Flange standard

A flange standard lays down the dimensions, surface finish, facing type, marking, material and technical specifications for flanges.

National flange standards in Europe have largely been superseded by the European EN 1092 series. It comprises flanges with DIN origin and PN/DN designations (DN classification being dependent on PN). Various national standards bodies have incorporated this standard into their respective national standards: DIN EN 1092; BS EN 1092 und NF EN 1092.

European standard EN 1092: Flanges and Their Joints (Circular Flanges for Pipes, Valves, Fittings and Accessories, PN designated)
  • Part 1: Steel flanges, PN 2.5 to PN 400
  • Part 2: Cast iron flanges, PN 2.5 to PN 63
  • Part 3: Copper alloy flanges, PN 6 to PN 40
  • Part 4: Aluminium alloy flanges, PN 10 to PN 63
British standards for flanges
  • BS EN 1092-1 (Cast steel flanges) for nominal pressures, see DIN EN 1092-1
  • BS EN 1092-2 (Cast iron flanges) for nominal pressures, see DIN EN 1092-2

A further European flange standard is EN 1759. This standard only features ANSI/ASME flanges (ASME B 16.5 1996 edition) with Class and NPS designations.

American standards for flanges
  • ASME B 16.1: Gray iron pipe flanges and flanged fittings (cast iron flanges, Classes 25, 125 and 250)
  • ASME B 16.5: Pipe flanges and flanged fittings: NPS 1/2 through NPS 24 Metric/Inch Standard; (Cast steel and weld-neck flanges Classes 150, 300, 400, 600, 900, 1500 and 2500)

In the EN 1092 standard, the numerical value in the PN designation is equal to the max. applicable pressure in bar at a reference temperature of 20 °C.

Class figure in American flange standards
  • For cast iron flanges, the figure in the Class designation is equal to the max.
    applicable pressure in psi at temperatures ranging from 66 to 232 °C depending on the class.
  • For steel and cast steel flanges, the figure in the class designation is equal to the max. applicable pressure in psi at temperatures ranging from 350 to 650 °C depending on the material.

At a temperature of 20 °C, the figure for the max. applicable pressure is therefore considerably higher than that designating the class, especially for steel and cast steel flanges.
Although PN designations are not used in American flange standards, they are matched with their equivalent pressure classes in ASME B 16.5-2003.

Flanges to ISO 7005 are internationally standardised. This standard series comprises DIN flanges (PN 2.5; 6; 10; 16; 25 and 40) and ASME flanges. This standard, however, also specifies DN and PN designations for ASME flanges (PN 20; 50; 110; 150; 250 and 420).

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