Corrosion resistance in biofuels and biofuel blends
The corrosion resistance of storage tanks, process pipework, and pipelines is an important material requirement for the storage and transportation of fuels. The materials along which fuels are conveyed, especially, can suffer considerable damage due to stress corrosion cracking (SCC) and microbially-induced corrosion (MIC). Whereas the corrosion behavior occurring in relation to fossil fuels has been adequately studied and documented – like, for example, in ASTM D 7548 – systematic studies of biofuel corrosion are still lacking to a large extent. What is clear, is that, owing to the various chemical and physical properties, fossil fuels and biofuels differently influence the corrosion behavior at the interface between the material and fuel. Corrosion behavior is generally expressed in terms of the corrosion potential as a characteristic electrochemical value.
Biodiesel shows a high corrosion potential
Biodiesel has a higher electrical conductivity and is more hygroscopic than conventional diesel fuel. This means that, when stored for a long time, it absorbs more water, which in turn leads to hydrolysis of the ester bonds and thus to the formation of free fatty acids. The pH value falls and the microbiological activity responsible for degradation increases. With the biotic degradation reactions, the properties of the biodiesel also change; in particular, the corrosion potential at the material-fuel interface increases.
