It appears often in refinery and petrochemical specifications for critical service: Thermiculite® 835. What is it and which problem does it solve?
What it is
Thermiculite® is the registered trademark Flexitallic gives to its vermiculite based sealing materials. 835 is the grade of that family used as spiral wound gasket filler.
It exists because of the limit of graphite: in oxidising service at high temperature graphite loses mass, the gasket thins and bolt load drops. A vermiculite based filler does not behave that way and holds its thickness and load far longer.
Where it is specified
- Hot gas and flue gas ducts
- Catalytic units and regenerator surroundings
- Furnace, heater and boiler connections
- The hottest sections of steam lines
- Flanged joints with fire safety requirements
In these services the gasket is a safety item rather than a maintenance item, which is why specifications often name the brand directly.
Compared with graphite
| Criterion | Graphite filler | Vermiculite based filler |
|---|---|---|
| Oxidation | Mass loss above ~450 °C | No mass loss through oxidation |
| Upper temperature | ~550 °C in air | Around 1000 °C |
| Resilience | Higher | Lower |
| Cost | Low | Markedly higher |
| Typical use | General process | Critical, high temperature service |
The resilience difference matters: a vermiculite based filler tolerates flange distortion less well, so alignment and torque application need more care.
Supply and equivalents
Where a specification names the brand, there are two routes: supply the branded product, or submit a vermiculite based equivalent for approval with documented temperature limit, oxidation behaviour and fire test records where required. Approval can take weeks and belongs in the schedule.
Share your specification and service conditions and we will compare branded and equivalent options on price and lead time: enquiry form. Related: vermiculite filled spiral wound gaskets.
FAQ
What is Thermiculite® 835 made from?
It is vermiculite based; 835 is the grade used as spiral wound gasket filler.
Can it replace graphite everywhere?
It can, but it is rarely needed. It costs more and is less resilient, so graphite suits general process lines better.
What does substitution approval require?
Documented temperature limit, oxidation behaviour and, where required, fire test records.
Send us your material list; we reply with price and lead time the same day.
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