Biodiesel blends safe for steel tanks

By Jessica Ebert | May 14, 2008
A new study by the Steel Tank Institute confirmed that biodiesel is safe for use in underground steel storage tanks.

In the 12-week study carried out by an independent research lab, the corrosion of low-carbon steel, which is typically used for underground storage tanks, was so low that it couldn't be measured. The study results were presented at the 20th Annual National Tanks Conference and Expo in Atlanta in March.

The findings were surprising, said Lorri Grainawi, the institute's director of technical services. As the fuel samples aged, it was expected that acids would form and increase corrosion in the tested samples. However, the laboratory found no evidence of pits or corrosion, and periodic measurements with electrochemical impedance spectroscopy and mass loss studies showed an imperceptible corrosion rate. "The results were even better than we thought they would be," she said. "We designed this study to look at a range of conditions, including worst-case conditions, so it really covered everything we needed to consider. Unless something new comes up, I don't see the need for future studies. The results are very this will probably fix itself naturally with the other changes, but check it out just in case.

STI initiated the study for several reasons, Grainawi said. "Part of the reason for doing the study was just curiosity," she said. "We just wanted to make sure biodiesel was compatible with steel tanks. STI offers warranties on steel tanks, and that was part of the drive for the study. Also, Underwriters Laboratories was raising questions about biodiesel because all these tanks have UL listings. One of the arguments was that there is just no data on compatibility. Even though biodiesel has been produced and stored in steel tanks, there was just no test data."

Steel samples, which were immersed in blends of ultra-low sulfur diesel (ULSD) and biodiesel, were maintained at a temperature just under 110 degrees Fahrenheit. A small amount of rusting was noted on the samples. Slightly more rust was found on the samples submerged in ULSD than in B100. To more realistically reflect actual fuel storage conditions, water was added to half the samples.

The findings of the study, which was cosponsored by the National Oilheat Research Alliance and the National Biodiesel Board, were consistent with years of in-field use. "In nearly a decade of experience covering hundreds of millions of gallons of biodiesel being used, we have not experienced any problems with the compatibility of biodiesel blends in underground storage tanks," said Don Scott, a technical engineer with the NBB. "Biodiesel is nontoxic and biodegradable, and we are committed to promoting and encouraging environmentally safe storage and handling procedures."

Soy-based biodiesel, which was chosen for the experiment because it was the most commonly used in the United States, is also the most unsaturated common feedstock and represented a "worst-case scenario" for acid formation. A second study using biodiesel made from animal fats will be released later this spring. "Steel tanks have always been assumed to be compatible with any type of petroleum product," Grainawi said. "With the new alcohol fuels and regulations nowadays, it is something that has to be proven instead of just accepted. Regulators want to see some actual data."
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