It mainly plays the role of connection. Therefore, the main characteristics of flange are the connection mode and sealing form. The dominant influencing parameter is the pipe pressure (different media affect the selection of material)

Low pressure system (PN < 2.5MPa) adopts flat welding or plate flange;

Common raised face (RF) seal, medium pressure system (2.5-64mpa) using butt welding flange;

RF or concave convex face (FM / M) seal, high pressure system (above 10.0MPa), usually using butt welding flange, ladder groove (RJ) seal;

In low pressure stainless steel system, loose flange or looper flange is sometimes used for cost saving and maintenance convenience.
Standard classification of flange

At present, there are many flange standards, such as GB (national standard), JB (standard of Ministry of machinery), Hg (standard of Ministry of chemical industry), ANSI (American Standard), JIS (Japanese standard), DIN (German standard) and so on.

However, the standards that are widely used are divided into two categories

European system based on DIN standard (including DIN, GB, JB, hg20592);

American system based on ANSI standard (including ANSI, GB, hg20615).

The two types of flange can be distinguished by the identification of flange pressure class（ JIS standard is a standard of another kind of system, and does not belong to this two kinds of system.)

1 European flange system

European flange system: DIN (including Soviet Union)

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, 40.0, MPa;

Common diameter: 15 ~ 600mm;

Flange structure types: flat welding plate, flat welding ring loose sleeve type, curling loose sleeve type, butt welding curling loose sleeve type, butt welding ring loose sleeve type, butt welding type, threaded connection type with neck, integral type and flange cover;

Flange sealing surface: plane, concave surface, concave convex surface, tenon surface, rubber ring connection surface, lens surface and diaphragm welding surface;

The standard of OCT pipe flange issued by the Soviet Union in 1980 is similar to the DIN standard of Germany.

2 American flange system

American flange system: American ANSI B16.5 "steel pipe flanges and flange fittings"

Nominal pressure: 150psi (2.0MPa), 300PSI (5.0mpa), 400psi (6.8mpa), 600psi (10.0MPa), 900psi (15.0mpa), 1500psi (25.0mpa), 2500psi (42.0mpa);

Common diameter: 6 ~ 4000 mm;

Flange structure type: strip welding, socket welding, threaded connection, loose sleeve, butt welding and flange cover;

Flange sealing surface: concave surface, concave convex surface, mortise surface, metal ring connection surface.

3jis pipe flange

JIS pipe flange: it is generally only used for public works in petrochemical plants, which has little influence in the world and has not formed an independent system in the world.

GB system

The national standard system of steel pipe flange in China is GB.

1. Nominal pressure: 0.25MPa ~ 42.0mpa

Series 1: PN1.0, pn1.6, pn2.0, pn5.0, pn10.0, pn15.0, pn25.0, pn42 (main series)

Series 2: pn0.25, pn0.6, pn2.5, pn4.0

Among them, the flange sizes of pn0.25, pn0.6, PN1.0, pn1.6, pn2.5 and pn4.0 belong to the European flange system represented by German flange, and the rest belong to the American flange system represented by American flange.

In GB standard, the maximum nominal pressure class of flange system in Europe is 4MPa, and the maximum nominal pressure class of flange system in America is 42MPa.

2. Nominal diameter: 10mm ~ 4000mm

3. Flange structure:

① Integral flange

② Unit flange

Threaded flange;

Welding flange, butt welding flange;

Flat welding flange with neck, socket welding flange with neck and plate flat welding flange: loose flange, loose neck flange with butt welding ring, loose plate flange with butt welding ring, loose plate flange with butt welding ring and plate over loose flange;

Flange cover (blind flange).

4. Flange sealing surface: plane, concave surface, concave convex surface, mortise surface, ring joint surface

Standard system of instrument pipe flange

1. DIN standard

Common pressure rating:

PN6，PN10，PN16，PN25，PN40，PN64，PN100，PN160，PN250

Flange sealing surface:

Raised face din2526c raised face flange

Grooved acc. din2512n

2. ANSI standard

Common pressure rating: cl150, cl300, cl600, cl900, cl1500

Flange sealing surface: ANSI B 16.5 RF flanges raised face flange

3. JIS standard: not commonly used

Common pressure rating: 10K, 20K