Discolored PTFE lining

[daviedalton]

Folks,

I've already tried this one elsewhere before I found the plastics forum, All comments appreciated...

We have what used to be virgin white PTFE lined piping, which would be exposed to almost everything you can think of , solvents, acids, bases, liquids and vapours at elevated temperatures. During a recent inspection, the internals of some lines were found to be a rust brown colour. The discolouration was distributed pretty evenly over the surface of the lining and could not be cleaned off.
One theory here is that the discolouration is a result of the PTFE being permeated by something. However after several hours surfing I failed to find anything on the internet that even suggested that PTFE could become brown. Is this a credible cause? Has anyone seen this before? I'm a little worried about the impact on the mechanical/chem resistance of my brown teflon....

PS this isn't a new issue for us, but we've never properly examined the cause behind the phenomenon..

cheers
dave

 

[patprimmer]

PTFE is very inert, but can be degraded under some severe conditions. I do not have data here at this time and I don't remember under what circumstances it does degrade.

PTFE mouldings are always at least a little porous as the melt viscosity is so high, that it is impossible to apply enough temperature and pressure to get enough flow to get complete homogeneous fusion of the moulding powder, hence it might trap some contaminants in the voids between the partly fused particles of PTFE powder

Regards

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