What is a PN flange?
PN stands for “Pressure Nominale”. The numerical value written after PN specifies the flange’s Max. applicable pressure in bar, at a reference temperature of 20 °C. For e.g., the cold working pressure of PN10 flanges roughly equates to 10 bar, PN16 to 16 bar and so on. Simply said it’s a classification system for flanges mostly used in European standards for installations in European countries.
Another designation “DN” stands for Diameter Nominale which is used with the term PN to specify the size of flange. DN is rough translation of imperial sizes in metric. So a 2” (which is 2 x 25.4=50.8mm) imperial flange stated as DN50, 12″ flange as DN300 and so on.
American standards such as ASME B16.5, ASME B16.47, and MSS SP-44 classify flanges according to pressure classes such as 150#, 300# etc and their dimensions are in inches. These are mainly used in USA but now it has become the foremost standard for flanges worldwide. In similar line European countries mostly install flanges according to standard DIN EN 1092-1, Which uses the above said PN/DN system to classify the flanges and the dimensions are in metric.
History of PN flanges
These flanges have a DIN origin which used to specify flanges with PN/DN designations (DN classification being dependent on PN). EN 1092 evolved from DIN 2501 which became part of ISO 7005, then EN 1092 was created as the standard for DIN based flanges.
DIN stands for "Deutsches Institut für Normung", meaning "German institute for standardisation".
National flange standards in Europe now have largely been superseded by the European EN 1092 series. Various national standards bodies have incorporated this standard into their respective national standards, such as DIN EN 1092; BS EN 1092 und NF EN 1092 etc.
Standard for PN flanges
You can find a PN Flanges specified in below standards
- 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
2. 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
3. international standards for flanges
ISO 7005 also includes European DIN flanges PN6 / 10 / 16 / 25 / 40 which were previously DIN 2501-1 and BS4504. These flanges are the same as EN1092 but EN1092 also includes higher rated DIN based flanges.
4. DIN standards for flanges (Per below pic)
Available Size and Types for PN flanges (per EN1092 std):
EN1092 has PN designations from PN 2,5 to PN 400 and nominal sizes from DN 10 to DN 4000. Types of flanges, Types of collars and Face types for flanges as per EN 1092-1 can be seen in pdf below.
SAIDI_Pipes_Fittings_Flanges_eng-36Compatibility of PN/ EN1092 flanges with ASME flange
Flanges developed to ANSI, AWWA, ASA or old British specifications measured in inches will not necessarily fit with the specification of PN flanges. Flanges those are from EN1092 standard will not match with corresponding ASME flanges for same pressure range.
However, the PN flanges from ISO 7005 can be used in where required which is interchangeable with ASME 16.5. For more information on it the following sentence is copied from ISO 7005 Standard which states-
ISO 7005 is based on the American and European steel flange system combined with some changes to the dimensions specified in the two system. PN20, PN50, PN110, PN150, PN260 and PN420 steel flanges are designed to be interchangeable with flanges to American standards ANSI/ASME B16.5 and MSS SP44. They are not identical but are deemed to comply with dimensions specified in ANSI/ASME B16.5 and MSS SP44 as appropriate.
In the American system flanges are designated by class ratings, but in European standards the flanges are designated in nominal pressure (PN) . The equivalent of PN designation to that of ASME/ANSI class rating are specified as in below table.
| Piping class ratings based on ASME B16.5 and corresponding PN rating | |||||||
|---|---|---|---|---|---|---|---|
| Flange Class | 150 | 300 | 400 | 600 | 900 | 1500 | 2500 |
| Flange Pressure Nominal, PN | 20 | 50 | 68 | 100 | 150 | 250 | 420 |
The equivalent of DN size designation per EN1092 to that of NB sizes as per ASME /ANSI standards are specified in below table.
| NB | DN | NB | DN | NB | DN | NB | DN |
|---|---|---|---|---|---|---|---|
| 1/2" | DN15 | 2 1/2" | DN65 | 10" | DN250 | 24" | DN600 |
| 3/4" | DN20 | 3" | DN80 | 12" | DN300 | 28" | DN700 |
| 1" | DN25 | 4" | DN100 | 14" | DN350 | 30" | DN750 |
| 1 1/4" | DN32 | 5" | DN125 | 16" | DN400 | 32" | DN800 |
| 1 1/2" | DN40 | 6" | DN150 | 18" | DN450 | 36" | DN900 |
| 2 | DN50 | 8" | DN200 | 20" | DN500 |
Material for PN flanges (EN1092 std):
The materials that can be used to manufacture the flanges are given in table-9 of EN-1092 STD. basically all common material like carbon steel, alloy steel, stainless steel and low temp carbon steel are available in European material standards.
Gasket for PN flanges (EN1092 std):
Appropriate gaskets for EN1092 PN flanges are covered in EN 1514 std.
Bolting for PN flanges (EN1092 std):
selection of bolting, to be done as per EN 1515-4, for combination of the materials of flanges and bolting see EN 1515-2.
