In This Article
- 1.ASME B16.5 Scope and Pressure Classes
- 2.Class 150 Flange Dimensions (ASME B16.5)
- 3.Class 300 Flange Dimensions (ASME B16.5)
- 4.Class 600 Flange Dimensions (ASME B16.5)
- 5.Class 900 and Class 1500 Flange Dimensions
- 6.Class 2500 Flange Dimensions
- 7.Facing Types: Raised Face, Flat Face, and RTJ
- 8.Flange Bolt Tightening and Gasket Seating
ASME B16.5 Scope and Pressure Classes
ASME B16.5 (Pipe Flanges and Flanged Fittings: NPS 1/2" Through NPS 24") is the governing standard for flanged valve and pipe connections in pressure plant and pipeline service across North America and internationally. It defines seven pressure classes — Class 150, 300, 400, 600, 900, 1500, and 2500 — with dimensions, material groups, and pressure-temperature ratings. Class 400 is rarely used (it was added for legacy compatibility with ASME B16.1 cast iron flanges and is almost never specified for new valves). The standard covers: flange OD, raised face OD, bolt circle diameter, bolt size, number of bolts, flange thickness, hub bore, face-to-face dimensions, and facing finish requirements.
Class 150 Flange Dimensions (ASME B16.5)
| NPS (inch) | Flange OD (mm) | Bolt Circle (mm) | No. Bolts | Bolt Size | RF Bore (mm) | RF Height (mm) |
|---|---|---|---|---|---|---|
| 1/2" | 88.9 | 60.3 | 4 | M12 (1/2") | 35.1 | 1.6 |
| 3/4" | 98.6 | 69.8 | 4 | M12 (1/2") | 43.2 | 1.6 |
| 1" | 108.0 | 79.4 | 4 | M12 (1/2") | 51.1 | 1.6 |
| 1.5" | 127.0 | 98.4 | 4 | M12 (1/2") | 73.2 | 1.6 |
| 2" | 152.4 | 120.7 | 4 | M16 (5/8") | 91.9 | 1.6 |
| 3" | 190.5 | 152.4 | 4 | M20 (3/4") | 127.0 | 1.6 |
| 4" | 228.6 | 190.5 | 8 | M20 (3/4") | 157.2 | 1.6 |
| 6" | 279.4 | 241.3 | 8 | M20 (3/4") | 215.9 | 1.6 |
| 8" | 342.9 | 298.5 | 8 | M24 (7/8") | 269.7 | 1.6 |
| 10" | 406.4 | 362.0 | 12 | M24 (7/8") | 323.8 | 1.6 |
| 12" | 482.6 | 431.8 | 12 | M24 (7/8") | 381.0 | 1.6 |
| 14" | 533.4 | 476.3 | 12 | M27 (1") | 419.1 | 1.6 |
| 16" | 596.9 | 539.8 | 16 | M27 (1") | 469.9 | 1.6 |
| 18" | 635.0 | 577.9 | 16 | M30 (1.1/8") | 533.4 | 1.6 |
| 20" | 698.5 | 635.0 | 20 | M30 (1.1/8") | 584.2 | 1.6 |
| 24" | 812.8 | 749.3 | 20 | M30 (1.1/8") | 692.2 | 1.6 |
Class 300 Flange Dimensions (ASME B16.5)
| NPS (inch) | Flange OD (mm) | Bolt Circle (mm) | No. Bolts | Bolt Size | RF Bore (mm) |
|---|---|---|---|---|---|
| 1/2" | 95.3 | 66.7 | 4 | M12 (1/2") | 35.1 |
| 3/4" | 117.5 | 82.6 | 4 | M16 (5/8") | 43.2 |
| 1" | 123.8 | 88.9 | 4 | M16 (5/8") | 51.1 |
| 1.5" | 155.6 | 114.3 | 4 | M20 (3/4") | 73.2 |
| 2" | 165.1 | 127.0 | 8 | M16 (5/8") | 91.9 |
| 3" | 209.6 | 168.3 | 8 | M20 (3/4") | 127.0 |
| 4" | 254.0 | 200.2 | 8 | M24 (7/8") | 157.2 |
| 6" | 317.5 | 269.9 | 12 | M24 (7/8") | 215.9 |
| 8" | 381.0 | 330.2 | 12 | M27 (1") | 269.7 |
| 10" | 444.5 | 387.4 | 16 | M27 (1") | 323.8 |
| 12" | 520.7 | 450.8 | 16 | M30 (1.1/8") | 381.0 |
Class 600 Flange Dimensions (ASME B16.5)
| NPS (inch) | Flange OD (mm) | Bolt Circle (mm) | No. Bolts | Bolt Size | RF Bore (mm) |
|---|---|---|---|---|---|
| 1/2" | 95.3 | 66.7 | 4 | M12 (1/2") | 35.1 |
| 3/4" | 117.5 | 82.6 | 4 | M16 (5/8") | 43.2 |
| 1" | 123.8 | 88.9 | 4 | M16 (5/8") | 51.1 |
| 1.5" | 155.6 | 114.3 | 4 | M20 (3/4") | 73.2 |
| 2" | 165.1 | 127.0 | 8 | M16 (5/8") | 91.9 |
| 3" | 209.6 | 168.3 | 8 | M20 (3/4") | 127.0 |
| 4" | 273.1 | 215.9 | 8 | M24 (7/8") | 157.2 |
| 6" | 355.6 | 292.1 | 12 | M30 (1.1/8") | 215.9 |
| 8" | 419.1 | 349.3 | 12 | M33 (1.1/4") | 269.7 |
| 10" | 508.0 | 431.8 | 16 | M33 (1.1/4") | 323.8 |
| 12" | 558.8 | 489.0 | 20 | M33 (1.1/4") | 381.0 |
Class 900 and Class 1500 Flange Dimensions
| NPS | Class 900 OD (mm) | Class 900 BC (mm) | Class 900 Bolts | Class 1500 OD (mm) | Class 1500 BC (mm) | Class 1500 Bolts |
|---|---|---|---|---|---|---|
| 2" | 317.5 | 244.5 | 8 × M27 | 317.5 | 244.5 | 8 × M27 |
| 3" | 374.6 | 292.1 | 8 × M30 | 393.7 | 317.5 | 8 × M33 |
| 4" | 431.8 | 342.9 | 8 × M33 | 482.6 | 393.7 | 8 × M39 |
| 6" | 558.8 | 444.5 | 12 × M33 | 609.6 | 495.3 | 12 × M39 |
| 8" | 660.4 | 523.9 | 12 × M39 | 736.6 | 584.2 | 12 × M45 |
| 10" | 762.0 | 619.1 | 16 × M39 | 901.7 | 723.9 | 12 × M52 |
| 12" | 889.0 | 723.9 | 20 × M39 | 1036.3 | 838.2 | 16 × M52 |
Class 2500 Flange Dimensions
| NPS | Flange OD (mm) | Bolt Circle (mm) | No. Bolts | Bolt Size | RF Bore (mm) |
|---|---|---|---|---|---|
| 1/2" | 120.6 | 82.6 | 4 | M16 (5/8") | 22.4 |
| 3/4" | 130.3 | 95.3 | 4 | M16 (5/8") | 28.4 |
| 1" | 149.2 | 107.9 | 4 | M20 (3/4") | 34.5 |
| 1.5" | 193.7 | 146.0 | 4 | M27 (1") | 47.8 |
| 2" | 215.9 | 165.1 | 8 | M24 (7/8") | 62.0 |
| 3" | 279.4 | 215.9 | 8 | M27 (1") | 85.9 |
| 4" | 355.6 | 279.4 | 8 | M33 (1.1/4") | 107.9 |
| 6" | 482.6 | 393.7 | 8 | M39 (1.1/2") | 162.1 |
| 8" | 603.3 | 482.6 | 12 | M39 (1.1/2") | 203.2 |
| 10" | 730.3 | 584.2 | 12 | M45 (1.3/4") | 255.6 |
Facing Types: Raised Face, Flat Face, and RTJ
- Raised Face (RF): Standard facing for Classes 150–2500. The raised face protrudes 1.6 mm (Classes 150 & 300) or 6.4 mm (Classes 400–2500) above the bolt face. Gasket bears on the raised face only, concentrating seating stress. Most common valve connection facing.
- Flat Face (FF): No raised face — gasket covers full flange face. Required when mating flanges are made of brittle material (cast iron, ductile iron Class 125/250) where the raised face would crack the mating flange under bolt-up. Cannot be mixed with RF flanges.
- Ring-Type Joint (RTJ): A machined groove in the flange face accepts an oval or octagonal ring gasket (soft iron or SS 316 typically). Used for high-pressure, high-temperature services (Class 900 and above) and subsea connections where spiral wound gaskets would be unreliable. Tighter seal than RF at extreme pressures.
- Tongue and Groove (T&G), Male and Female (M&F): Specialised facings for jacketed piping and cryogenic service — not common in standard valve flanges.
Flange Bolt Tightening and Gasket Seating
Correct bolt torque is as critical as correct gasket selection. Under-torquing leaves the gasket unseated; over-torquing crushes the gasket beyond its design limit or yields the bolts. For standard spiral-wound gaskets with inner and outer rings (ASME B16.20), the seating stress is typically 55–70 MPa. Bolt torque = (T_target × d) / (K × d) where K is the nut factor (0.20 for lubricated B7 studs, 0.15 for PTFE-coated). Always torque in a cross-pattern (star sequence) to at least 3 passes, reaching full torque only on the final pass. Re-check bolt torque after first pressure application and first thermal cycle.
Vajra Industrial Solutions supplies valves with flanged ends per ASME B16.5 as standard for all carbon steel, stainless steel, and alloy steel valve bodies. Raised face is standard; RTJ and flat face are available on request. All flange dimensions are verified per latest ASME B16.5 edition. Contact sales@vajravyuh.com for valve specifications with specific flange class and facing requirements.
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