A comprehensive guide to pipe flanges

Pipe flanges, as a mechanical element, play an indispensable role in the connection of pipes, valves, equipment, etc. It achieves a detachable connection through the cooperation of bolts and gaskets to ensure the stability and sealing of the connection. Its standards, types, and size comparisons under different standards are important knowledge that beginners need to master.

Components of pipe flanges:

• Flange body: This is the core part of the flange, providing a solid foundation for mechanical connection and sealing.
• Bolt holes: These holes are designed for inserting bolts to firmly fix the flange position.

• Sealing surface: This surface is in close contact with the gasket to achieve the sealing function of the connection.

Flange standard classification:

Different countries and regions use different flange standards, which specify the design, size, tolerance and material requirements of the flange in detail. The following are several major standard classifications:

American Standard (ASME/ANSI B16.5): American standard, widely used in international engineering projects, with high pressure rating range and strong versatility.
German Standard (DIN EN 1092-1): German standard, widely used in Europe, classified according to different pressure levels.

Chinese Standard (GB/T): Chinese national standard, covering a variety of flange types, such as flat welding flange, flat welding flange with neck and butt welding flange with neck, etc.

Pipe flange type:

Pipe flanges are of various types, suitable for different working conditions according to their different structural forms and connection methods. The following are some common flange types and their characteristics:

Classification by structural form:

1. Flat welding flange: The pipe is directly inserted into the flange for welding, which is easy to install and suitable for low-pressure occasions. Its advantages are low cost and easy installation, but relatively low strength.
2. Butt welding flange: It consists of two butt-welded steel plates or forgings, with high strength and sealing, suitable for medium, high pressure and high temperature occasions. Although the manufacturing cost is high, its advantage is that the strength and sealing after welding are significant.
3. Socket welding flange: One end is welded to the steel pipe and the other end is connected with bolts. It is commonly used in pipelines with PN≤10.0MPa and DN≤40.

4. Threaded flange: connected to the pipe through threads, suitable for small diameter and low pressure occasions. No welding is required, but it is not suitable for high temperature and high pressure environments.
5. Loose sleeve flange: adopts loose sleeve connection method, which is easy to install and disassemble, especially suitable for occasions that need to be replaced frequently. Its advantage is that it is easy to install and disassemble.
6. Blind flange: used to seal the pipe end, with a hole-free design, good sealing and applicability.

Classification by material:

Carbon steel flange: made of carbon steel material, usually used for general industrial pipeline connection.
Stainless steel flange: made of stainless steel material, suitable for the connection of corrosive medium pipelines.
Alloy steel flange: made of alloy steel material, suitable for the connection of high temperature and high pressure pipelines.
Copper flange: made of copper material, usually used for the connection of water supply pipelines.
Plastic flange: made of plastic material, suitable for the connection of plastic pipes.

Classification by sealing surface form:

Raised face (RF): the most common sealing surface form, suitable for most occasions.
Concave and convex face (MFM): suitable for occasions with slightly higher pressure.
Tongue-and-groove surface (TG): Suitable for flammable, explosive, toxic media and high pressure occasions.
Full plane (FF): Suitable for low pressure and non-toxic media occasions.
Ring joint surface (RJ): Used in specific high-pressure sealing occasions.

Uses of pipe flanges:

Flange pipe fittings play a key role in many fields, and their uses are wide and indispensable. The following are some of the main application scenarios of flanges:

1. Pipeline connection: Flange is a bridge connecting pipelines to ensure the stability and sealing of the connection.
2. Equipment connection: The connection between pumps, valves and other equipment and pipelines is also inseparable from flanges, which provide these equipment with interfaces for connection to the pipeline system.
3. Maintenance and replacement: The bolt connection design of the flange makes disassembly and maintenance simple, and also facilitates the replacement of equipment.
4. Application in high-pressure occasions: In the petroleum, chemical and other industries, special flanges are widely used in high-pressure environments to ensure the safe operation of the system.

Comparison of flange sizes of different standards:

Flange standards in different countries and regions differ in size. The following is a comparison of several major standard sizes:

1. Diameter range: The diameter range covered by the national standard and the German standard is roughly the same, while the range of the American standard is in inches, which is slightly different.
2. Number of bolt holes: In each standard, the number of bolt holes varies with the pressure level, but the specific number of holes and layout will vary.
3. Pressure level: The national standard and the German standard use the PN mark, while the American standard uses the Class mark, which reflects the pressure level range under different standards.
4. Specific size comparison examples: This section will provide a more detailed size comparison to help users more clearly understand the differences in flange sizes under different standards.

How to choose a pipe flange?

When choosing a flange, you need to consider multiple factors. Here are a few key selection points:

Choose according to the pressure level: In low-pressure environments, flat welding flanges and threaded flanges are suitable choices; in high-pressure environments, neck butt welding flanges or ring connection flanges should be used to ensure the stability of the connection.

Consider the sealing requirements: If high sealing is required, flanges with concave and convex surfaces or ring connection sealing are preferred; for ordinary occasions, flanges with flat sealing are sufficient.

Determine according to the applicable standards: Domestic engineering projects usually adopt the national standard (GB); while international projects may involve the American standard (ANSI) or the German standard (DIN), which needs to be selected according to the specific situation.

Advantages and precautions of pipe flanges:

The advantages of using flange pipe fittings include reliable connection, good sealing, and convenient installation and removal. At the same time, flanges are also suitable for a variety of occasions and have a variety of material options. However, during use, some matters should also be noted, such as ensuring that the flange is correctly selected according to the pressure level, tightening the bolts evenly, and selecting the appropriate sealing gasket material to ensure that the flange can perform at its best.

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