Consulting Services for Corrosion Control in Diesel Fuel and Emergency Generators
SAE J1488 is the recognized diesel industry filtration standard: “To determine the ability of a fuel/water separator to separate emulsified or finely dispersed water from fuels. This test method is applicable for biodiesel fuel.” SAE is the Society of Automotive Engineers.
J1488 was updated in 2010 by SAE to account for the increased water content of biodiesel blends, as indicated by the reduced interfacial tension (IFT) of ULSD biodiesel blends compared to the higher IFT of pure ULSD.
IFT is the ability of two fluids to repel each other. The high IFT in 100% pure ULSD means that water is easily repelled, and precipitates out to the tank bottom. Water does not bond to ULSD as ULSD is not polar.
Biodiesel is polar, as is water, so water bonds to the biodiesel molecule via a hydrogen bond, hence the lower IFT of biodiesel blends. With this hydrogen bond, the water is more difficult to remove using traditional filters. The added bonded water gives microbial growth an increased volume to reproduce in, therefore more acids, and the corrosion crisis.
The SAE J1488 test procedure tests a filters capability to break this hydrogen bond and remove the water.
There are two phases of the J1488 test procedure; in the first phase 100% pure ULSD, with its high IFT, is used. 2500 ppm emulsified water is added to a dry fuel sample. Since pure ULSD is not polar, the emulsified water is not attracted to, and is not bonded to, the ULSD. Any filter should have as close to 100% efficiency in removing all the water.
In the second phase, the IFT is lowered to 15-19 mN/m, simulating a B20 ULSD biodiesel blend, and again 2500 ppm emulsified water is added. Emulsified water is attracted to, and bonds to, biodiesel, so it is much harder to remove. This is when the hydrogen bonds come into play. In order to reduce the bonded emulsified water to 200 ppm or below, a filters efficiency in breaking the hydrogen bonds to remove water will need to be 92%, (2500 * (1-.92)) = 200.
200 ppm of bonded water controls microbial growth of by limiting available water to the microbes; little water, little life, little MIC, corrosion controlled. As well, 200 ppm is the warranty level for emergency backup generators.
A new generation of filters have been developed since 2011 to remove the bonded water by breaking the hydrogen bonds as tested against SAE J1488. A permanently mounted filtration system is added to the storage tank.
The corrosion control mechanism is supported with field test results. Fuel samples from end user storage tanks using SAE J1488_201010 filtration consistently show water levels below 100 ppm.
Fuel samples that had been taken directly from the return lines, after filtration but before return to the tank, show as little as 14 ppm of bonded water.
The only time the bonded water is above 100 ppm is typically after a fuel delivery, which speaks to the quality of fuel delivered, or a water leak into a tank; in that instance the leak was found and fixed. These very low levels of bonded water content (< 200 ppm) will deny microbes the water needed for growth; little water, little life, little MIC, corrosion controlled.
A key point is that in order to identify the presence of bonded water, a Karl Fisher titration (ASTM D6304) must be used. Other test methods will not pick up the presence of bonded water. For example, the visual “clear and bright” test will continue to be “clear and bright” with substantial bonded water, and no visible free water present.
An additional benefit of SAE J1488 filtration is that if properly installed, and run on an optimal schedule, the sludge and free water that normally deposits on the tank bottom is continually removed, such that storage tanks do not need to be cleaned again. The operational cost of keeping a tank clean is only the electricity used for the filtration system, and annual change out of filters.