flexible graphite gasket

A spiral wound gasket is the most common metallic gasket used in industrial plants.A
properly selected and installed spiral wound gasket can withstand high temperatures and 
pressures,preventing leaks throughout their intended lifespan.
A spiral wound gasket condists of three elemnets:
Outer ring,made of carbon steel,this outer ring is sometims called the centering ring or
guide ring,It's used to center the gasket when you insert it into a bolted flange joint.
inner ring,The inner ring is pivotal for the gasket because it prevents windings from buckling
inside the pipe,when a gasket buckles,parts of it get sucked into the pipe.From there,pieces of
the gasket will typically flow through the pipeline until they get caught on somthing.
Often,they'll get wrapped around rotating equipment like a pump .Inner rings help you avoid this problem.

Sealing element.As you might guess from the name ,the sealing element creates the seal that prevents leaks.A sealing element encompasses both windings and filler material .Most spiral wound gaskets in oil and gas refineries will use a flexible graphite filler material rated for high temperatures. A flexible graphite filler also allows the gasket to be more tolerant of flange distortion and joint misalignment. Polytetrafluoroethylene （PTFE) is another common filler material . PTFE is not rated for high-temperature applications.