What Is Anti-Seize Compound?
Anti-seize compounds consist of metallic or non-metallic solid lubricant particles suspended in a grease or paste carrier. The solid particles (nickel, copper, molybdenum disulfide, or graphite) fill the microscopic surface irregularities between thread flanks, reducing the friction coefficient and preventing metal-to-metal contact that leads to galling and seizure.
Anti-Seize Types and Properties
| Type | Solid Lubricant | Max Temp | Nut Factor (K) | Best For |
|---|---|---|---|---|
| Nickel-based | Nickel flakes + graphite | 1,315 degC (2,400 degF) | 0.12-0.15 | Stainless steel bolts, high-temp, nuclear |
| Copper-based | Copper flakes + graphite | 980 degC (1,800 degF) | 0.13-0.16 | Carbon steel bolts, general industrial |
| Moly-based | MoS2 (molybdenum disulfide) | 450 degC (842 degF) | 0.10-0.13 | High-pressure bolting, subsea |
| Graphite-based | Graphite particles | 540 degC (1,000 degF) | 0.13-0.16 | Nuclear (no metallic contamination) |
| PTFE-based | PTFE particles | 260 degC (500 degF) | 0.12-0.14 | Chemical plants, food-grade |
| Zinc-based | Zinc flakes | 400 degC (752 degF) | 0.14-0.17 | Marine, galvanized fasteners |
Effect on Bolt Load
The nut factor (K) directly determines how much of the applied torque converts into actual bolt clamping force. The relationship is:
T = K x D x F
Where T = torque, D = bolt diameter, F = achieved bolt load.
| Condition | Typical K-Factor | Relative Bolt Load at Same Torque |
|---|---|---|
| Dry (unlubricated) | 0.20 | Baseline (100%) |
| Light oil | 0.17 | 118% |
| Copper anti-seize | 0.14 | 143% |
| Moly anti-seize | 0.11 | 182% |
| Nickel anti-seize | 0.13 | 154% |
The critical implication: if torque values are calculated for dry bolts (K=0.20) but the bolts are lubricated with moly anti-seize (K=0.11), applying the same torque will generate approximately 82% more bolt load than intended. This can exceed bolt yield strength, crack flanges, or over-compress gaskets.
Application Guidelines (ASME PCC-1)
ASME PCC-1 guidelines for anti-seize application on flanged joints:
| Guideline | Requirement |
|---|---|
| Where to apply | Threads, nut bearing face, and washer contact surfaces |
| Coverage | Complete, uniform coating; no dry spots or excess buildup |
| Torque adjustment | Mandatory; recalculate torque for the specific K-factor of the lubricant used |
| Documentation | Record lubricant type and K-factor on the joint record sheet |
| Mixing | Never mix different anti-seize types on the same joint |
| Shelf life | Follow manufacturer’s shelf life; expired compound may separate |
When NOT to Use Anti-Seize
| Situation | Reason |
|---|---|
| Bolt tensioning (hydraulic) | Tensioning measures bolt stretch directly; friction is irrelevant |
| Xylan/PTFE-coated bolts | Already lubricated; additional compound changes K unpredictably |
| Subsea bolts with factory coating | Manufacturer’s coating defines the K-factor |
| Torque spec says “dry” | Some project specs deliberately calculate for dry K-factor |
Galling Prevention
Galling is the primary reason anti-seize is mandatory on stainless steel A193 B8 and B8M stud bolts with A194 8 and 8M nuts. Austenitic stainless steel has a high friction coefficient and a tendency for adhesive wear (galling) when similar metals slide against each other under load. Without anti-seize, stainless bolts will gall and seize during tightening, making removal impossible without cutting the bolt.
Anti-seize selection directly affects gasket stress and sealing performance. Always match the torque value to the specific lubricant used, referencing the ASME bolt chart.
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