Flange Bolt Torque Calculator
Calculate the tightening torque for a flange bolt from its nominal diameter and target preload, using the standard short-form equation.
Method
K = nut factor (0.20 dry, ~0.16 lubricated), F = bolt preload (N), d = nominal bolt diameter (m). Lubrication lowers K and the required torque for the same preload.
Nut factor K
| Condition | K |
|---|---|
| Dry / as-received | 0.20 |
| Lightly oiled | 0.18 |
| Moly / PTFE lubricated | 0.12–0.16 |
Frequently Asked Questions
How do I calculate bolt torque?
Use T = K × F × d, where K is the nut factor, F the target preload, and d the bolt diameter.
What is the nut factor K?
An empirical friction factor: about 0.20 dry and 0.12–0.16 lubricated.
Why does lubrication matter?
Lubrication reduces friction, so less torque achieves the same bolt preload — using a dry K on lubricated bolts over-tightens them.
How do I pick the preload?
Typically 50–75% of the bolt’s proof load; follow the flange/gasket assembly spec (e.g. ASME PCC-1).
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