Researchers at the National Institute of Standards and Technology (NIST) have clarified that a study released in August should not be interpreted to suggest that ethanol blends can lead to rapid corrosion in gasoline storage tanks. The study was not intended to look for such a link, and those conclusions cannot be drawn from the study, said NIST metallurgist Jeff Sowards, one of the researchers on the study.
The study, officially published in the October issue of the “Corrosion Science” journal, looked at “rapid corrosion of components in some underground sumps,” not in the tanks themselves, Sowards said. He was quoted in an article published this week by the Steel Tank Institute (STI)/Steel Plate Fabricators Association (SFPA).
“The NIST research study focused only on the sump pump components of underground storage tanks, and the corrosion in storage tanks was not within the scope of the work,” Sowards said.
STI/SPFA itself added that “STI/SPFA maintains that this research should not be extrapolated to imply that microbial contamination in ethanol blend vehicle fuel storage tanks can be linked to corrosion other than in the sump head space.”
STI/SPFA continued: “Fiberglass reinforced plastic tanks, on the other hand, have developed cracks, blisters, and delamination, believed to be caused by storage of ethanol. … STI/SPFA has performed research to support that ethanol storage is not linked with steel tank failures. In fact, steel tanks have been conclusively shown to be compatible with all ethanol blends.”
The NIST research used “tightly controlled lab conditions” that “simulated sump environment” with water, ethanol and acid-producing microbes, particularly Acetobacter sp. The ethanol concentrations were 5%, according to Sowards.
Under those conditions, the microbes processed ethanol into acetic acid vapors that probably caused the corrosion. “In actual conditions, the ethanol concentration could vary, depending on fuel type and how well sealed the sump pump chamber is,” Sowards said, adding, “We do not know if … reports of corrosion inside underground storage tanks have any link to Acetobacter sp investigated in our study or any other cause (e.g. ethanol vapors).”
At the time the NIST study was released, OPIS reported accurately that it targeted corrosion of sump components. OPIS also reported that NIST researchers homed in on acetic acid as the probable cause of the problem.
However, ethanol trade groups sought clarification about the limits of study’s relevance to real-world conditions — the point affirmed by Sowards.
“The NIST researchers fail to provide relevance for the study, as the scenario could not occur in the marketplace today,” said Kristy Moore, vice president of technical services for the Renewable Fuels Association, at the time the study was published. “Additionally, they fail to acknowledge that ethanol has been successfully blended, distributed, stored and dispensed at retail fuel stations for decades with no equipment corrosion issues.”
