Wherever aggressive biodiesel and alcohol additives are utilised in motor fuels, it poses particular problems associated with unstable chemistry for any of the companies involved in production, blending, transportation and dispensing of such fuels. Relative to other fuel components, biodiesel is subject to degradation, particularly when combined with contamination as the increasingly aggressive fluid progresses through a production and distribution network.
Contaminated fuels can attack hydrocarbon rubbers such as nitrile, that are commonly used as the sealing medium for hoses, gaskets and O-rings used throughout the fuel handling processes. An additional problem of permeation is also encounted with nitrile rubbers where fuels incorporate ethanol. This can lead to the potential loss of expensive fuel and the emission of dangerous VOCs.
As biodiesel moves through the production/distribution network, it is increasingly contaminated with water and microbes, becoming more acidic in the process, and with detrimental effects on the nitrile rubber which can swell and soften. This results in diminishing seal strength and hardness, leading to eventual seal failures. For many years, however, Viton fluoroelastomer compounds from DuPont have successfully provided the ability to resist and withstand such attacks from a growing range of solvents and fuels.
Viton has also proved effective overseas, having been tested with US ethanol/gasoline blends, together with butanol which is also now being considered. Viton is also widely recognised for outstanding performance at elevated temperatures, as well as its suitability for conditions of -50°C to -65°C with certain biofuels when used for static sealing applications.
However, it is important to assure sealing products are ‘made with genuine Viton’, with the appropriate material and formulation fluoroelastomer supplied for each application. The typical resistance and low temperature properties for various types of Viton, featuring optional cure systems of Bisphenol or Peroxide, which are both illustrated in the table below. Except for the few instances where the Viton product is not recommended (indicated as NR), the resistance levels indicate either ‘excellent’ or’ very good’ results for the applications tested.
For more information, visit www.viton-orings.co.uk