The term "carbon steel (PTFE) lining" often refers to a coating of polytetrafluoroethylene (PTFE) on the inside wall of carbon steel pipes. This lining combines the chemical inertness and non-viscosity of PTFE with the mechanical strength of carbon steel.
link:https://www.ttptfe.com/fluoroplastic-pipe/polytetrafluoroethylene-ptfe-lining/ptfe-lined-tubing.html