Last updated: April 2026 — based on ASME PCC-1 Appendix J
Calculate the nominal bolt-up torque for a flanged joint given your gasket seating stress, bolt size, bolt grade, and lubrication. Output is the torque per bolt that produces the required preload, following the T = K · F · d torque–preload relationship used in ASME PCC-1 Appendix J.
Inputs
Result
Calculated as T = K · F · d where K is the nut factor for the selected lubricant, F is the required preload (target stress × tensile stress area), and d is the nominal bolt diameter. Values are nominal; always verify against the flange designer's bolt-up procedure and ASME PCC-1 for critical service.
How the Calculation Works
The torque–preload relationship for a threaded fastener can be derived rigorously from thread geometry and under-head friction, but in practice ASME PCC-1 Appendix J reduces it to a single empirical constant — the nut factor K:
T = K × F × d- T = installation torque (N·m)
- K = nut factor — dimensionless friction coefficient depending on lubrication and thread condition
- F = bolt preload (N) = target stress × tensile stress area (At) of the bolt
- d = nominal bolt diameter (m)
Typical Nut Factor (K) Values
| Condition | K | Notes |
|---|---|---|
| Dry / as-received steel threads | 0.20 | Default when no lubricant is specified. Scatter ±25 %. |
| Machine oil / general lubricant | 0.18 | Light oil on threads and under-head. |
| Moly disulphide / anti-seize (nickel-based) | 0.16 | Most common refinery spec. |
| PTFE / teflon-based anti-seize | 0.13 | Very low friction — use cautiously; easy to over-preload. |
| Copper-based anti-seize | 0.17 | Good for high temperature. |
When Should I Adjust Target Bolt Stress?
- 50 % of yield — default for new joints with new bolts, per ASME PCC-1.
- 40 % of yield — for flanges that will see thermal cycling, or soft gaskets (PTFE, rubber) that cannot tolerate over-compression.
- 60–70 % of yield — only with qualified bolts, tension-controlled tightening, and engineering sign-off.
- 30 % of yield — re-used flanges with relaxed gaskets, or cast-iron flanges that cannot carry full bolt load.
Bolt-Up Procedure
Follow ASME PCC-1 Section 7 for any critical flange:
- Clean flange faces and check for damage. Replace the gasket (never re-use).
- Lubricate bolt threads and under the nut face with the specified anti-seize.
- Hand-tighten all bolts, then snug-torque in a star pattern to ~30 % of target.
- Second pass: star pattern to ~60 % of target.
- Third pass: star pattern to 100 % of target.
- Final pass: rotational (clockwise) at 100 % target until no nut moves.
- For critical service, re-tighten after 24 hours (or one thermal cycle) to recover any relaxation.
Frequently Asked Questions
The T = K · F · d relationship is an empirical approximation. Real-world scatter is ±25 % or more driven mainly by the nut factor K, which varies with lubricant condition, thread cleanliness, and under-head friction. For critical service, use tension-controlled methods (hydraulic tensioning, ultrasonic measurement) rather than torque.
At 50 % of yield the bolt retains elastic reserve for residual load after relaxation, thermal cycling, and gasket creep — and leaves margin against the preload scatter inherent in torque-controlled tightening. Going higher is possible but only with qualified bolts, accurate measurement, and engineering sign-off per ASME PCC-1.
Yes — the target stress is the same; the joint has simply lost some preload through relaxation. Re-tighten with the same procedure (star pattern, three passes at 30/60/100 % of target, final rotational pass) using fresh lubricant if threads have been loosened.
Indirectly — the gasket dictates the required seating stress. A soft-faced gasket needs less; a spiral wound gasket with graphite filler typically needs about 175 MPa seating stress. You then size the bolt preload to deliver that stress over the gasket contact area, which is what this calculator converts to torque. See ASME VIII m & y factor tables for specific gasket-type stress requirements.
Related Tools & Guides
Sources & Standards
- ASME PCC-1-2019 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly, Appendix J.
- ASME B16.5 — Pipe Flanges and Flanged Fittings (bolt dimensions).
- Bickford, J. H. — Introduction to the Design and Behavior of Bolted Joints, 4th ed. (CRC Press) for K-factor tables.