Graphite filled spiral wound gaskets cover most process piping. But once temperature rises and the atmosphere turns oxidising, graphite has a limit.
The limit of graphite
In contact with air, graphite begins to oxidise above roughly 450 °C. Oxidation means loss of mass: the filler thins, the gasket loses load and the joint eventually leaks. In a sealed, oxygen free environment graphite withstands far higher temperatures, so the atmosphere matters as much as the temperature.
The same applies where fire safety is required: the gasket is expected to keep its integrity during a fire.
What vermiculite offers
Vermiculite is a natural mineral and does not lose mass through oxidation. As a result:
- It holds thickness and load better at high temperature
- Its life extends in oxidising service
- Being non combustible, it suits joints with fire safety requirements
In exchange it is less resilient than graphite and tolerates flange distortion and slight misalignment less well. It is therefore used where genuinely needed rather than everywhere.
Comparison
| Criterion | Graphite | Vermiculite | Mica |
|---|---|---|---|
| Typical upper temperature | ~550 °C | ~1000 °C | ~1000 °C |
| Oxidising service | Limited | Good | Good |
| Resilience | High | Moderate | Moderate |
| Stripe colour code | Grey | – | Pink |
| Cost | Low | High | High |
Typical applications
Flue gas and exhaust ducts, catalytic cracking units, furnace and heater surroundings, hot gas lines, and flanged joints with a fire safety requirement.
When ordering
State service temperature, fluid and whether the atmosphere is oxidising. Winding material must also suit the temperature; high temperature grades such as 309 come into play here. If the specification names a brand, see vermiculite versus Thermiculite® for the substitution route.
Send your service data and we will define filler and winding together: enquiry form.
FAQ
To what temperature can graphite be used?
Much higher in oxygen free service; in contact with air, oxidation starts above roughly 450 °C.
Is vermiculite filler needed on every line?
No. Outside high temperature and oxidising service, graphite is both more resilient and more economical.
Does the winding material change too?
At higher temperatures grades such as 309 are preferred; filler and winding are chosen together.
Send us your material list; we reply with price and lead time the same day.
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