DIN and ANSI represent the two dominant flange standardization systems in global industry. DIN originates from the German Institute for Standardization and uses metric measurements, while ANSI (American National Standards Institute) works within the imperial system. These are fundamentally different engineering frameworks, and understanding their distinctions is essential for anyone working with international piping systems.
The bottom line: DIN and ANSI flanges cannot be bolted together. They differ in bolt hole count, bolt circle diameter, flange thickness, facing profile, and pressure rating methodology. Even when a DIN flange and an ANSI flange are designated for the same nominal pipe size, they will not mate.
Measurement Systems
ANSI flanges are dimensioned in inches. Pipe sizes are designated in NPS (Nominal Pipe Size), and all linear measurements including outside diameter, bolt circle, hole diameter, and thickness are expressed in inches or fractions of inches.
DIN flanges are fully metric. Pipe sizes use the DN (Diametre Nominal) system in millimeters, and every dimensional specification is in millimeters. This difference runs through every aspect of the flange, from the bolt holes to the gasket seating surface.
Pressure Rating Approaches
ANSI uses a class-based system. The standard pressure classes are 150, 300, 600, 900, 1500, and 2500. These numbers do not directly represent pressure in any unit; they are designations that correspond to specific pressure-temperature curves defined in ASME B16.5.
DIN uses the PN (Pressure Nominal) system, where the number represents the maximum working pressure in bar at 20 degrees Celsius. Common PN ratings include PN6, PN10, PN16, PN25, PN40, PN64, PN100, and higher.
Approximate Equivalences
| ANSI Class | Approximate DIN PN | Notes |
|---|---|---|
| Class 150 | PN 20 (between PN16 and PN25) | Not a direct match; dimensions differ |
| Class 300 | PN 50 (between PN40 and PN64) | Approximate pressure equivalence only |
| Class 600 | PN 100 | Closest alignment of the common ratings |
| Class 900 | PN 150 | Rough equivalence |
| Class 1500 | PN 250 | Rough equivalence |
| Class 2500 | PN 420 | Rough equivalence |
Warning: These equivalences are for general reference when discussing pressure capacity. They do not mean the flanges are dimensionally compatible. A PN16 DIN flange and a Class 150 ANSI flange may handle similar pressures, but they absolutely cannot be bolted to each other.
Bolt Hole Patterns
This is where the incompatibility becomes physically obvious. For the same nominal pipe size, DIN and ANSI flanges typically specify different bolt circle diameters, different numbers of bolt holes, and different bolt sizes.
Consider a 2-inch (DN50) flange as an example. The ANSI Class 150 version has a bolt circle diameter of 4.75 inches (120.65 mm) with 4 bolt holes sized for 5/8-inch bolts. The DIN PN16 version (DIN 2633) for DN50 has a bolt circle diameter of 125 mm with 4 bolt holes sized for M16 bolts. Even though both have 4 bolt holes, the bolt circle is different, the hole diameter is different, and the overall flange diameter is different.
Physical Dimensions
DIN flanges tend to be thinner than their ANSI counterparts for comparable pressure ratings. ANSI flanges compensate with heavier construction, which reflects different design philosophies and safety factor approaches between the two standards bodies.
The outside diameters also differ. A DN100 DIN flange and a 4-inch ANSI flange serve the same nominal pipe size but have different outside diameters, different raised face dimensions, and different gasket seating areas.
Material Specifications
ANSI flanges reference ASTM and ASME material standards. The most common carbon steel grade is ASTM A105 for forged flanges, with A350 for low-temperature service and various 300-series stainless grades for corrosion resistance.
DIN flanges reference European material standards. Common carbon steel grades include P235GH and P250GH, while stainless steel grades use designations like 1.4301 (equivalent to 304) and 1.4401 (equivalent to 316). The underlying metallurgy is often similar, but the testing requirements, certification procedures, and acceptance criteria can differ between the two systems.
Face Types
Both DIN and ANSI flanges use raised face (RF) and flat face (FF) configurations. ANSI also defines ring-type joint (RTJ) faces for high-pressure applications. DIN uses face types designated as Form B (raised face), Form C (tongue and groove), and Form D (specific raised face variant).
The raised face height differs between the systems. ANSI Class 150 and 300 flanges have a standard 1/16-inch (1.6 mm) raised face, while DIN flanges typically have a 2 mm raised face. This difference affects gasket selection and seating behavior.
Summary Comparison
| Characteristic | DIN | ANSI |
|---|---|---|
| Origin | Germany (Europe) | United States |
| Measurement | Metric (mm, bar) | Imperial (inches, psi) |
| Pipe Sizing | DN (Diametre Nominal) | NPS (Nominal Pipe Size) |
| Pressure Rating | PN (bar at 20°C) | Class (150, 300, 600...) |
| Primary Standard | DIN 2501 series / EN 1092-1 | ASME B16.5 / B16.47 |
| Dominant Region | Europe, parts of Asia & S. America | North America |
| Flange Thickness | Generally thinner | Generally heavier |
| Raised Face Height | 2 mm typical | 1.6 mm (1/16") typical |
| Material Standards | EN / DIN (P235GH, 1.4301) | ASTM / ASME (A105, A182) |
| Interchangeable? | No. Never. | |
When You Encounter Both Systems
The most common real-world scenario involving both DIN and ANSI flanges is when a North American facility operates equipment imported from Europe, or when a European project uses components sourced from American suppliers. In these cases, adapter flanges or transition pieces are manufactured to bridge the two systems. These adapters have a DIN bolt pattern on one face and an ANSI pattern on the other, allowing a proper bolted connection between otherwise incompatible components.
The alternative is to replace the mismatched component entirely with one that conforms to the same standard as the rest of the system. In many situations, sourcing a DIN-compliant replacement part is simpler and more reliable than trying to adapt between standards.