Accelerated Corrosion in ULSD UST Systems Linked to Acetic Acid

September 17, 2012

A new study involving reports of accelerated corrosion in underground storage tank (UST) systems storing and dispensing ultra low sulfur diesel fuel (ULSD) has concluded that corrosion is likely due to the dispersal of acetic acid though the UST.

An independent study conducted for the Clean Diesel Fuel Alliance, found that acetic acid is likely produced by bacteria feeding on low levels of ethanol contamination. Dispersed into the humid vapor space by the higher vapor pressure and by disturbances during fuel deliveries, acetic acid is deposited throughout the UST system. This results in a cycle of wetting and drying of the equipment, which concentrates the acetic acid on metallic equipment causing severe and rapid corrosion.

The source of the low level ethanol contamination present in sampled ULSD tanks is not yet known. Contamination may be occurring in pipelines, terminal systems, cargo tank compartments or manifold vent systems. It is important to note that this phenomenon is still uncommon and primarily affects system components rather than the tank itself and has not caused any known releases. According to the report, It is too early to draw definitive conclusions on how ULSD tanks are being contaminated with ethanol or why accelerated corrosion occurs in a very small percentage of ULSD tanks while the majority of ULSD tanks remain largely unaffected.

The study, initiated two years ago after UST operators reported accelerated corrosion occurrences primarily in submersible turbine pumps, drop tubes, sensor probes and dispenser components, sampled six sites nationwide that reported the accelerated corrosion phenomenon in ULSD systems.

The Renewable Fuels Association (RFA) has questioned the findings of the study, arguing that numerous plausible scenarios could cause severe and rapid corrosion and should be investigated, including water contamination, humidity, ground water levels, incompatible UST equipment, nonfunctioning UST equipment, diesel fuel corrosivity, changes in chemical composition of diesel fuel, fuel additive over usage, diesel fuel additive under usage and microbial contamination.

The American Petroleum Institute (API) responded the researchers checked a number of hypotheses, weighed the data and came to a conclusion linking the problem to ethanol.

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This article originally ran in NATSO News Weekly (NNW), NATSO's member only weekly electronic newsletter. NNW is packed with the latest updates on government and business issues affecting the truckstop and travel plaza industry.

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