Polytetrafluoroethylene, which is also known by abbreviation aficionados as PTFE, is a versatile gasket material. It’s a fluoroelastomer, a synthetic compound that’s available in many forms. On switching over to ePTFE (Expanded PTFE), the carbon-fluorine compound gains new mechanical properties. Classed as a popular sealing material because of a talent for resisting chemical attacks, ePTFE adds greater material conformability and creep resistance to an already impressive set of features.
What is ePTFE?
It’s a synthetic plastic that incorporates all of the features of PTFE while also adding a new set of mechanically improved attributes. That means expanded PTFE operates across a wide range of service temperatures and can shrug off caustic fluid attacks, as imposed by some of mankind’s harshest chemical mediums. On top of that, the plastic is more rubber-like, more conformable and seal-pliable. It goes without saying, but let’s say it anyway; these are the physical attributes that attract the gasketing industry. Resistant to high pressures, high and low temperatures, and material eroding chemicals, PTFE is a desirable gasket medium. Expanded PTFE, on the other hand, retains all of the above features, then it adds mechanical flexibility to an already attractive package.
Expanded PTFE: Uses and Applications
First and foremost, the conformable plastic finds itself die-cut into rings and seated against large flange faces. Heavy-duty bolts and nuts are tightened in special patterns so that installer-imposed compressive forces surround a seal and pipe cavity. The point being, ePTFE can endure the highest imaginable compressive energies, yet gaskets made from this flexible fluoroelastomer seal won’t crack under the pressure. Creep and blowout impervious, too, the gaskets can contain high-pressure fluid streams. Because of these features, expect to find ePTFE gaskets used in the kind of applications that employ continual thermal cycling. In oil refineries and chemical processing plants, in cryogenics facilities and heat exchanger usage areas, the seals cope with high-to-low temperature transients. Low-to-high thermal variances are similarly tolerated.
If that last sentence doesn’t quite make sense, imagine an active equipment line. Pressure vessels are storing a caustic medium in here. That substance is hot and being held at high pressure. Now, many gasket materials can tolerate one or two of those energetic threats. ePTFE can tolerate all of these threats. Even pressed down hard by two flange faces, the expanded PTFE holds firm. Better yet, though, if the system using the gaskets executes some kind of a phase change, one that changes the processing temperature or storage pressure, then the gaskets won’t suffer. Free of creep, strong and reliable, the fluoroelastomer withstands application and process transients.
Once upon a time, so the story goes, asbestos gaskets were commonly in-use because they provided exceptional thermal strength. The fibrous, silicate-based mineral obviously still exhibits superior heat-resistance fortitude, but asbestos is now recognized as an environmentally hazardous material, too. Known for some time now, the tiny fibres cause life-threatening lung diseases. No matter, a whole range of non-asbestos gasket materials are now available.
Compressed Non-Asbestos Gasket Solutions
It’s the compressed fibres that needed replacing during the whole asbestos removal crisis. And it was a crisis, with entire businesses popping up to withdraw the needle-like fibres from countless applications overnight. Sure, those fibres endangered gasket workers, but asbestos was also used as a structural insulant and fire-break, so older buildings used the fibres, too. Anyway, back to gasket applications, this fibre is undeniably dangerous, but it’s also inexpensive and rated to withstand enormous amounts of thermal energy. To replace the material, a whole new range of compressible synthetic fibres have evolved. They include Aramid, carbon fibre, and expanded graphite substitutes.
Equipped With Enhanced Friability Ratings
If a compressed fibreglass gasket is exposed to massive amounts of flange face stress, the synthetic fibre strands will crack and crumble. Under duress, perhaps because of a high bolt torque setting, the gasket fails because it disintegrates when compressed. Let’s leave fibreglass for those tasks that don’t need a lot of flange pressure, then. For high-pressure fluid loads, for liquids and gasses that are super-heated, a tougher synthetic fibre type is selected to overcome such sealing limitations. Designed to handle compressibility extremes and high-temperature fluid streams, the synthetics targeted here are purpose-designed to tolerate such energy extremes. Whether made out of Aramid or carbon, fibreglass or some brand-marketed seal variant, the fibres must be capable of being torque-tightened. Furthermore, the required level of compressibility cannot compromise the chosen fibre’s mechanical integrity.
Although the most physically essential part of a non-asbestos materials’ build, these fibres are only present in heat resistant gaskets in low percentages. Filling out the rest of the blend’s mix, an elastomeric compound provides additional seal resiliency. The non-asbestos gasket materials, be they made out of fibrous aramid or graphite, are blended with a binder, which adds more compressible strength to the product. Already capable of tolerating high temperatures and higher pressures, the right binder also incorporates a healthy measure of chemical resistance.
Again, due to their toxic properties, asbestos gaskets have fallen from grace, but that’s not a problem, not when there’s a whole range of compressible synthetic fibres and binders to fill the hole left by this formerly popular heatproof gasketing mineral.