Flange Bolt Chart
Flange bolt charts specify the number of bolts, bolt diameter, and bolt length required for each combination of flange size and pressure class. These values are defined by ASME B16.5 for flanges from 1/2” to 24” and ASME B16.47 for flanges 26” and above. The standard bolting material is ASTM A193 B7 stud bolts with ASTM A194 2H heavy hex nuts.
Class 150 Flange Bolt Chart
| Flange Size | No. of Bolts | Bolt Diameter | Stud Length (RF) |
|---|---|---|---|
| 1/2” | 4 | 1/2” | 2-1/2” |
| 3/4” | 4 | 1/2” | 2-3/4” |
| 1” | 4 | 1/2” | 2-3/4” |
| 1-1/4” | 4 | 1/2” | 3” |
| 1-1/2” | 4 | 1/2” | 3-1/4” |
| 2” | 4 | 5/8” | 3-1/2” |
| 2-1/2” | 4 | 5/8” | 3-3/4” |
| 3” | 4 | 5/8” | 3-3/4” |
| 4” | 8 | 5/8” | 3-3/4” |
| 6” | 8 | 3/4” | 4-1/4” |
| 8” | 8 | 3/4” | 4-1/2” |
| 10” | 12 | 7/8” | 5” |
| 12” | 12 | 7/8” | 5-1/4” |
| 14” | 12 | 1” | 5-3/4” |
| 16” | 16 | 1” | 6” |
| 18” | 16 | 1-1/8” | 6-1/2” |
| 20” | 20 | 1-1/8” | 6-3/4” |
| 24” | 20 | 1-1/4” | 7-1/2” |
Class 300 Flange Bolt Chart
| Flange Size | No. of Bolts | Bolt Diameter | Stud Length (RF) |
|---|---|---|---|
| 1/2” | 4 | 1/2” | 3” |
| 3/4” | 4 | 5/8” | 3-1/4” |
| 1” | 4 | 5/8” | 3-1/2” |
| 1-1/4” | 4 | 5/8” | 3-1/2” |
| 1-1/2” | 4 | 3/4” | 4” |
| 2” | 8 | 5/8” | 3-3/4” |
| 2-1/2” | 8 | 3/4” | 4-1/4” |
| 3” | 8 | 3/4” | 4-1/2” |
| 4” | 8 | 3/4” | 4-3/4” |
| 6” | 12 | 3/4” | 5” |
| 8” | 12 | 7/8” | 5-1/2” |
| 10” | 16 | 1” | 6-1/4” |
| 12” | 16 | 1-1/8” | 6-1/2” |
| 14” | 20 | 1-1/8” | 7” |
| 16” | 20 | 1-1/4” | 7-1/2” |
| 18” | 24 | 1-1/4” | 7-3/4” |
| 20” | 24 | 1-1/4” | 8” |
| 24” | 24 | 1-1/2” | 9” |
Class 600 Flange Bolt Chart
| Flange Size | No. of Bolts | Bolt Diameter | Stud Length (RF) |
|---|---|---|---|
| 1/2” | 4 | 1/2” | 3” |
| 3/4” | 4 | 5/8” | 3-1/4” |
| 1” | 4 | 5/8” | 3-1/2” |
| 1-1/2” | 4 | 3/4” | 4” |
| 2” | 8 | 5/8” | 3-3/4” |
| 3” | 8 | 3/4” | 4-3/4” |
| 4” | 8 | 7/8” | 5-1/4” |
| 6” | 12 | 1” | 5-3/4” |
| 8” | 12 | 1-1/8” | 6-3/4” |
| 10” | 16 | 1-1/4” | 7-1/2” |
| 12” | 20 | 1-1/4” | 7-3/4” |
| 14” | 20 | 1-3/8” | 8-1/2” |
| 16” | 20 | 1-1/2” | 9” |
| 18” | 20 | 1-5/8” | 10” |
| 20” | 24 | 1-5/8” | 10-1/4” |
| 24” | 24 | 1-7/8” | 11-3/4” |
Class 900 and Above
As pressure class increases, bolt diameters and quantities grow significantly to handle higher gasket seating loads and hydrostatic end forces.
| Flange Size | Class 900 Bolts | Class 1500 Bolts | Class 2500 Bolts |
|---|---|---|---|
| 2” | 8 x 3/4” | 8 x 7/8” | 8 x 1” |
| 4” | 8 x 1-1/8” | 8 x 1-1/4” | 8 x 1-1/2” |
| 6” | 12 x 1-1/8” | 12 x 1-3/8” | 8 x 2” |
| 8” | 12 x 1-3/8” | 12 x 1-5/8” | 12 x 2” |
| 10” | 16 x 1-3/8” | 12 x 1-7/8” | 12 x 2-1/2” |
| 12” | 20 x 1-3/8” | 16 x 1-7/8” | 12 x 2-3/4” |
Bolt Length Calculation
Stud bolt length for a flanged joint equals the sum of: both flange thicknesses + gasket thickness + two nut heights + thread protrusion allowance (typically one thread pitch past each nut). Detailed stud bolt length calculations account for the actual flange dimensions from ASME B16.5 tables.
The total bolt torque required per bolt increases with bolt diameter and is specified in the project’s bolting torque charts.
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