Technical Guideline

The Chemical Process Industries (CPI) face many challenges in the containment of highly corrosive products and intermediates, both in processing facilities and in the treatment of process wastes. Often the combination of temperatures and pressures severely limits the service life of conventional systems. Successful containment needs to be cost effective, safe and environmentally responsible.

These requirements create the need for more corrosion resistant equipment and piping suitable not only for aggressive individual chemicals, but also for multi-component mixtures, whose compositions may vary with time and over a wide range of pH. Historically, metals have been used to solve most corrosion problems, however, some current process conditions exceed the capabilities of even the most expensive and exotic metals.

As an alternative, fluoropolymers can provide successful containment facilities in many cases.Fluoropolymers are highly corrosion resistant to a wider range of chemicals at varying concentrations and pH’s.

Permeation is the transport of small molecules through the plastic liner. Permeation is a combination of absorption, solution, diffusion & desorption mechanisms. It is a function of several variables including the properties of the permeating species (i.e., molecular size, solubility parameters, concentration), properties of the plastic (i.e., crystallinity, density, thickness, thermal history), and operating parameters (i.e., temperature-pressure gradients and cycling). Permeation data published in most literature refers to thin coatings or films and should not be applied to plastic-lined products.

All products lined with fluoropolymers, such as PTFE, PFA, FEP, ETFE and ECTFE are subject to some permeation for certain fluids. Normally PTFE lined products in conjunction with the fluids having permeation in PTFE are substituted by PVDF to avoid permeation phenomenon.