Over the past 5 years, the RFA has been closely following the oil industry's investigation into a recent rash of corrosion incidents in storage and handling equipment for Ultra Low Sulfur Diesel (ULSD) use. Under normal, everyday storage and handling conditions, ethanol should never come into contact with diesel fuel; ethanol is a gasoline additive. However, a report released today by Battelle, sponsored by the American Petroleum Institute (API), claims the recent diesel fuel corrosion incidents stem from ethanol contamination.
Battelle's "Corrosion in Systems Storing and Dispersing Ultra Low Sulfur Diesel (ULSD), Hypotheses Investigation", September 2012, concludes that since 2007, the rash of ULSD corrosion incidents stems from acetic acid, otherwise known as vinegar, from review of the 6 sites inspected. The report states that "Acetobacter" (the bacteria known to produce vinegar) has the capacity to produce the type of corrosion witnessed at the half a dozen locations.
Starting in 2006, the U.S. Environmental Protection Agency (EPA) embarked on a self-described "ambitious strategy to reduce emissions from diesel powered vehicles." EPA mandated the reduction of sulfur content in diesel fuel, the main culprit for soot emissions leading to breathing difficulties, chest pain and coughing. For the majority of diesel fuel uses, EPA required the reduction of sulfur content from 500 parts per million (ppm) to a mere 15ppm by 2010. While the effort to improve air quality has positive health benefits, the impacts on fuel handling systems of removing such a large amount of sulfur from diesel fuel was unknown. Sulfur in motor fuels provided the fuel with a natural type of lubrication and helped prevent bacterial growth. The phase-in period for EPA's clean diesel program took place over a decade providing oil refiners with sufficient time to make the many changes to produce this low-sulfur diesel fuel.
Battelle's report attempts to draw meaningful conclusions from surprisingly few data points which leave fuel experts with many questions. Quite frankly, there are numerous plausible scenarios that can cause severe and rapid corrosion, including the monumental shift away from diesel fuel containing high levels of sulfur that took place in 2006. 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 are all equally important factors that should be investigated. The Battelle report acknowledges that "all of the sites inspected contained microbes," the root cause of the corrosion, which leaves one questioning the presence of other environmental influences, especially when the site selected as the baseline or control was also found to have the vinegar-producing bacteria present.
Another important investigative tool that can be used here is history and the timing of the corrosion events. Ethanol was introduced into the United States as a gasoline additive in 1978. However, it wasn't until 2007 that more than 50% of the gasoline across the US contained up to 10% ethanol. Only in 2011 did ethanol blended gasoline reach the saturation point of more than 90% of gasoline being blended with ethanol. However, for more than a decade significant volumes of ethanol blended gasoline were available in states like Illinois and Minnesota. If ethanol contamination were indeed the root cause of equipment corrosion that started appearing in 2007, then an epidemic of corrosion incidents would have plagued the storage and handling sectors since 2002 when ethanol replaced ground water contaminating MTBE as the oxygenate of choice by oil refiners. EPA phased in ULSD in 2006; never before seen severe and rapid corrosion incidents became a nationwide concern in 2006.
As the RFA was not included in the API's one-sided investigation into ULSD corrosion, there are some looming questions for the researchers:
- Illinois and Minnesota have had significant diesel usage and widespread availability of ethanol blended gasolines for more than a decade. According to this paper, this lethal combination should have produced catastrophic equipment damage in these states. Why did the study exclude Illinois and Minnesota?
- Traditional levels of sulfur concentration in diesel fuel are still allowed for non-road and marine usage. Were there any "severe and rapid" corrosion incidents observed in the higher level sulfur containing UST systems?
- Acetic acid, i.e. vinegar, was found to be ubiquitous in all of the UST sites inspected. But it appears that water was also found at each site. How much water contamination was seen in each of these sites?
- What effect does the additional refining process have on the overall composition of ultra-low sulfur diesel fuel? Where any common components of diesel fuel now eliminated or new components produced from the new refining process?
- Was there a commonality to any specific engineering type or materials of construction in the UST equipment that was susceptible to rapid corrosion?
- It appears there is an underlying concern with the general "housekeeping" with the findings of water contamination in both the underground storage tanks and the sump areas. Where there preventative maintenance programs or histories of regulatory concerns found at any of the sites?
