From a metallic stress standpoint, PTFE effects should be mild, unless for some reason you have a very thick coat, which you can input as refractory to add weight. Otherwise, the pipe will by and large act like a steel pipe.

However, what we can't comment on will be the precise limitations to the flexure of the PTFE coating. Even the manufacturer would have problems with that, I'm sure.

For example, this is one manufacturer's design book.
http://www.corrosionfluid.com/assets/pdf...sign_manual.pdf