How DIN Flange Standards Are Organized
The DIN flange numbering system assigns a unique standard number to each combination of flange type and pressure class. Unlike the ASME system, where a single standard (B16.5) covers multiple flange types across all pressure classes, DIN uses separate documents for each variant. This means there are dozens of individual DIN flange standards rather than one consolidated reference.
Each standard defines the complete dimensional envelope for its scope: outside diameter, bolt circle diameter, number and size of bolt holes, flange thickness, hub dimensions (where applicable), and facing details. Material specifications are covered by separate DIN material standards that cross-reference the flange dimensional standards.
Understanding PN Pressure Ratings
PN stands for Pressure Nominal (from the French "Pression Nominale"). The number following PN represents the maximum allowable working pressure in bar at a reference temperature of 20 degrees Celsius. As operating temperature increases, the allowable working pressure decreases according to pressure-temperature curves defined in the standard.
| PN Rating | Pressure at 20°C (bar) | Approximate PSI | Typical Use |
|---|---|---|---|
| PN6 | 6 | ~87 | Low-pressure water, drainage |
| PN10 | 10 | ~145 | Water distribution, HVAC |
| PN16 | 16 | ~232 | General industrial, process water |
| PN25 | 25 | ~363 | Medium-pressure process piping |
| PN40 | 40 | ~580 | Higher-pressure industrial systems |
| PN64 | 64 | ~928 | High-pressure process applications |
| PN100 | 100 | ~1450 | High-pressure steam, chemical |
| PN160 | 160 | ~2321 | Severe-service applications |
| PN250 | 250 | ~3626 | Extreme pressure service |
| PN400 | 400 | ~5802 | Maximum pressure applications |
Important: PN ratings indicate pressure capacity at room temperature only. At elevated temperatures, the actual allowable working pressure is always lower than the PN number. Always consult the applicable pressure-temperature tables for your specific material and operating conditions.
Complete DIN Standard Number Reference
Weld Neck Flanges
| Standard | Pressure Class | Pressure Range (bar) |
|---|---|---|
| DIN 2630 | PN 1 and PN 2.5 | 1 - 2.5 |
| DIN 2631 | PN 6 | 6 |
| DIN 2632 | PN 10 | 10 |
| DIN 2633 | PN 16 | 16 |
| DIN 2634 | PN 25 | 25 |
| DIN 2635 | PN 40 | 40 |
| DIN 2636 | PN 64 | 64 |
| DIN 2637 | PN 100 | 100 |
| DIN 2638 | PN 160 | 160 |
| DIN 2628 | PN 250 | 250 |
| DIN 2629 | PN 320 | 320 |
| DIN 2627 | PN 400 | 400 |
Slip-On (Flat Welding) Flanges
| Standard | Pressure Class |
|---|---|
| DIN 2573 | PN 6 |
| DIN 2576 | PN 10 |
| DIN 2502 | PN 16 |
| DIN 2503 | PN 25 and PN 40 |
Blind Flanges
| Standard | Pressure Classes Covered |
|---|---|
| DIN 2527 | PN 6, 10, 16, 25, 40, 64, and 100 |
Threaded Flanges with Neck
| Standard | Pressure Class |
|---|---|
| DIN 2565 | PN 6 |
| DIN 2566 | PN 10 and PN 16 |
| DIN 2567 | PN 25 and PN 40 |
| DIN 2568 | PN 64 |
| DIN 2569 | PN 100 |
Lap Joint Flanges
| Standard | Pressure Class |
|---|---|
| DIN 2641 | PN 6 |
| DIN 2642 | PN 10 |
Loose Flanges with Collar/Ring
| Standard | Pressure Class |
|---|---|
| DIN 2652 | PN 6 |
| DIN 2653 | PN 10 |
| DIN 2655 | PN 25 |
| DIN 2656 | PN 40 |
The Transition to EN 1092-1
The European Committee for Standardization (CEN) developed EN 1092-1 as a harmonized European flange standard intended to consolidate and eventually replace the many individual DIN flange numbers. The EN standard covers circular steel flanges in PN designations from PN 2.5 through PN 400, and nominal sizes from DN 10 to DN 4000.
EN 1092-1 organizes flanges by "Type" number rather than by individual standard documents. For example, Type 11 in EN 1092-1 corresponds to weld neck flanges (previously covered by DIN 2631 through DIN 2638), and Type 01 corresponds to plate flanges (replacing DIN 2573 and DIN 2576).
In practice, both systems remain in active use. Many existing facilities, maintenance procedures, and procurement specifications still reference the original DIN numbers. The transition is happening gradually as new projects adopt the EN standard while existing installations continue to use DIN designations for replacement parts and maintenance.
Compatibility note: Most dimensions in EN 1092-1 match their DIN predecessors. However, there are specific exceptions. A well-known one is the DN65 PN16 flange: the original DIN 2501/2633 specification calls for 4 bolt holes with M16 bolts, while EN 1092-1 specifies 8 bolt holes with M16 bolts for the same size and pressure class. Always verify the exact standard being referenced before ordering replacement components.
Nominal Size (DN) System
DIN flanges use the DN (Diametre Nominal) system for sizing, which is a metric designation that roughly corresponds to the internal diameter of the pipe in millimeters. Common DN sizes include DN10, DN15, DN20, DN25, DN32, DN40, DN50, DN65, DN80, DN100, DN125, DN150, DN200, DN250, DN300, DN350, DN400, DN450, DN500, DN600, DN700, DN800, DN900, and DN1000.
The DN number is not an exact measurement but rather a nominal designation used for reference purposes. The actual bore dimension of a flange depends on both the DN size and the pipe schedule or wall thickness being used.