How many kinds of flanges?

There are many types of flanges, mainly according to their nominal diameter (type A B type, ie metric system), nominal pressure, use structure, material, sealing surface form, connection type (diameter and pressure rating are not included) according to the flange Forms are divided into: plate flange (PL), slip on flange (SO), welding neck flange (WN), integral flange (IF), socket weld flange (SW), thread Flange (Th), loose flange; according to the form of sealing surface: protruding surface (RF), concave and convex surface (MFM), gutter Surface (TG), full plane (FF), ring joint surface (RJ); flange cover is not included here; according to materials: cast iron flange, cast steel, forged, Q235, stainless steel flange, plastic flange, etc.

As a kind of indispensable spare part in piping design, flanges can be used in a wide range of fields, such as industrial furnace, water supply and drainage, heating and ventilation.

Materials:

  • WCB carbon steel
  • stainless steel, 316L, 316, 304L, 304, 321, Cr-Mo steel, Cr-Mo-V steel, 316Ti

Classification:
Ring flange, welding neck flange, slip-on flange, blind flange, orifice flange, threaded flange, socket weld flange,  etc.
Standard:

  • GB standards
  • JB standards
  • HG standards
  • ASME (U.S.)
  • BS4504 (British)
  • DIN (Deutsches)
  • JIS (Japan)

11 Kinds of Flanges and Their Characteristics

Welding Plate Flange

Pro: easy obtaining, simple manufacturing, low cost, a wide range of applications
Con: It is not solid enough to be used in flammable, combustible, or high-vacuum pipe system and other highly dangerous situations.
Face type: flat face and raised face

Slip-on Flange

Pro:

  1. Easy installation, 
  2. Non-destructive inspection can be omitted.

Con:

  1. Short neck, inadequate rigidity, bearing capacity
  2. Heavy workload of welding, high consumption of welding rod
  3. Unable to bear high temperature and pressure, repeated bending and temperature fluctuation

Welding Neck Flange
Face type: RF, FM, M, T, G, FF
Pro: 

  1. Not easy to deform when connecting, good sealability
  2. It is able to be used in situations with drastic fluctuation of temperature, pipeline with high pressure, high or cryogenic temperature. 
  3. It can also be used in pipeline that transports flammable and combustible media, toxic gases, expensive media.

Con:

  1. Bulky, heavy and expensive
  2. Difficult installation and positioning

Integral Flange

Integral flange, also called long weld neck flange (LWN flange), is normally forged and widely used in pipeline with high pressure. 
Materials: Carbon steel, stainless steel, alloy steel, etc.
Precaution: For flammable, combustible and highly dangerous situations, choose MFM and TG face types, rather than RF.

Socket Weld Flange

It is a flange whose one side is welded with pipe and the other side is connected by screws.
Face type: RF, MFM, TG, RJ
Application: Boiler and pressure vessels, petroleum, chemical engineering, ship building, pharmacy, metallurgy, mechanical engineering,  food industries, etc. (pipeline: PN≤10.0MPa, DN≤40)

Threaded Flange

It is a non-welded flange whose inner bores are processed into pipe threads so as to connect with pipes that have treads.
Pro:
Compared to welded flange or WN flange, it has advantages such as convenient installation and maintenance, being suitable for situations where welded flange or WN flange cannot be used, a replacement of alloy steel flange, which has high rigidity, yet is hard to weld.
Con:

Threaded flanges are not recommended to be used (to prevent leaking) in situations where has drastic changes of temperature or temperature higher than 260℃ or lower than -45℃.

Blind Flange

It is a flange without any bore in the middle in order to block off media through a pipeline, like what welded cap and casing cap function, except that only casing cap and blind flange are able to be uninstalled at any time.
Blind Flange with Anti-Corrosion Lining
It is a kind of blind flange whose side which is close to media is welded with stainless steel and is used as a blind plate that blocks off corrosive media.

Lap Joint Flange with Welding Neck Collar

It is a movable flange assorted with fitting for water supply and drainage.
Function:
The main purpose of using lap joint flange with welding neck collar is saving materials, which is by making flange plate with low-grade materials and the tube part using the same materials with pipeline.
Advantages:

  1. Saving cost
  2. Being able to connect with pipes that are inconvenient to weld, such as plastic pipes, RPM pipes
  3. Easy installation

Disadvantages:

  1. It can only withstand low pressure
  2. Low intensity (especially when thickness is less than 3mm)

Lap Joint Flange with Welding-on Collar

It is also a movable flange plate that is directly connected with pipeline, and screws used in the device. The structure of lap joint flange with welding-on collar can be divided into two parts: pipe, which connects with pipeline on one of its end side and the other end side is designed as a cuff; along with flange plate that is set on the cuff.
Advantages:

  1. Being able to connect with pipes such as plastic pipes, RPM pipes
  2. Easy construction
  3. Saving cost

Disadvantages:

  1. Being unable to bear with high pressure
  2. Low intensity (especially when thickness is less than 3mm)

Slip-on Flange (US standard)

Slip-on Flange is a spare part that connects pipe and pipe, with bores, and screw bolts can be threaded on it so as to connect two flanges, between which a gasket is used for sealing. After screws are tightened, the gasket will deform and fill the irregular surface due to the ratio of surface sealing pressure has reached to a certain figure, thus the connection will be leakless. Connecting by flanges is a dismountable connection type that can be categorized into vessel flanges and pipe flanges according to which part they are going to connect. Normally, slip-on flanges are applicable to connecting with pipes whose nominal pressure are under 2.5MPa.
The structure of welding slip-on flange and pipe has a relatively high strength, rigidity and reliable sealability, also, it is practical enough to be able to withstand high temperature and pressure, repeated bending as well as temperature fluctuation. Slip-on flanges with 0.25-2.5MPa pressure adopt M&F (male and female) face type.

Welding Neck Flange (US standard)

Welding neck flange (US standard) has two manufacturing methods: forging and casting. The connection is with two flange plates and one gasket between them, which are tightened by screws through the bores on the flange.

 

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