Wednesday, May 1, 2013

Update on research targeting corrosion in ULSD systems

A significant topic in the petroleum storage and dispensing world in recent years has been the extreme rate of corrosion being experienced in some UST systems containing ultra-low sulfur diesel (ULSD). As early as 2008, this phenomenon was observed and by 2011 major industry organizations were in high gear in search of answers.

These organizations, which form the Clean Diesel Fuel Alliance (CDFA), awarded to the Battelle Memorial Institute with the support of Tanknology a research project intended to gain an understanding of what is causing the corrosion so that they might create a solution.

Battelle and Tanknology have now completed this initial project and the detailed findings are being reported in the current issue of the PEI Journal.

As a result of the sampling and analysis program in this study, the ultimate hypothesis was that the corrosion is likely due to the dispersal of acetic acid through the USTs.  This acid is likely produced by Acetobacter bacteria feeding on low levels of ethanol contamination. Dispersed into the humid vapor space and by disturbances during fuel deliveries, the acetic acid is deposited throughout the system. This results in a cycle of wetting and drying of the equipment, concentrating the acetic acid on the metal equipment and corroding it severely and rapidly. (The fill riser and STP photos to the right illustrate the severity of ULSD corrosion.)

But where is the ethanol contamination coming from? Initial study points to two possibilities: From switch loading or from a gasoline tank ventilation system that is manifolded with the diesel tank.

While this initial project provided an important step in possibly identifying the root cause of this rapid rate of corrosion, it did not provide enough certainty to justify changing the ULSD fuel distribution system.

The CDFA task force is now pursuing a next-level research project. In this advanced project, the hypothesis of the initial research will be further studied in order to prove or disprove it, as well as to provide a basis for alternative hypotheses if necessary and to identify the leading factors promoting the corrosive environment of ULSD systems.

According to Brad Hoffman, Tanknology’s lead scientist on the initial study, there is a clear sense of urgency in the work of the task force. “Corrosion at this rate of speed is very concerning,” Hoffman said. “So everyone is very anxious to understand why it’s happening and what needs to be done to stop it. At this point, we have what appear to be strong indications of what’s going on, but those need to be proven out so that corrective measures can be designed to mitigate this problem.”

So what can be done to minimize the potential for such corrosion in the meantime? According to Hoffman, “Until the absolute cause and a cure are identified, we recommend that operators keep their tank bottoms as absolutely free of water as possible. This is an important practice for any tank, but is particularly true of diesel tanks. Water is the enemy of fuel – especially diesel – in a UST.”

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