The extremely stable structure of fluoropolymers results in their exhibiting outstanding corrosion resistance and thermal stability. These characteristics make them an excellent choice for use as linings in chemical process equipment. There are presently six fluoropolymers being used in equipment linings. Three of these materials are considered fully fluorinated fluoropolymers and three are considered partially fluorinated. The performance in service and the method of installation is different for each of these six materials. This paper details some of the performance characteristics and application procedures of these fluoropolymers when used as linings in chemical service.
The chemical resistance and thermal stability of fluoropolymers make them ideal for service as corrosion resistant linings in chemical process equipment, The same molecular structure that gives these materials outstanding corrosion resistance also results in fluoropolymers being unique to process and fabricate. Careful attention must be given to the installation of fluoropolymers to insure their overall performance in service is equal to their corrosion resistance.
There are currently six fluoropolymers commonly used as linings, These six materials are PTFE, FEP, PFA, ETFE, ECTFE, and PVDF. PTFE, FEP, and PFA are considered fully fluorinated and ETFE, ECTFE, and PVDF are considered partially fluorinated polymers. The fully fluorinated fluoropolymers exhibit resistance to a slightly broader range of chemicals than do the partially fluorinated fluoropolymers. All six of these fluoropolymers differ in physical properties. The chemistry of the fluoropolymers gives them their unique properties and will be briefly presented.
The difference in physical properties results in differing installation and fabrication requirements, PTFE, for example, is not melt flow processable. The rheological characteristics of PTFF result in the polymer decomposing before it reaches a flowable state. PTFE, therefore, is very limited in the methods of fabrication and is particularly limited in the methods which can be used to join or weld the material. The other five fluoropolymers are melt flow processable which results in there being a number of choices available for the method of installation and fabrication. The types of fluoropolymer linings which are used and the methods of their installation are presented.