jack to allow the separation of the two flanges to change the orifice plate or for other inspection services.

8. Socket Weld Flange

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A Socket Weld Flange is similar to slip-on flanges, however, socket welds have an internal recess on the inside diameter to allow for a smoother flow of the process fluid.  The positive of this is that is creates a smooth bore with the proper welding and grinding.  The negative of this type of flange is that it can be more expensive than a slip-on due to more intricate machining, and they can be less readily available than slip-ons due to the fact that the bottom half of the inside diameter must be made to the same schedule as the pipe that is being used. (you must specify the schedule needed)  These socket weld flanges were initially developed for use on smaller sizes of pipe at higher pressure ratings.

9. Plate Flange

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A plate flange  is a flat, circular disk that is welded onto the end of a steel pipe and allows it to be bolted to another pipe. Typically used in fuel and water pipelines, the two flange plates will be bolted together with a gasket in between them. The flange plate will have bolt holes all around the perimeter and will be used to create junctions, tees and joints. 

10. Non-Standard Flange

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Non-standard flange is usually used for customers’ special requirement. They indicate the application service ,the data,the specification and the drawing . Then we produced the special flanges according to their requirement.


Plate flange: 1/4″-160″DN8-DN4000

Flange Pressure-Temperature Class (Service Rating)

Flange are classified as per their pressure-temperature ratings which are designated as 150#, 300#, 400#, 600#, 900#, 1500# and 2500#. Large diameter flanges that is 24” to 60” are available up to 900# class. Pressure-temperature ratings are maximum allowable working gage pressures in the bar & the temperatures in degrees Celsius.

Higher the rating, heavier the flange and can withstand higher pressure and temperature. When the temperature goes up, the pressure goes down, and vice versa. Please note that different material has different pressure ratings.

Flange Facing Types

Based on Flange facing Types, it can be further classified as:

  1. Flat Face (FF)
  2. Raised Face (RF)
  3. Ring Joint (RTJ)
  4. Tongue and groove (T&G)
  5. And Male and Female type

Flange Facing Types - 10 types of flanges

Flat Face

As name suggest, flat face flange has a flat face. Flat face flanges are used when the counter flanges are flat face. This condition occurs mainly on connection to Cast Iron equipments, valves and specialties. Full face gasket is used when flat face flange is used.

Raised Face

Raised face flange has small portion around the bore is raised from the face. The gasket seat on this raised face. The height of the raised face depends on the flange pressure temperature rating that is known as a class of the flange. For 150# & 300# height of the raised face is 1/6” and above 300# it is 1/4”. The inside bore circle type of gasket is used with raised face flange.

RTJ Face

Ring joint type face flange has a specially designed grove in which metal gasket seat. This type of flange is used in high pressure and temperature services.

Flange Face Types - 10 types of flanges

Serration on the Flange Face

The flange face has small grooves as you can see in the image. This machining is known as a serration.  Flange face can be smooth or serrated type. Which type of face to use is depends on the type of the gasket and service of the fluid.

Flange Face - 10 types of flanges

Smooth finish is used with metallic gasket whereas serrated finish is used with non-metallic gasket.  Soft material of gaskets is set in this serration and prevent liquid or gas from passing from flange joint.

Serration can be spiral or concentric rings as you can see in the slide. Concentric rings type finishing is used when fluid is of very low density. If you use spiral type finish with very low density fluid, it may find leakage path through the spiral cavity.

Flange Face design - 10 types of flanges

Serration of flange face is specified in RMS (Root Mean Square) or AARH (Arithmetic Average Rough Height), the most common value of serrated face is 120-250 AARH. Comparator gauge is used to check serration of the flange. In the image, you can see the how gauge is used to verify the value of serration.

Comparator Gauge - 10 types of flanges

Material of flanges

  • Carbon steel: ASTM A105,ASTM A105N,GB 20,C22.8.
  • Alloy steel: ASTM/ASME A182 F1-F12-F11-F22- F5-F9- F91
  • Stainless steel: ASTM/ASME A182 F304-304L-304H-304LN-304N
  • ASTM/ASME A182 F316-316L-316H-316LN-316N-316Ti
  • ASTM/ASME A182 F321-321H, F347-347H
  • Low temperature steel: ASTM/ASME A350 LF2.
  • High performance steel: ASTM/ASME A694 F42 , F52, F56, F60, F65, F70

Flange Pressure-Temperature Class (Service Rating)

Flange are classified as per their pressure-temperature ratings which are designated as 150#, 300#, 400#, 600#, 900#, 1500# and 2500#. Large diameter flanges that is 24” to 60” are available up to 900# class. Pressure-temperature ratings are maximum allowable working gage pressures in the bar & the temperatures in degrees Celsius.

Higher the rating, heavier the flange and can withstand higher pressure and temperature. When the temperature goes up, the pressure goes down, and vice versa. Please note that different material has different pressure ratings.

Flange Material

Flanges are manufactured from

  • Carbon steel
  • Low alloy steel
  • Stainless steel
  • Or Combination of Exotic materials (Stub) and other backing materials

List of materials used to manufacture flanges is covered in ASME B16.5 & B16.47.

  • ASME B16.5 -Pipe Flanges and Flanged Fittings NPS ½” to 24”
  • ASME B16.47 -Large Diameter Steel Flanges NPS 26” to 60”

Commonly used Forged material grads are

  • Carbon Steel: – ASTM A105, ASTM A350 LF1/2, ASTM A181
  • Alloy Steel: – ASTM A182F1 /F2 /F5 /F7 /F9 /F11 /F12 /F22
  • Stainless Steel: – ASTM A182F6 /F304 /F304L /F316 /F316L/ F321/F347/F348

Flange Inspection

Following to be confirmed during inspection of flange

  • Outer & Inner Diameter of body
  • Bolt Circle & Bolt hole Diameter
  • Hub Diameter & thickness of weld end
  • Length of the Hub
  • Straightness and alignment of the bolt hole

Permissible tolerances are given in B16.5 and B16.47 standard.

Flange Inspection - 10 types of flanges


Following shall be marked on flange body

  • Manufacturer logo
  • ASTM material code
  • Material Grade
  • Service rating (Pressure-temperature Class))
  • Size
  • Thickness (Schedule)
  • Heat No
  • Special marking if any QT (Quenched and tempered) or W (Repair by welding)

Flange Marking - 10 types of flanges


  • ASME ANSI B16.5,
  • AWWA C207
  • MSS SP 44
  • CSA Z245.12
  • EN1092-1,EN1759-1.
  • DIN2573 ,DIN2576,DIN2501,DIN2502.
  • BS1560,BS 4504,BS 10.
  • AFNOR NF E29-200-1
  • ISO7005-1
  • AS2129
  • JIS B2220
  • UNI 2276. UNI 2277.UNI 2278 .UNI 6089 .UNI 6090

Industrial Processes

Die forging,Machining.

Application for Plate flanges

Natural gas,chemical,petroleum,ship building,marine,paper making, metallurgy, electric, power, boiler , etc.

Source: China Pipe Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(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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