Piping :
Flanged steel piping and a variety of fittings (T’s, elbows, reducers, spacers, etc.) are lined with PTFE tubes formed from granular or fine powder resins or melt-processible fluoropolymers. The ends of the tubes are flared over flanges by thermoforming so that fluids contact only PTFE surfaces when piping sections are joined, usually by bolting. The lining thickness is typically less than 6.4 mm (0.25 in.). FRP piping lined with fluoropolymer is manufactured by forming FRP over a fluoropolymer tube.
The resulting structure is called a dual laminate. Typically, the liner tube is a fluoropolymer such as PTFE, PFA, or fluorinated ethylene propylene (FEP). Glass fabric is embedded in the outer wall of the tube. This fabric bonds with the FRP structure so that the lining is held firmly in place. Lined FRP piping can be installed by welding of the linings and then covering the joints with additional FRP. This procedure is also used to form complex manifolds and transition pieces that are difficult or impossible to produce using lined steel. This installation method reduces the number of flanges in a piping system, which is desirable because flanges must be monitored for emissions and maintained by periodically checking the bolts for tightness. Forming lined piping in the desired configuration can reduce the number of flanges required for lined steel piping. This is accomplished by a proprietary process with pipe manufactured to withstand forming operations.
Vessels :
Steel vessels such as scrubbers and tanks are lined with fluoropolymer sheeting joined by welding. PTFE linings can be installed in this way, including those that have a glass fabric backing applied with proprietary technology. This backing allows adhesive bonding to the steel structure for better support of the lining, an important consideration if the process is operated at sub atmospheric pressures. Melt-processible fluoropolymers are used similarly to line vessels. They are easier to weld, and unlike PTFE, they can be readily thermoformed to fit vessel heads and provide connections for nozzles, or inlets and outlets.
Like piping, lined vessels can be constructed as dual laminates with FRP. In some applications, they are preferred to lined-steel vessels because the FRP vessels often have sufficient chemical resistance to prevent damage by spills, and they do not require periodic painting to prevent corrosion. Also, because of their lower weight they require less support thus installations cost less. Thermoplastic fluoropolymers can also be applied as coatings or linings by powder coating and rotational lining. Both processes provide relatively thick, void-free fluoropolymer layers compared to coatings obtained with PTFE dispersions. Fluoropolymers are applied to surfaces by powder-coating technique in much the same way as other polymers. The principal differences are higher temperatures required to melt the fluoropolymers, and more stringent surface preparation requirements.
In powder coating, powdered resin is applied to a surface using an electrostatic process and then heated in an oven so that the resin melts and forms a continuous layer. Additional layers are applied to reach the desired thickness. Rotational lining, or roto lining, is similar to rotational molding or casting, a process for forming shapes from polymers. The difference is that in roto lining, the product is a liner, while in rotational casting, the product is a formed part which must be removed from the mold. This process produces a seamless lining that can include multiple openings and complex shapes; thus, roto lining is well suited for CPI applications. it shows a comparison of rotational lining with alternative technologies. To line a vessel or a component, powdered resin is placed in the component’s cavity and all openings are covered. Then, it is rotated on two axes in an oven so that the resin melts and flows to cover all surfaces. The amount of resin consumed depends on the desired lining thickness. PFA, ethylene-tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), and ethylene chlorotrifluoroethylene (ECTFE) have been used with good success in roto lining. Manufacturers have report acceptable adhesion between the resin and the steel shell.