Fluroopolymer linings in railcars can be used to ransport high purity and corrosive chemicals. The fluoropolymer materials offer outstanding chemical resistance and excellent barrier properties. This paper presents information on the installation of fluoropolymer lining system, material information on the installation of a fluoropolymer lining system, material selection, testing, and inspection of the installed system in a railcar lining.
Material Selection
Lining Installation
Inspection Procedures
Safe, high-purity transportation of chemicals from the chemical manufacturer to the end user in a semi-conductor processing facility can be accomplished through the use of a fluoropolymer lined railcar. There are three essential points to be addressed when considering the fluoropolymer lining of a railcar.
All system components associated with the railcar that come in contact with the chemicals being handled such as dip pipes, manway covers, internal supports, valves, and all internal surfaces of the railcar must he completely compatible with the chemicals being transported. Chemical attack or degradation of these components will cause unacceptable contamination as well as the potential for failure of the railcar lining system. For this reason, the fluoropolymer family of engineering plastics have become a typical material of construction for internal lining systems and component protection in semiconductor equipment.
There are a variety of fluoropolymers currently being used as linings, coatings, and extruded component parts. They are often recognized more by their initials than by their generic names, for example; PVDF, E-CTFE, E-TFE, FEP, PFA, and PTFE (see figure 1 for physical properties).
Polyvinylidene fluoride (PVDF) is available as melt-processable pellets and powders. Because of its excellent resistance to aging, chemical attack and high mechanical properties, PVDF has found numerous applications in fluoropolymer sheet lined transportation equipment.
Ethylene Chlorotrifluroethylene (E-CTFE) and Ethylene Tetrafluoroethylene (ETFE) are also applied as sheet lining materials. The combination of chemical inertness, low vapor permeability and suitability for extremely high purity applications have increased the usage of these fluoropolymer materials in lined equipment.
Polytetrafluoroethylene (PTFE) is one of the first fluoropolymers dating back to its discovery more than 50 years ago. PTFE is restricted somewhat by its processing methods. Some 30 years ago fluorinated Ethylene Propylene (FEP) copolymers were developed and provided more conventional melt-flow processability than PTFE, Pertluoroalkoxy (PFA) developed in the early 1970’s also allowed for melt-flow processing without substantial property differences from PTFE. While the properties of PTFE, FEP, and PFA are all very similar at room temperature, their primary applications have been in combinations of hostile chemicals at high temperatures and this coupled with economic considerations has limited their use as a railcar lining material.
There are a wide variety of chemicals being used in the semi-conductor industry. An uninterrupted supply of these high purity chemicals from the manufacturer to the end users process tools is necessary.
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Many material selection decisions on which lining system is suitable for a particular chemical are made based upon corrosion resistance data supplied by the fluoropolymer resin material manufacturer.
