PTFE Teflon Gaskets are mostly suitable for pipes and flanges with highly corrosive and strong acid/alkalies. The inertness of PTFE is utilized to provide adequate sealing. Hard PTFE in Acid and Alkali is a poor substitute.
Due to Creep and Cold Flow, the Surface Stress on the PTFE changes over time and hence while sealing will initially work well, it will deteroriate over time and usually after a few months leakages will start. again The Property of Cold Flow and Creep in PTFE makes it extremely poor in respect to Sealing especially in a dangerous caustic environment