1. Overview of Both Standards
Both standards define dimensions, materials, pressure-temperature ratings, and marking requirements for forged steel flanges. They are not interchangeable — bolt patterns, facing dimensions, and material specifications differ. Understanding these differences is essential for international projects where equipment from multiple regions must be integrated.
2. Size & Unit Systems
NPS vs DN — Nominal Pipe Size Designation
| ASME B16.5 (NPS) | EN 1092-1 (DN) | Approx. OD (mm) | Notes |
|---|---|---|---|
| 1/2" | DN 15 | 21.3 | Sizes align closely |
| 1" | DN 25 | 33.4 | — |
| 2" | DN 50 | 60.3 | — |
| 4" | DN 100 | 114.3 | — |
| 6" | DN 150 | 168.3 | — |
| 10" | DN 250 | 273.0 | Note: DN 250 ≠ 10" exactly |
| 12" | DN 300 | 323.9 | — |
⚠️ Dimensional Reference
NPS and DN numbers are nominal — they don't correspond to exact dimensions. A 6" (DN 150) flange has an OD that fits 6" nominal pipe (168.3 mm actual OD for STD wall), not 6 inches (152.4 mm). Always check the actual pipe OD schedule when specifying flanges.
3. Pressure Rating Systems
Class vs PN — Rating Designation
| ASME Class | Approx. PN Equiv. | Rating at 38°C (bar) | Notes |
|---|---|---|---|
| Class 150 | ~ PN 20 | 19.6 bar (CS) | Lowest rating; common for utility piping |
| Class 300 | ~ PN 50 | 51.1 bar (CS) | Most common for process piping |
| Class 600 | ~ PN 100 | 102.1 bar (CS) | High-pressure process |
| Class 900 | ~ PN 150 | 153.3 bar (CS) | Very high pressure |
| Class 1500 | ~ PN 250 | 255.1 bar (CS) | High-pressure steam, hydraulics |
| Class 2500 | ~ PN 420 | 425.4 bar (CS) | Highest standard rating |
⚠️ Temperature Derating
The ~PN equivalents above are for ambient temperature (38°C / 100°F). ASME B16.5 uses interpolation tables — ratings decrease continuously with temperature. EN 1092-1 uses fixed pressure-temperature tables by material group. At elevated temperatures (200-400°C), the ratings diverge. Always use the specific table from the applicable standard; never assume equivalence at design conditions.
4. Key Dimensional Comparison
Example: 6" (DN 150) Weld Neck Flange, Class 150 vs PN 16
| Dimension | ASME B16.5 Class 150 | EN 1092-1 PN 16 | Difference |
|---|---|---|---|
| Outside Diameter (OD) | 349.3 mm | 340 mm | +9.3 mm |
| Bolt Circle Diameter (BC) | 298.5 mm | 295 mm | +3.5 mm |
| Number of Bolts | 8 | 8 | Same |
| Bolt Hole Diameter | 22.2 mm (7/8") | 22 mm | ~Same |
| Raised Face Diameter | 269.9 mm | 273 mm | -3.1 mm |
| Raised Face Height | 2 mm | 2 mm | Same |
The dimensional differences above show why ASME and EN flanges cannot be bolted together directly in most cases. Even when bolt circle and hole count match, the outside diameter and raised face diameter differ enough to prevent proper gasket seating. Use a spacer/spool and match flanges of the same standard on each side.
5. Material Grade Equivalency
| Material Type | ASME B16.5 Grade | EN 1092-1 Grade | Material No. |
|---|---|---|---|
| Carbon Steel | ASTM A105 / A105N | P245GH / P250GH | 1.0352 / 1.0460 |
| Carbon Steel (Low Temp) | ASTM A350 LF2 | P255QL2 | 1.1104 |
| Cr-Mo Alloy (1.25Cr-0.5Mo) | ASTM A182 F11 | 13CrMo4-5 | 1.7335 |
| Cr-Mo Alloy (2.25Cr-1Mo) | ASTM A182 F22 | 10CrMo9-10 | 1.7380 |
| SS 304 | ASTM A182 F304 | X5CrNi18-10 | 1.4301 |
| SS 316L | ASTM A182 F316L | X2CrNiMo17-12-2 | 1.4404 |
| Duplex 2205 | ASTM A182 F51 | X2CrNiMoN22-5-3 | 1.4462 |
| Super Duplex 2507 | ASTM A182 F53 | X2CrNiMoN25-7-4 | 1.4410 |
💡 Chemical Equivalence ≠ Design Equivalence
While chemical composition and mechanical properties of equivalent grades are similar, they are not identical. Pressure-temperature ratings are calculated using different design margins in ASME vs EN. For code compliance, use the grade specified by the applicable standard — don't substitute without engineering review.
6. Flange Facing Types
| Facing Type | ASME B16.5 Designation | EN 1092-1 Designation | Notes |
|---|---|---|---|
| Raised Face | RF (default for Class 150-600) | Type B | Dimensions differ slightly; RF height = 2mm (ASME) vs 1-2mm (EN) |
| Flat Face | FF (standard on Class 125 cast iron) | Type A | No raised face; full-face gasket |
| Ring Type Joint | RTJ (Class 600+ high-pressure) | Type D | Groove dimensions differ; RTJ gaskets not interchangeable |
| Tongue & Groove | T&G (small / large) | Type C | Mating pairs required; dimensions differ |
7. Bolting Patterns & Bolt Hole Tolerances
EN 1092-1 typically specifies bolt holes 2 mm larger than the nominal bolt diameter (e.g., M20 bolt → 22 mm hole). ASME B16.5 uses fractional/inch-based hole sizes that, when converted to metric, are often slightly smaller. The larger EN holes provide more assembly tolerance but require appropriate gasket alignment.
| Bolt Size | ASME B16.5 Hole | EN 1092-1 Hole | Difference |
|---|---|---|---|
| M16 / 5/8" | 17.5 mm | 18 mm | +0.5 mm |
| M20 / 3/4" | 20.6 mm | 22 mm | +1.4 mm |
| M24 / 7/8" | 22.2 mm | 26 mm | +3.8 mm |
8. Can ASME and EN Flanges Be Used Together?
⚠️ General Answer: No
ASME B16.5 and EN 1092-1 flanges are not designed to be bolted together. While DN/NPS sizes often correspond, bolt circle diameters, raised face dimensions, and bolt hole patterns differ enough that direct assembly results in poor gasket sealing, uneven bolt loading, and potential joint failure.
If you must connect equipment with different flange standards:
- Use a transition spool — One end machined to ASME, the other to EN, welded in the middle. This is the standard approach for interfacing European and American equipment.
- Use a flange adapter / Lap Joint configuration — A stub end welded to the pipe with a loose lap joint flange that matches the opposing flange standard.
- Specify a weld neck flange with custom machining — Some manufacturers can machine the facing and bolt pattern to match a different standard, but this is a custom item with longer lead time.
9. Frequently Asked Questions
Can ASME B16.5 and EN 1092-1 flanges be used together?
Generally no. Bolt circle diameters, bolt hole sizes, and raised face dimensions often differ. For example, a DN 150 / 6" Class 150 flange has a 298.5mm bolt circle, while PN 16 has 295mm — close but not identical. Use a transition spool or specify matching standards on each side of the connection.
What is the pressure rating equivalent of Class 150?
At ambient temperature (38°C), ASME Class 150 ≈ PN 20 (19.6 bar for carbon steel). However, the standards use different temperature derating methods, and ratings diverge at elevated temperatures. Always use the specific rating table from the applicable standard for design.
Which standard should I use for my project?
Use ASME B16.5 for ASME B31.3, ASME BPVC, or API-based projects (North America, Middle East, global O&G). Use EN 1092-1 for EN 13480 or PED-compliant projects (EU, parts of Asia/Africa). In China, GB/T and HG/T standards are common; JIAJI FORGING manufactures to all three.
What are the key dimensional differences?
Key differences: (1) Units — ASME uses inches, EN uses mm, (2) Size designation — NPS vs DN, (3) Pressure rating — Class vs PN, (4) Bolt hole diameter — EN typically 2mm larger, (5) Raised face — dimensions differ slightly. Never assume interchangeability without checking dimensional tables.
Need Flanges to ASME or EN Standards?
JIAJI FORGING manufactures forged flanges to ASME B16.5, EN 1092-1, and GB/T standards with full certification.