The Torque-Tension Problem Explained
The fundamental equation: T = K × d × F (Torque = Nut Factor × Bolt Diameter × Target Tension). K varies from 0.10 (PTFE coated) to 0.25 (rusty plain steel), meaning the same torque at K=0.10 delivers 2.5× the bolt tension as K=0.25. Controlling K — through surface finish selection — is as important as bolt grade selection.
ASME PCC-1 Joint Assembly
Key requirements for compliant joint assembly:
- Certified bolting technicians (Level II per ASME PCC-1 Appendix A)
- Calibrated torque tools (±4% accuracy)
- Cross-bolting pattern (sequential, minimum 4 passes)
- Final torque pass at 100% target value
- Documented assembly records
Friction Coefficient Data for LOKRON Coatings
| Surface Finish | K Factor Range | Notes |
|---|---|---|
| Plain (as-machined) | 0.15–0.20 | Variable — not recommended for critical joints |
| Hot-Dip Galvanised | 0.18–0.25 | Apply molybdenum disulphide grease to control |
| PTFE/Xylan 1070 | 0.10–0.13 | Most consistent K-factor — preferred for critical |
| Electroless Nickel | 0.12–0.15 | Stable at high temperature |
LOKRON Technical Support
On request, LOKRON provides: target bolt tension calculations for your flange class and ASTM grade, recommended torque values for each coating type, and K-factor data sheets. This service has supported projects for NEWAY valve OEM, SUFA nuclear valve plants, and multiple EPC contractors in Europe and the Middle East.
Need this grade or specification?
LOKRON supplies PED-certified stud bolts and heavy hex nuts with full documentation.
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