Flange standards

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National flange standards in Europe have largely been superseded by the European EN 1092 series.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: Aluminum alloy flanges, PN 10 to PN 63

The International System (SI) metric equivalent of British units are shown throughout this topic:
NPS (Nominal Pipe Size) = DN* (Nominal Diameter)
Operating Pressure Class = PN* (Pressure Number)

Many countries in the European Union (EU) mainly install flanges to the DIN EN 1092-1 (forged stainless or steel flanges).
This standard is very similar to the ASME flange standard. The EN 1092-1 standard incorporates a threaded flange to IOS7.1 instead of NPT. The different forms of flanges within the EN 1092-1 (European Norm Euro norm) is indicated within the flange name through the type. Different types of flanges have different standards, some are as follow:

TYPE OF FLANGE	EN STANDARD	DIN STANDARD
Blind Flange	Type 5	DIN 2527
Threaded Flange	Type 12	DIN 2558, 2565 – 2569
Weld Neck Flange	Type 11	DIN 2627 – 2638
Flat Flange	Type 1	DIN 2573, 2578
Lapped Flange	Type 2, 4	DIN 2641, 2622, 2655, 2656

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.

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), this includes pressure ratings, dimensions, tolerances, materials, marking, and testing.
• ASME B 16.47: Pipe flanges and flanged fittings: NPS 26 through NPS 60 Metric/Inch Standard; (Classes 75, 150, 300, 400, 600, and 900). Then, ASME B16.47 is further divided into ASME B16.47 Series A and ASME B16.47 Series B flanges for Blinds and Weld-necks.

The following MSS, API and AWWA standards are written to supplement B16.5:
MSS SP-6: Flange facings
MSS SP-9: Spot facing for bronze, iron and steel flanges
MSS SP-25: Marking of flanges
MSS SP-39: Bolts and nuts for flanges
API6A: Wellhead equipment
AWWA C207: Hub flanges

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 standardized. 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).

WHAT IS THE DIFFERENCE BETWEEN ASME B16.47 SERIES A AND SERIES B FLANGES?

ASME B16 47 Series A flanges are thicker, heavier and stronger than their Series B counterparts. They also can often handle more external loading than Series B. Series A flanges tend to be more costly than Series B flanges. ASME B16.47 Series B flanges need more but smaller fasteners, such as bolts & nuts. They also usually have a smaller bolt circle diameter than Series A flanges. Generally, there is less flange movement after installation due to the smaller bolt circle diameter. Both Series A and B define weld neck flanges and blind flanges in raised face type. However, Series A defines ring type joint (RTJ) flanges from Class 300 through Class 900 within this standard while Series B does not.

Series A flanges are popular for new pipeline projects or equipment. Meanwhile, many choose Series B flanges for refurbishment or replacement jobs.