As I understand PEEK can withstand higher temperature and stress as compared to PTFE.
I am mainly talking about valves here. I want to know the situations where PTFE can not be replaced by PEEK.
It may be any environment assuming PTFE can be used for that context.
The biggest issue I can see when switching from PTFE to PEEK is chemical compatibility. PTFE is basically inert, and has far better compatibility than PEEK with most fluids/gases.
When used as a seal material in valves there is a big difference in mechanical properties between PTFE and PEEK. Unfilled PTFE has virtually no mechanical strength and readily cold flows when subjected to any sustained pressure, while unfilled PEEK has fairly good mechanical strength. On the other hand, a PTFE valve seal would produce less friction, less wear, and have better conformability with the mating part than a PEEK seal would.
I suggest you check a compatibility chart for PEEK, pronto. PEEK and Teflon are very different in terms of chemical resistance, as well as physical properties.
And ask about fillers. Often with chemical attack it is the filler that is being attacked.
With PEEK you may be able to use unfilled, or PTFE filled versions even if you were using a filled PTFE, because it is so much stronger.
There are also many other related polyketone resins, PEK, PAEK, PEKK
I have seen PTFE and PEEK used mostly for Seat Insert Material in Ball Valves. Talking about chemicals, which are the chemicals where PTFE is more resistant than PEEK ?
PEEK as I know has higher wear resistance while PTFE is soft. Are there any fluid stream in Oil and Gas Production where PTFE is more suitable. Also I read in a forum that PEEK is more suitable in Upstream industries.
We like PEEK in gas services because it has lower permeability.
In liquid service you need to look at each chemical.
There is almost nothing that will attack PTFE, but for some high pressure services it isn't strong enough.
There are a number of environments that PEEK does not do well in.
Check the chemical comparability charts from the resin producers such as Greene Tweed, Solvay, or Victrex.
