OPINION: UST corrosion blame game continues

By Cassie Mullen, director of market development, Renewable Fuels Association | January 02, 2019

Let me make some bold predictions for the new year: for at least three months, I will accidentally write “2018” instead of “2019” when I date my checks; I will start and ultimately fail yet another diet; and, finally, biofuel 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. EPA held discussions with UST manufacturers, service and maintenance providers, retailers, fuel producers and others, and worked collaboratively to develop field-based research that would further the understanding of corrosion inside USTs storing diesel.

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.

Research into the issue is ongoing and is likely to continue for many years, but retailers should know that ethanol is not the culprit behind diesel UST corrosion. While there is no single reported solution to eliminate the issue, there are measures that sites can take to ensure they do not fall victim to the effects of corroded equipment. We know that bacteria and the “food” they feed on (i.e., fuel) are always present, but without water and oxygen, they cannot wreak the sort of havoc that is being experienced.

RFA suggests retailers consider the following suggestions from the National Association of Convenience Stores, and from EPA’s 2016 Report:

• Regularly monitor and remove any water present in the UST;
• Filter fuel for water and particulates before it is delivered into the UST or recirculate and filter water and particulates while it is stored Add nitrogen generating equipment to limit an oxygen rich atmosphere inside tanks;
• Use liquid corrosion inhibitor additives or other corrosion inhibitors, including filming amines; and
• Use biocides to kill or other fuel treatments to disrupt existing microbial colonies or prevent future MIC

RFA continues to work with experts in the field to ensure that we deliver the most up-to-date resources concerning existing fuel equipment, compatibility, and fuel specifications. If you have any questions or concerns, please reach out. We are here to help.

Please contact Cassie Mullen at 832-415-7882 or cmullen@ethanolrfa.org.