we have a problem in our plant, with the valve seats of valves(safety valve), after a lot of checking seems that at least one of the causes is cryogenic thermal shock to the seat material.

kel-F, PTFE, or anything else just can?t keep it up, specially on the weekends the valve gets to ambient temperature or even more as it gets warm with the sun at maybe 50 C on the summer, and then the valve gets open all the way, in a couple of minutes (I have to measure this) it get down to -200 C (its used in both oxygen and nitrogen)

the original OEM part costs around 1500