Chemical Resistance Of Composites

Composites do not corrode because they are non-conductive. Therefore, an electrochemical reaction does not take place. (An exception to this may be when electrically conductive long carbon fibers are used in the wrapping of a pressure vessel or a pump housing.) Their lack of resistance to different chemical fluids can degrade composite materials. This degrading can be in the resin, the reinforcing fiber, or in the coupling agent between the resin and fiber. If a composite material is going to be degraded, it will usually be immediate. Fluid temperature and concentrations are vital when selecting the appropriate composite material. With some composites, such as nylon, the pH can be a factor when selecting the best composite material for the application.

As an initial test, a sample coupon of the composite can be immersed in the process liquid and the results noted. A more definitive method is to review the composite manufacturer's informational database on chemical resistance. Many composite manufacturers have run extensive chemical resistance studies of their materials in a variety of liquids at set temperatures over time. The composite's physical properties are measured before and after the test period and the percentage deterioration versus time is documented in the manufacturer's literature.

The Hydraulic Institute, discussed later, has a polymer material selection guide that recommends specific composites for various liquids.

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