What is a pipe flange?

What is a pipe flange?

Flange, also known as pipe flange fittings. Flange is a part that connects shafts to each other and is used to connect pipe ends; there are also flanges used on equipment inlets and outlets, which are used to connect two devices, such as reducer flanges. There are holes on the flange, bolts make the two flanges tightly connected, and gaskets are used to seal between flanges. Flange is a disc-shaped part, which is most common in pipeline engineering, and flanges are used in pairs.

Flange connection:

Flange connection or flange joint refers to a detachable connection in which flanges, gaskets and bolts are connected to each other as a group of combined sealing structures. It consists of a pair of flanges, a gasket and several bolts and nuts. The gasket is placed between the sealing surfaces of the two flanges. After tightening the nuts, the specific pressure on the surface of the gasket reaches a certain value and deforms, and fills the uneven parts on the sealing surface, making the connection tight and leak-proof.

Flange connections are easy to use and can withstand greater pressure. In industrial pipelines, flange connections are widely used. Inside the home, pipes are small in diameter and low pressure, with no visible flange connections. If you are in a boiler room or production site, there are flange-connected pipes and equipment everywhere.

Classification and Type of flange:
1. Flange connection is a detachable connection. According to the connected parts, it can be divided into container flanges and pipe flanges.

2. Classification by connection method: Flanges can be divided into threaded flange, welding flange and clamp flange. Threaded flange is connected to the pipeline by thread, which is suitable for low-pressure pipeline; welding flange is connected to the pipeline by welding, which is suitable for medium and high pressure pipeline; clamp flange is connected to the pipeline by clamp, which is suitable for occasions that need frequent disassembly.

3. Classification by structure: Flanges have various structural forms, including flat welding flange, butt welding flange, socket welding flange, loose sleeve flange, etc. Flat welding flange has a simple structure and poor rigidity, which is suitable for low-pressure pipelines with pressure p≤4MPa; butt welding flange is also called high neck flange, which has higher strength and is suitable for medium and high pressure pipelines; socket welding flange is welded at one end and bolted at the other end, which is suitable for small diameter pipelines; loose sleeve flange allows flange and pipe parts to be made of different materials, which is convenient for installation and maintenance.

4‌. Classification by material: Flange materials include carbon steel, stainless steel, alloy steel, copper, plastic, etc. Carbon steel flanges are suitable for general industrial pipelines; stainless steel flanges are suitable for corrosive media; alloy steel flanges are suitable for high temperature and high pressure pipelines; copper flanges are used for water supply pipelines; plastic flanges are used for plastic pipes.

5. There are three types of flange sealing surfaces: flat sealing surfaces, which are suitable for occasions with low pressure and non-toxic media; concave and convex sealing surfaces, which are suitable for occasions with slightly higher pressure; tongue and groove sealing surfaces, which are suitable for flammable, explosive, toxic media and higher pressure occasions.

Flange gasket:
A gasket is a circular ring made of a material that can produce plastic deformation and has a certain strength. Most flange gaskets are cut from non-metallic plates or made by professional factories according to specified sizes. The materials are asbestos rubber sheets, asbestos sheets, polyethylene sheets, etc. There are also metal-clad gaskets made by wrapping non-metallic materials such as asbestos with thin metal plates (tinplate, stainless steel); there is also a wound gasket made by winding thin steel strips and asbestos strips together.

Ordinary rubber gaskets are suitable for occasions with temperatures below 120°C; asbestos rubber gaskets are suitable for occasions with water vapor temperatures below 450°C, oil temperatures below 350°C, and pressures below 5MPa. For general corrosive media, acid-resistant asbestos sheets are most commonly used. In high-pressure equipment and pipelines, lens-shaped or other shaped metal gaskets made of copper, aluminum, No. 10 steel, and stainless steel are used. The contact width between the high-pressure gasket and the sealing surface is very narrow (line contact), and the processing finish of the sealing surface and the gasket is relatively high.

International flange standard system:

There are two main systems of pipe flange standards internationally, namely the European pipe flange system represented by German DIN (including the former Soviet Union) and the American pipe flange system represented by American ANSI pipe flange. In addition, there is also the Japanese JIS pipe flange, but it is generally only used for public works in petrochemical plants and has little influence internationally. The following is a brief introduction to pipe flanges from various countries:

1) European flange system: German DIN (including the former Soviet Union)

a. Nominal pressure: 0.1, 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.4, 10.0, 16.0, 25.0, 32.0, 40.0Mpa
b. Nominal diameter: 15~2000mm
c. Flange structure type: flat welding plate type, flat welding ring loose sleeve type, rolled edge loose sleeve type, butt welding rolled edge loose sleeve type, butt welding ring loose sleeve type, butt welding type, neck thread connection type, integral type and flange cover
d. Flange sealing surfaces include: flat surface, concave surface, concave and convex surface, tongue and groove surface, rubber ring connection surface, lens surface and diaphragm welding surface
e. The OCT pipe flange standard issued by the Soviet Union in 1980 is similar to the German DIN standard.

2) American flange system: ANSI B16.5 "Steel pipe flanges and flange fittings"   ANSI B16.47A/B "Large diameter steel flanges"
a. Nominal pressure: 150psi (2.0Mpa), 300psi (5.0Mpa), 400psi (6.8Mpa), 600psi (10.0Mpa), 900psi (15.0Mpa), 1500psi (25.0Mpa), 2500psi (42.0Mpa).
b. Nominal diameter: 6mm~4000mm
c. Flange structure: strip welding, socket welding, threaded connection, loose sleeve, butt welding and flange cover
d. Flange sealing surface: concave surface, concave and convex surface, tongue and groove surface, metal ring connection surface

3) Japanese JIS pipe flange: It is generally only used for public works in petrochemical plants, has little influence internationally, and has not formed an independent system internationally.

4) China's national standard system for steel pipe flanges GB
1. Nominal pressure: 0.25Mpa~42.0Mpa
a. Series 1: PN1.0, PN1.6, PN2.0, PN5.0, PN10.0, PN15.0, PN25.0, PN42 (main series)
b. Series 2: PN0.25, PN0.6, PN2.5, PN4.0
Among them, PN0.25, PN0.6, PN1.0, PN1.6, PN2.5, PN4.0, a total of 6 grades of flange sizes belong to the European flange system represented by German flanges, and the rest are American flange systems represented by American flanges.
In the GB standard, the maximum nominal pressure level of the European flange system is 40Mpa, and the maximum nominal pressure level of the American flange system is 42Mpa.

2. Nominal diameter: 10mm~1500mm
3. Flange structure:
Integral flange
Unit flange
a. Threaded flange
b. Welding flange Butt welding flange
Neck flat welding flange Neck socket welding flange Plate flat welding flange
c. Loose flange Butt welding ring Loose neck flange Butt welding ring Loose plate flange Flat welding ring Loose plate flange Plate flip loose flange
d. Flange cover (blind hole flange)
e. Rotating flange
f. Anchor flange
g. Surfacing/covering flange

4. Flange sealing surface: flat surface, concave surface, concave and convex surface, tongue and groove surface, ring connection surface

Pipe flange production process:

The pipe flange production process is mainly divided into four types: casting, cutting, rolling and forging.

1. Casting flange: The flange is produced by fine casting. This type of casting is much finer than ordinary sand castings, and the quality has been greatly improved, such as loose arrangement, pores and other problems have been greatly improved. The production process includes putting the selected raw material steel into the medium frequency electric furnace for melting, so that the molten steel temperature reaches 1600-1700℃, preheating the metal mold to 800-900℃ and maintaining a constant temperature, starting the centrifuge, injecting the medium steel into the mold for preheating, and waiting until the casting is formed, and then cooling the process, and finally demolding and removing the casting.

2. Cutting flange: Cutting the flange line directly on the middle plate is a straight plane processing. The cut flange is very flat and does not require further processing, and can achieve a higher precision.

3. Rolling flange: Cut strips from the middle plate and then weld them into a circle, and then roll them into flanges. The flanges produced by this process are accurate in size and low in price, but require a long time and more labor.

4. Forged flange: During the forging process, the metal blank is placed in a mold and impacted or plastically deformed to obtain a flange of the desired shape and size. Forged flanges generally have lower carbon content than cast flanges and are less prone to rust. The forgings have better streamlines, denser structures, and better mechanical properties than cast flanges.

Read more: Pipe Flange Size Specifications or Pipe Flange Material Selection