OPINION: UST Corrosion Blame Game Continues

by Cassie Mullen (Renewable Fuels Association/Ethanol Producer Magazine) ... (B)iofuel opponents will continue to blindly blame ethanol for corrosion in underground storage tanks (USTs). However, ethanol is not the culprit, and retailers need to know the facts to help fight back against misinformation.

Beginning around 2007, UST owners reported new incidents of severe and rapid corrosion of internal metal components in their diesel fuel tanks. These reports typically described severe corrosion of equipment in upper portions of UST systems in the areas generally not submerged in fuel. Prior to 2007, a corrosion risk in diesel fuel tanks was considered minor. If corrosion in a diesel tank occurred at all, it often appeared in the wetted, or lower, portions of the tank. Because of the sudden change, many started searching for the culprit and pointing fingers. Ethanol quickly became the number one scapegoat due to its strong emergence across the country around that time.

The ethanol industry forcefully responded to reports that it was to blame. It just didn’t add up. Why would there be ethanol in the diesel fuel being stored in these USTs? Where would it have come from? Why were we not seeing corrosion to the same degree in tanks that had been storing ethanol-blended gasoline for many years? If this was really the cause, why did it not start decades earlier in the Midwest when ethanol was first introduced in the region? In an attempt to get to the bottom of the issue, EPA began researching the problem to understand the seriousness and extent of the metal corrosion issue.

While initial research was almost exclusively focused on diesel USTs, EPA found there had also been an increase in corrosion in USTs storing fuels other than diesel, and corrosion has been seen at the refinery level (i.e., in tanks that have never held ethanol). EPA has now initiated additional research to pinpoint the causes of the problem, but if corrosion is occurring in refinery storage tanks that have never held ethanol, how could ethanol be the problem?

The corrosion mystery has not yet been solved, but there are a few theories floating around. For instance, a 2016 EPA report concludes that, "It does appear that microbially-induced contamination (MIC) is likely occurring in USTs storing diesel. Taking action to limit the environmental conditions necessary for microbial growth is recommended by multiple industry groups and anecdotally appears to be successful in minimizing the chances of severe corrosion in USTs."

Beginning in 2006, EPA began to phase-in more stringent regulations to lower the amount of sulfur in diesel fuel. This fuel, known as ultra-low sulfur diesel (ULSD), was fully phased in for on-road diesel fuel by 2010. Many experts believe the transition to ULSD removed the very element—sulfur—from diesel fuel that helped keep microbially-induced contamination in check. It turns out that while sulfur is no friend to air quality, it helped stave off the microbial activity that can lead to corrosion in diesel tanks.