FAME contamination of jet fuel: FAME is a surface active material and can adsorb onto the walls of tanks or pipelines and de-adsorb into subsequently carried products. This can be an issue where multi-product pipelines or storage tanks are utilised, or where ships carry jet fuel cargoes after carrying FAME/diesel blends.
The latest DEFSTAN 91-91 jet fuel specification states that jet fuel containing less than 5 parts per million (ppm) FAME can be considered acceptable for use, that is, can be considered as being free from any FAME. Full inclusion of this specification limit into the DEFSTAN 91-91 standard is pending on the development of a suitable test method to accurately identify FAME in jet fuel at this level. A test program conducted by the Joint Inspection Group (JIG) tested jet fuel dosed with various FAMEs up to 400 ppm and found no significant affect on specification test results, and the inclusion of the 5 ppm maximum limit into the DEFSTAN 91-91 standard has been granted on the basis that the aviation industry is working towards a 100 ppm maximum FAME content (DEFSTAN 91-91 Issue 6).
In May 2008 a number of jet fuel storage tanks at Kingsbury supply terminal and Birmingham Airport were quarantined after it was discovered that samples of the jet fuel in question contained up to 20 ppm of FAME. The cause of the contamination is thought to have been as a result of mixing of jet fuel with B5 diesel in the distillate manifold at Kingsbury terminal. As an indication of the very small quantities needed to cause such a contamination, the 5 ppm specification limit would be equivalent to just 1 litre of B5 diesel in 10,000 litres of jet fuel.
When vessels may potentially carry jet fuel cargoes following on from FAME or FAME/diesel blends, the JIG recommends that care must be taken with tank cleaning and flushing and draining common lines including sea or jetty loading lines. From experience, they suggest that switching from a B5 to jet fuel requires at least a hot water tank wash (but preferably also an intermediate FAME-free cargo) to remove FAME residue. Switching from neat FAME to jet fuel requires particular care and some advocate at least three intermediate (FAME free) cargoes plus the hot water wash before loading jet fuel (source: JIG Bulletin No. 21).
As 5 ppm is such a low level of contamination, there is the potential for erroneous results to be produced from inaccuracies in the test methods or incorrect sample handling. The DEFSTAN 91-91 standard suggests that the currently specified method of flushing sample
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containers three times for jet fuel samples may not be sufficient to remove traces of FAME, which may even be transferred from contaminated gloves. This could potentially lead to false positive detection of FAME in actually on-specification material, resulting in erroneous claims being made. It is therefore recommended that new sample containers and new gloves are used when sampling jet fuel cargos.
For products tankers carrying multiple products, the danger of inadvertently contaminating a cargo of jet fuel with traces of FAME is a very real risk, even if it does not initially appear that there is any potential for cross contamination to occur. For example, ultra-low sulphur diesel meeting the EN590 specification may appear in the shipping documents as ULSD, which would not immediately indicate that the product contained any FAME. However, the EN590 diesel specification allows up to 7% by volume FAME content. If the ship’s tanks and lines are not completely stripped of all the ULSD prior to loading a cargo of jet fuel, the quantity of ULSD containing 7% FAME needed to render the jet fuel cargo off-specification would be very small.
Solvent behaviour: An interesting property of FAME is its ability to act as a solvent, taking up any organic residue, dirt or scale that may have accumulated on surfaces of tanks or pipelines. This can have the effect of cleaning out the dirty storage or pumping systems but contaminating the FAME itself, and may lead to subsequent fouling of filters or pump blockages.
As an indication of its solvent strength, researchers from Iowa State University are investigating how the solvent properties of FAME can benefit military applications, by looking into whether or not certain varieties of waste generated in-situ in battlefield
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