Diesel Fuel Storage Tank Study Identifies 11 Corrosion Factors

The report found no significant link between corrosion and biodiesel or corrosion and sulfur content.

August 06, 2021

Diesel Tank

ALEXANDRIA, Va.—The Coordinating Research Council (CRC) this week released a long-awaited report on the factors that might contribute to accelerated corrosion in diesel fuel underground storage tanks, confirming that the presence of free water is essential to corrosion.

The project, “Identification of Potential Parameters Causing Corrosion of Metallic Components in Diesel Fuel Underground Storage Tanks,” was commissioned to determine how a variety of select factors affected ferrous metal corrosion, either directly or through interactions among two or more factors. The results will help direct attention and further study to help prevent corrosion in underground storage tanks. The study was sponsored in part by NACS.

“For more than a decade, we have been receiving reports of accelerated corrosion in underground storage tanks containing diesel fuel,” said Fuels Institute Executive Director John Eichberger. “Several studies have been conducted with limited results. This CRC study represents the latest and most scientific laboratory examination of potential factors to determine what might be causing this corrosion, which we hope will lead to strategies to help prevent it from occurring.”

The CRC’s Fuel Corrosivity Panel (FCP) identified 11 factors likely to be responsible for the increased incidence of corrosion: diesel sulfur levels, biodiesel, lubricity additives, conductivity additives, cold flow improvers, corrosion inhibitors, fiber reinforced polymer material, free water, microbial population, glycerin and ethanol.

The panel also determined that lab-scale testing is the most appropriate means of assessing how these factors contributed to fuel corrosivity. The final design included 128 test jars, containing metal strips representing steel tank bodies, used to assess the impact of the controlled variables on corrosivity. Results were observed or measured during a 12-week period.

In addition to the free-water finding, the report found no significant association between corrosion and biodiesel nor corrosion and sulfur content. It also reached no conclusions regarding corrosion associated with specific types of microbes or the acids excreted by those microbes. Laboratory observations did support the hypothesis that acetic acid formation is linked to microbial action on ethanol contamination in the diesel fuel underground storage tank, but direct correlations between acetic and corrosion were inconclusive.

The report noted that future studies should focus on the relationships between water and the following variables: microbial contamination, FAME (fatty acid methyl ester, or biodiesel), ethanol and sulfur concentration, because significantly increasing and decreasing rates of corrosion were observed in the varying medias tested. The report also suggests that future studies should include volatile organic acid accumulation in the vapor-phase (tank headspace).

“The conclusion that mild steel corrosion was unequivocally associated with the presence of free water and that water was the only independent variable that correlated positively with all of the independent variables highlights the importance of tank owners’ conducting effective maintenance of their systems to prevent water intrusion and accumulation,” Eichberger said. “There is nothing more important to mitigating the risk of corrosion than this important step.”

To assist tank owners in maintaining their systems, the Fuels Institute’s Diesel Fuel Quality Council earlier this year published the report, “Diesel Storage Tanks: Industry Practices to Minimize Degradation and Improve Fuel Quality.” In addition, the results of the Council’s project testing diesel fuel properties from 190 retail nozzles and 135 diesel storage tanks will be published later this year. Combined, the results of the CRC report and the upcoming Fuels Institute study should provide additional insights to facilitate development of effective solutions to mitigate corrosion in diesel fuel storage tanks.