Types of pipe flanges

Basic introduction of flange:

Pipe flanges and their flange gaskets and fasteners are collectively referred to as flange joints.

1. Application
Flange joints are a very common and widely used component in engineering design. Flanges are widely used in pipeline engineering, equipment connection, chemical process and other fields. It is an indispensable part of piping design, pipe fittings and valves, and it is also an essential component in equipment and equipment parts (such as manholes, sight glass liquid level gauges, etc.). In addition, other industries such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, automatic control, etc., also often use flange joints.

2. Material
Forged steel, WCB carbon steel, stainless steel, 316L, 316, 304L, 304, 321, chrome-molybdenum steel, chrome-molybdenum-vanadium steel, molybdenum-titanium, rubber lining, fluorine lining material.

3. Classification
Slip-on flange, neck flange, butt welding flange, ring connection flange, socket flange, and blind plate, etc.

4. Implementation standards:
ASME B16.5 (American standard), BS4504 (British standard), DIN (German standard), JIS (Japanese standard).
GB series (Chinese standard), JB series (Ministry of Machinery), HG series (Ministry of Chemical Industry).

5. International pipe flange standard system:
There are two main systems of pipe flange standards internationally.
European pipe flange system represented by German DIN (including the former Soviet Union)
American pipe flange system represented by American ANSI pipe flange.

Introduction to pipe flange types:

12 types of flanges and their characteristics:

1. Plate flat welding flange

Plate flat-weld flange is a flange in which steel pipes, pipe fittings, etc. are inserted into the flange and connected to equipment or pipelines through corner welds. It is referred to as flat-weld flange. Plate flat-weld flange is mainly used for general media.

Advantages:
Easy to obtain materials, simple to manufacture, low cost, and widely used.

Disadvantages:
Poor rigidity, so it should not be used in chemical process piping systems with supply and demand, flammable, explosive and high vacuum requirements, and high and extremely hazardous occasions.

Plate slip-on flange is the most common flange, with pressures of PN2.5, PN6, PN10, PN16, PN25, and PN40. The sealing surface types are raised face (RF) and full plane (FF).
Welding form: Plate slip-on flange is to insert the pipe into the flange for welding.

2. Neck-welded flange

Neck-welded flange is the full name of neck-welded steel pipe flange, which is a flange that connects steel pipes, pipe fittings, etc. into the flange through fillet welds to equipment or pipelines. It is also one of the commonly used flanges on equipment or pipelines.

Advantages:
Neck-welded flange is also a flat-weld flange, because it has a short neck, which improves the strength of the flange and improves the bearing capacity of the flange. Therefore, it can be used on pipelines with higher pressures. It is more convenient to install on site.

Disadvantages:
The neck height of the neck-welded flange is lower, which improves the rigidity and bearing capacity of the flange. Compared with the butt-welded flange, the welding workload is large, the consumption of welding rods is high, and it cannot withstand high temperature, high pressure, repeated bending and temperature fluctuations. Compared with plate-type flat-weld flanges, it is more expensive and more prone to bumping during transportation due to its shape.

Applicable pressure range: PN series: PN2.5~PN40; Class series: Class150~Class1500.

The sealing surface forms of the neck flat-weld flange are:
Raised face (RF), concave face (FM), convex face (M), tenon face (T), groove face (G), full plane (FF).

3. Neck butt-weld flange

Neck butt-weld flange refers to a flange with a cone neck and butt-welded to the cylinder or pipe. It is an integral flange.

Advantages:
Due to the transition structure of the cone neck and the butt welding connection, the strength and rigidity of the flange are enhanced, and the sealing is better than that of the flat-weld flange.

The connection is not easy to deform, the sealing effect is good, and it is widely used. It is suitable for pipelines with large fluctuations in temperature or pressure or high temperature, high pressure and low temperature pipelines. It is also used for pipelines that transport expensive media, flammable and explosive media, and toxic gases.

Disadvantages:
It needs to be made of forgings, which consumes a lot of materials and has high manufacturing costs. It is also large in size, heavy in weight, expensive, difficult to install and position, and more likely to bump during transportation. It is suitable for occasions with high pressure and temperature or high sealing requirements.

The sealing surface forms of neck-welded flanges are:
Raised face (RF), concave face (FM), convex face (M), tenon face (T), groove face (G), full plane (FF).

4. Integral flange

Integral flange is a flange connection method. It is also a type of neck-welded steel pipe flange. The materials include carbon steel, stainless steel, alloy steel, etc.

In various domestic standards, IF is used to represent integral flanges. It is mostly used in pipelines with higher pressure, and the production process is generally casting.

In the flange type, an "IF" is used to indicate the type of integral flange. It is generally a raised face (RF). If it is used in flammable, explosive, high and extremely hazardous conditions, you can choose the sealing surface forms of convex and concave faces (MFM) and tenon and groove faces (TG) in addition to the RF face.

5. Socket welding flange

Socket welding flange refers to the flange in which the end of the pipe is inserted into the flange ring step and welded at the pipe end and the outside. There are two types: with neck and without neck. The neck pipe flange has good rigidity, small welding deformation, good sealing, and can be used in occasions with a pressure of 1.0~10.0MPa. Type B flange for container is also a socket welding flange, which is used in occasions with high sealing requirements. When designing, the socket welding flange can be checked according to the integral flange.

Sealing surface form:
Raised face (RF), concave and convex face (MFM), tongue and groove face (TG), ring joint face (RJ).

Application range:
Boiler pressure vessel, petroleum, chemical industry, shipbuilding, pharmaceutical, metallurgy, machinery, food and other industries.

Commonly used in pipelines with PN≤10.0MPa and DN≤40.

6. Threaded flange

The threaded flange is a non-welded flange in which the inner hole of the flange is processed into a pipe thread and connected with a threaded pipe. When designing, it can be treated as a loose flange.

Advantages: 

Compared with flat welding flanges or butt welding flanges, threaded flanges are easy to install and maintain. They can be used on pipelines where welding is not allowed on site. When the flange is deformed, the additional torque on the cylinder or pipeline is very small. Alloy steel flanges have sufficient strength, but are not easy to weld, or have poor welding performance. Threaded flanges can also be selected.

Disadvantages:
It is recommended not to use threaded flanges under conditions where the pipeline temperature changes sharply or the temperature is higher than 260℃ and lower than -45℃ to avoid leakage. The flange is thick and the cost is high. It is suitable for the connection of high-pressure pipelines.

7. Butt welding ring loose flange

Butt welding ring loose flange is a movable flange, which is generally equipped with water supply and drainage accessories. When the manufacturer leaves the factory, there is a flange at each end of the expansion joint, which is directly connected to the pipeline and equipment in the project with bolts.

Function:
The purpose of using butt welding ring loose flange is generally to save materials. Its structure is divided into two parts. One end of the pipe part is connected to the pipeline, and the other end is made into a butt welding ring. The flange plate uses low-grade materials, while the pipe part uses the same material as the pipeline to achieve the purpose of saving materials.

Advantages:
Cost saving. When the pipe material is special and expensive, the cost of welding flanges of the same material is high. It is not easy to weld or process or requires high strength, such as plastic pipes, fiberglass pipes, etc. It is convenient for construction, such as the flange bolt holes are not easy to align when connecting or prevent the flange bolt holes from changing when the equipment is replaced in the future.

Disadvantages:
Low pressure resistance and low strength at the welding ring (especially when the thickness is less than 3mm).

8. Flat welding ring loose flange

The flat welding ring loose flange is a movable flange that is directly connected to the pipeline and equipment in the project with bolts.

The purpose of using a flat welding ring loose flange is generally to save materials. Its structure is divided into two parts. One end of the pipe is connected to the pipe, and the other end is made into a flange, and the flange part is sleeved on the flange.

Advantages:
It is convenient for welding or processing or requires high strength, such as plastic pipes, fiberglass pipes, etc.
It is convenient for construction, such as the flange bolt holes are convenient for alignment when connecting or prevent the flange bolt holes from changing when the equipment is replaced in the future.
When the price is high and expensive, save money. When the pipe material is special, the cost of welding flanges of the same material is high.

Disadvantages:
Low pressure acceptance.
Low strength at the welding ring (especially when the thickness is less than 3mm).

9. Flange cover

Also known as blind flange, blind plate, is a flange without a hole in the middle, used to seal the pipe plug. The function is the same as that of welding head and threaded pipe cap, except that blind flange and threaded pipe cap can be removed at any time, while welding head cannot.

Flange cover sealing surface:
Flat surface (FF), raised surface (RF), concave and convex surface (MFM), tongue and groove surface (TG), ring connection surface (RJ)

10. Lined flange cover

The lined flange cover is a blind flange with stainless steel welded on the side close to the medium as a whole. The lined flange cover is used as a blind plate on the pipeline with corrosive medium. The difference from the ordinary flange cover is that an anti-corrosion lining is added to the contact surface with the medium.

11. American standard flat-weld flange with neck

The flat-weld flange with neck is connected to the pipe end, and is mainly a part that connects pipes to each other. There are holes on the flat-weld flange with neck, which can be bolted to make the two flanges tightly connected, and the flanges are sealed with gaskets.

The gasket is placed between the sealing surfaces of the two flanges. After tightening the nut, the gasket surface deforms after the specific pressure reaches a certain value, and fills the uneven parts of the sealing surface to make the connection tight and leak-proof. Flange connection is a detachable connection, which can be divided into container flange and pipe flange according to the connected parts. The flat-weld flange with neck is suitable for the connection of steel pipes with a nominal pressure not exceeding 2.5MPa.

The flat-weld flange with neck is used for the butt welding of flanges and pipes. It has a reasonable structure, high strength and rigidity, can withstand high temperature and high pressure, repeated bending and temperature fluctuations, and has reliable sealing. The flat-weld flange with neck with a nominal pressure of 0.25~2.5MPa adopts a concave and convex sealing surface.

12. American standard butt welding flange with neck

American standard flange is a part that connects pipes to each other and is connected to the pipe end. American standard butt welding flange is made by forging and casting.

American standard butt welding flange can be divided into American standard butt welding flange with neck and American standard butt welding flange without neck according to the neck.

American standard butt welding flange consists of two flange plates plus flange gaskets, which are fastened together with bolts to complete the connection. There are holes on the American standard flange, and the bolts make the two flanges tightly connected, and the flanges are sealed with gaskets.

Read more: Standard sizes of pipe flanges or How are pipe flanges manufactured?