(Photo: A corroded flapper valve from a diesel tank, next to another flapper valve from the gasoline tank at the same site.)
By Brad Hoffman, Tanknology, Inc.
EPA began to phase-in Ultra-low Sulfur Diesel (ULSD) in 2006, with stringent regulations intended to virtually eliminate sulfur from diesel fuel and thereby reduce sulfur dioxide emissions. The EPA order was to reduce the sulfur content of all diesel fuel sold from a one-time high of as much as 5,000 ppm to a maximum of 15 ppm by 2014. Highway diesel was required to meet the standard by 2010.
Unfortunately, a problem quickly emerged. Water is very commonly found in diesel tank systems. The sulfur in diesel served as a critical biocide, which minimized microbial growth. So almost immediately, the tanks containing diesel fuel with virtually no sulfur started showing signs of aggressive microbial growth and corrosion. Diesel tanks and fueling systems developed corrosion that was growing so quickly, what would typically take many years to emerge was surfacing in a matter of months.
Last summer, the EPA released the first major study on the problem of this aggressive corrosion in ULSD tank and dispensing systems. Overall, the findings were staggering – with 83% of the tank systems in the study exhibiting moderate to severe corrosion.
But another finding was potentially the key to the rapidly-developing corrosion issue: The fuel in each of the tanks in the study was sampled and tested. In 90% of the tanks sampled, ethanol was present.
Ethanol is not blended with ULSD – at least not on purpose. It appears the ethanol that is so prevalent in diesel tanks is largely due to cross-contamination occurring when transport tankers switch from ethanol-blended gasoline in one run to ULSD in the next. It takes very little ethanol – trace levels – for certain bacteria to create the acidic acid that appears to be attacking many of these diesel fueling systems.
So what is there to do?
If you can see corrosion or microbial growth on your UST system components, or your dispenser filters are becoming clogged more frequently, it’s time to look further – and to assess the severity of the situation in your tank.
A corroded filter housing inside a diesel dispenser.
Sampling of the fuel is likely in order to determine what you have in the way of microbial growth in your system.
Then, most likely a thorough tank cleaning and filtration of the existing fuel is in order. Several companies provide a fuel filtration service. At Tanknology, we call ours FuelPure™ and here’s how we approach it:
The objective is the removal of particulates, water, sludge, algae and other microbial growth, as well as visibly dirty fuel, and return the tank system to a more optimum operating condition.
- Assessment: ATG inventory reports are run for each tank. Tanks are also manually sticked for product level and bottom water at multiple risers, verifying the low end of the tank. A bottom sample of fuel is collected at multiple risers for comparison in the filtration process.
- Application of Biocide: If microbial growth is present in the fuel or water bottom, a biocide treatment may be employed. A culture test may be utilized to confirm the type of growth. If it’s the first application in the tank, it may be ‘shocked’ with a high dose of biocide, per the manufacturer’s instructions, similar to how a swimming pool can be ‘shocked’ with chlorine to rid the pool of algae. Biocides may take up to 24 hours or more to have an impact on the microbes in the tank, though some claim to work within a few hours.
- Bottom Sweep: In some cases, a Bottom Sweep process may be employed once the biocide has killed the microbial growth in the tank. This sweep process is used to extract heavy debris and dirty product along the bottom of the tank.
- Fuel Filtration and Polishing Process: Fuel is drawn through an initial filtering process that removes the heavy tank bottom contaminants and water. The amount and types of contaminants are assessed and the contaminated fuel is passed through a series of several filters, removing suspended water and polishing the fuel through multiple stages, depending upon the level and density of the contaminants. Throughout the process, the intake hose is repositioned throughout the tank to ensure maximum fuel and tank cleanliness.
Incorporation of Remote Video: Tanknology also offers a unique tank cleaning service called TankClean™, which is a video-guided tank cleaning process. A proprietary camera is placed inside the tank and is remotely operated by a technician, providing a live view on a color monitor of the entire cleaning process. It provides a clear look at the condition inside the tank before, during and after the cleaning. Because the technician has visibility of the inside of the tank, the cleaning process can be precisely focused at the problem areas. When the cleaning is over, a digital file of the cleaning video is provided to the operator so they can see the before and after for themselves.
A preventive maintenance approach
Once your tank system and fuel has been cleaned and polished, it’s time to implement a strict comprehensive Preventive Maintenance (PM) approach to fuel management.
Rule Number One in dealing with fuel in the age of ethanol and ULSD is to MINIMIZE WATER. Water is the enemy of the fuel and tank system. Many of the problems discussed in this article can be avoided with an intensive focus on detecting and eliminating water from your UST system.
A comprehensive site inspection, fuel testing and treatment program should also be created in order to ensure that the fuel and tank system remains in optimum condition.
Many of our customers are leveraging the upcoming requirement for monthly site walkthroughs, by using a trained professional to also take multi-point fuel samples and periodically treat their tanks with biocide.
Given the composition of today’s fuels, the unfortunate reality is this: If your fuel and tank systems aren’t being closely monitored and carefully managed, severe microbial growth and corrosion is a matter of when, not if.
Brad Hoffman is Vice President of Engineering, Research & Development for Tanknology Inc. of Austin, TX, the largest UST compliance services company in the world. Brad is a 28-year industry veteran, formerly an engineer and program manager for Exxon. He serves on a variety of PEI and API technical committees. Brad can be reached via email at: bhoffman@tanknology.com.