Corrosion of Metal Components in Ultra-Low Sulfur Diesel USTs

The U.S. Environmental Protection Agency (EPA) released a study in 2016 that evaluated the potential corrosion factors for underground storage tanks (USTs) containing ultra-low sulfur diesel (ULSD) fuel. This study is important for understanding the increased number of corrosion problems in diesel tanks. This occurrence was magnified following the American Society for Testing and Materials (ASTM) reduction of sulfur content in diesel fuel to 15 ppm in response to the EPA’s emission mandates to control air pollution in 2006. Within a year of this reduction, several ULSD users reported clogged filters, broken seals, and other damage associated with USLD storage tanks and dispensing units to the Petroleum Equipment Institute (PEI). The first known cases of corrosion on internal metal components in the vapor space of diesel USTs was reported and published on the PEI’s website in 2007. Prior to 2007, corrosion within diesel USTs was generally perceived as occurring on the bottom of the tank.

The PEI revisited this incident in their First Quarter 2010 PEI Journal, which connected the possibility of ULSD to corrosion problems. The Second Quarter 2010 issue featured survey responses from participating associations as well as state and local UST offices concerning equipment issues encountered since the introduction of ULSD. The survey revealed 42% of responses reported an increase in equipment issues, which were spread across the United States and Canada.

The EPA’s investigation into this condition involved onsite inspections of 42 diverse operating UST systems across the United States. The UST systems included 24 fiberglass tanks and 18 steel tanks. The onsite inspections involved in-tank video cameras and photos along with collection of vapor, fuel, and aqueous-phase (water bottom) samples from each tank. Additionally, EPA personnel interviewed the UST owners concerning information on the storage history of the tank, operation conditions, and maintenance practices. Following the inspection, each UST was categorized into one of three groups based on the extent of corrosion: minimal, moderate, or severe. The resulting groups were then compared to determine trends based on the owner’s interview information and laboratory analytical results of the samples obtained.

The investigation results highlighted that moderate or severe corrosion on metal components in USTs storing diesel fuel is a very common occurrence (83%), and field observations identified corrosion in the upper vapor space of the UST system. This condition is a relatively new occurrence that can lead to malfunctioning overfill prevention, fuel level monitoring, or leak detection equipment. The study could not pinpoint the cause for this type of corrosion; however, water in the USTs and particulates in fuels appeared to be the factors closest to being predictive of corrosion.

Water can enter an UST system via damaged fill boxes, worn cap gaskets, loose fittings, poor maintenance of spill buckets, storm water accumulation within tank sumps, or condensation caused by fuel temperature changes or air entering through vents. Water entering your UST system can be prevented through the following practices:

At PSARA Technologies, Inc., we can assist UST owners/operators with evaluating corrosion on UST systems, assisting with upgrades to prevent water from entering tanks, determining if a tank has developed a leak, investigating potential fuel releases, and providing insight into liabilities associated with purchasing a service station.

A summary of the EPA’s report is available at: https://www.epa.gov/ust/alternative-fuels-and-underground-storage-tanks-usts#tab-5

The full EPA report can be found at: https://www.epa.gov/sites/production/files/2016-07/documents/diesel-corrosion-report_0.pdf

A link to the archived PEI Journal is available here: https://digital.peijournal.org/peijournal/20101Q?pg=52#pg52