I. Overview of Flange Connection Basics and Standard Systems

Flange connection is a combined sealing structure composed of flanges, gaskets, and bolts interconnected, belonging to detachable connections. Pipeline flanges refer to flanges used for piping in pipeline installations; when used on equipment, they refer to the inlet and outlet flanges of the equipment.

Internationally, pipe flange standards are mainly divided into the European flange system and the American flange system. The Japanese JIS standard has relatively little international influence and has not formed an independent system. China's national standard for steel pipe flanges (GB) simultaneously covers parts of both major systems.

II. Commonly Used International Pipe Flange Standard Systems

1. European Flange System (German DIN, including Soviet standards)

The European flange system is represented by the German DIN standard. The OCT pipe flange standard issued by the Soviet Union in 1980 is similar to the DIN standard and will not be further described. Its core parameters are as follows:

  • 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
  • Nominal diameter: 15~600 mm
  • Structural types: flat welding plate type, flat welding ring loose sleeve type, curled edge loose sleeve type, butt welding curled edge loose sleeve type, butt welding ring loose sleeve type, butt welding type, neck threaded connection type, integral type, and flange cover
  • Sealing faces: flat face, concave face, male and female face, tongue and groove face, rubber ring connection face, lens face, and diaphragm welding face

2. American Flange System (American ANSI B16.5)

The American flange system is represented by American ANSI B16.5 "Steel Pipe Flanges and Flanged Fittings" and is widely used in petrochemical and other fields. Its main parameters are:

  • Nominal pressure: 150 psi (2.0 MPa), 300 psi (5.0 MPa), 400 psi (6.8 MPa), 600 psi (10.0 MPa), 900 psi (15.0 MPa), 1500 psi (25.0 MPa), 2500 psi (42.0 MPa)
  • Nominal diameter: 6~4000 mm
  • Structural types: strip welding, socket welding, threaded connection, loose sleeve, butt welding, and flange cover
  • Sealing faces: concave face, male and female face, tongue and groove face, metal ring connection face

3. Japanese JIS Pipe Flanges

Japanese JIS pipe flanges are generally used only for utility services in petrochemical plants, have relatively little international influence, and have not formed an independent system.

III. China's National Standard System for Steel Pipe Flanges (GB)

China's GB standard system integrates the two major systems of Europe and America. The specific parameters are as follows:

1. Nominal Pressure

The nominal pressure range is 0.25 MPa~42.0 MPa, divided into two series:

  • Series 1 (main series): PN1.0, PN1.6, PN2.0, PN5.0, PN10.0, PN15.0, PN25.0, PN42
  • Series 2: PN0.25, PN0.6, PN2.5, PN4.0

Among them, the flange dimensions of the six ratings PN0.25, PN0.6, PN1.0, PN1.6, PN2.5, and PN4.0 belong to the European flange system represented by German flanges, and the rest belong to the American flange system represented by American flanges. In the GB standard, the maximum nominal pressure rating belonging to the European system is 4 MPa, and the maximum nominal pressure rating belonging to the American system is 42 MPa.

2. Nominal Diameter

The nominal diameter range is 10 mm~4000 mm.

3. Flange Structural Forms

Flange structural forms are divided into two major categories: integral flanges and unit flanges:

  • Integral flange
  • Unit flange:
    • Threaded flange
    • Welding flange: butt welding flange, neck flat welding flange, neck socket welding flange, plate flat welding flange
    • Loose sleeve flange: butt welding ring loose sleeve neck flange, butt welding ring loose sleeve plate flange, flat welding ring loose sleeve plate flange, plate type turned-over loose sleeve flange
    • Flange cover (blind flange)

4. Flange Sealing Faces

Sealing face types include: flat face, concave face, male and female face, tongue and groove face, ring joint face.

IV. Summary and Selection Recommendations

When selecting flanges, it is necessary to determine whether to use the European system or the American system according to the pressure rating, diameter, medium characteristics, and connection requirements of the equipment or pipeline, and to match the corresponding structural type and sealing face. China's GB standard provides a flexible integrated solution. It is recommended that engineering technical personnel and procurement personnel make selections according to specific project specifications.