The increased prevalence of corrosion in the diesel infrastructure was first noticed in 2007, shortly after the introduction of ULSD (Ultra Low Sulfur Diesel) biodiesel blends. In 2016, the EPA published it's research results, which found 83% of storage tanks have moderate to severe corrosion. Corrosion has continued since 2016, do 100% of storage tanks now have moderate to severe corrosion?
The fuel is acidifying, and is corroding emergency backup generator injectors and storage tanks, increasing the risk of failure during a real emergency.
The main corrosion source is microbial growth in the fuel. Microbial growth produce both acids, acidifying the fuel, and biosurfactants, that create more micelles. Micelles form a bottom layer that enhances microbial growth.
This microbial growth has increased because water is bonding to surfactants such as biodiesel and ethanol, creating micelles, which form a layer on the tank bottom, providing a much larger volume that microbials can grow in. The biosurfactants then create additional micelles, greatly accelerating the corrosion process.
The cost of corrosion is immense. The lifecycle of tanks is reduced, normally tanks last for 30 to 40 years, now tanks have been replaced in as little as 10 years. The cost of removing and replacing these storage tanks is huge. The increased corrosion is affecting all parts of the diesel infrastructure, piping, fittings and seals, so environmental damage, and cleanup liability, is increasing.
Emergency generators are at risk, as acidified fuel corrodes the injectors. In addition, micelles are water droplets encased by surfactants, in this form traditional filters cannot contact the water, so micelles are bypassing these filters, entering the engine, and damaging injectors. A generator failure during an emergency will have a major impact on the public's health and safety, and on business operations.
Micelles facilitating corrosion crisis
There are two parts to the corrosion mechanism. In Part 1, free standing water moves permanently into the fuel column by combining with surfactants (biodiesel) forming micelles, and in Part 2, microbial growth follow the micelles into the fuel column; this greatly increases the microbial growth volume; more microbes, more acids, more corrosion.
The actual bonding mechanism of water to biodiesel is by a hydrogen bond. As seen in Figure 62 to the right, multiple surfactant molecules form a hydrogen bond with the water droplet, encapsulating the water forming a micelle. These micelles settle towards the tank bottom, forming a layer inches thick. Most fuel additives are surfactants, such as ethanol and biodiesel.
The micelle hides the water from traditional water tests such as water paste, and prevents the water from contacting traditional filter material, so are difficult to filter out.
Figure 62. Surfactants – a) schematic of surfactant molecule showing polar head and nonpolar tail; b) schematic of invert-emulsion micelle showing polar heads encapsulating water droplet and nonpolar tails extending into the medium (i.e., fuel); c) schematic of invert emulsion micelles dispersed in fuel; d) photo of 10 mL each fuel and water – left: before shaking; right: 24h after shaking (note stability of invert emulsion).
Figure 62 and notes from CRC Report No. DP-07-16-1 Identification of Potential Parameters Causing Corrosion of Metallic Components in Diesel Fuel Underground Storage Tanks, available at https://crcao.org/published-reports-full/
Being a polar molecule is why pure biodiesel can hold 15 to 25 times more water than pure diesel, and why micelles holding water are so difficult to remove with traditional filters. The micelle tails prevent the water from contacting traditional filter material.
Note: 100% pure ULSD and 100% pure gasoline are not polar, so do not bond to water. This is why, prior to the introduction of biofuels (biodiesel and ethanol), water was found mainly on the tank bottom. Microbial growth was mainly limited to the thin fuel/water interface.
Microbial growth follow the micelles into the fuel column to greatly increase their growth volume, and produce more acids.
Microbial growth permanently migrate into the micelle layer in the fuel column, as they now have the water they need to live there. This migration has greatly increased the microbial growth volume, resulting in more microbes, more acids, acidified fuel, and more corrosion. In addition, the microbes can create biofilms on surfaces that the diesel touches.
As well, microbes produce biosurfactants, which form additional micelles. It is the biosurfactants that are the main cause of micelle formation, and hence corrosion.
These factors have led to the corrosion crisis we now have.
Fortunately, the updated SAE J1488 filtration removes most micelles holding water.
SAE J1488 is the only recognized diesel industry filtration standard for biodiesel: “To determine the ability of a fuel/water separator to separate emulsified or finely dispersed water from fuels. This test method is applicable for biodiesel fuel.” This is the only test that specifically addresses biodiesel. SAE is the Society of Automotive Engineers.
Testing for water in micelles - ASTM D6304 Karl Fisher Titration
A key point is that in order to identify the presence of water in micelles, a Karl Fisher titration (ASTM D6304) must be used. Traditional test methods will not pick up the presence of water. For example, the visual “clear and bright” test will continue to be “clear and bright” no visible free water present. Water paste will not indicate water inside micelles.
Figure 62 from CRC Report No. DP-07-16-1
SAE J1488 is the only diesel industry filtration standard to specifically address biodiesel: “To determine the ability of a fuel/water separator to separate emulsified or finely dispersed water from fuels. This test method is applicable for biodiesel fuel.” SAE is the Society of Automotive Engineers.
The SAE J1488 test procedure can be purchased for $87 on the SAE site.
J1488 was updated in 2010 by SAE to account for the formation of micelles created by surfactants such as biodiesel.
The SAE J1488 test procedure tests a filters capability to break apart micelles to remove the water.
There are two phases of the J1488 test procedure;
1 - in the first phase 100% pure ULSD, is used. 2500 ppm emulsified water is added to a dry fuel sample. Since pure ULSD is not polar, micelles are not formed. All filters have as close to 100% efficiency in removing all the water.
2 - in the second phase, 2500 ppm water is again added to a simulated B20 biodiesel blend. The surfactant molecules encapsulate the water droplets, forming micelles as described above.
The traditional filters that rely on contacting water to remove it are inefficient at removing micelles, one vendor said they only had a 30% efficiency.
Filters need to be specifically designed to break apart micelles.
In order to reduce the bonded emulsified water to 200 ppm or below, a filters efficiency in breaking the hydrogen bonds to remove water will need to be 92%, (2500 * (1-.92)) = 200.
200 ppm of bonded water controls microbial growth of by limiting available water to the microbes; little water, little life, little MIC, corrosion controlled. As well, 200 ppm is the warranty level for emergency backup generators.
A new generation of filters have been developed since 2011 to remove the micelles as tested against SAE J1488.
The corrosion control mechanism is supported with field test results. Fuel samples from end user storage tanks using SAE J1488_201010 filtration consistently show water levels below 100 ppm.
Fuel samples that had been taken directly from the return lines, after filtration but before return to the tank, show as little as 14 ppm of water.
A key point is that in order to identify the presence of bonded water, a Karl Fisher titration (ASTM D6304) must be used. Other test methods will not pick up the presence of water in the micelle. For example, the visual “clear and bright” test will continue to be “clear and bright” with a slight haze, and no visible free water present. Water paste will not detect water in micelles.
An additional benefit of SAE J1488 filtration is that if properly installed, and run on an optimal schedule, the sludge and free water that normally deposits on the tank bottom is continually removed, such that storage tanks do not need to be cleaned again. The operational cost of keeping a tank clean and corrosion controlled is only the electricity used for the filtration system, and annual change out of filters.
Surfactants encapsulates water droplet. Water can't be detected or filtered. Note water not shown
The highest corrosion risk is for emergency backup generators, and their storage tanks. The fuel in emergency generator storage tanks is turned over very slowly; generators are typically tested on a monthly schedule for an hour or two. At this rate of fuel consumption, the fuel is effectively never replaced, just topped off a few times a year. While NFPA 110 recommends the complete replacement the fuel on a regular basis, in reality this is rarely followed. Water is continually absorbed and bonded to the ULSD biodiesel blend, and microbial growth continues unabated, acidifying the fuel, and corroding the tank and generator components.
The risk extends from the tank to the emergency backup generator itself, acidified fuel corrodes the micron size injector tips, greatly increasing the risk of generator failure during an emergency. In addition, excess water in the fuel flashes into steam at the injector tips, thereby increasing the damage to the injectors. During a real emergency, generators run 7/24, placing great stress on weakened injectors. A single injector failure will shut the generator down.
Biofilms provide a new threat to emergency generators. An engineer wrote this about the biofilm he found: “WOW. Never saw anything like this, check out the last picture. This was the consistency of boiled pig skin. It was lining the bottom of the tank. Super bugs.”
Biofilm can cause emergency generator failures by:
1 – corrosion of injectors and tanks components
2 – biofilm separates when fuel added, plug fuel pipes
3 – biofilm disintegrates, plugs filters
Most generator manufacturers have a 200 ppm warranty water limit, and have tightened up biodiesel warranty requirements. The amount of water in micelles that is delivered by diesel delivery trucks to emergency generator storage tanks can be well above 200 ppm, voiding the generator warranty from the first day of operations.
A key point is that in order to identify the presence of water in micelles, a Karl Fisher titration (ASTM D6304) must be used. Traditional test methods will not pick up the presence of bonded water. For example, the visual “clear and bright” test will continue to be “clear and bright” with substantial water in micelles, and no visible free water present. Water paste will not indicate water.
SAE J1488 is the only diesel filtration test to specifically address biodiesel blends, and tests the efficiency of filtration to remove all forms of water, including the biodiesel/water micelles. Removing all water controls corrosion
Atmospheric water (humidity) is absorbed into the biodiesel diesel blend, forming micelles, as the tank breaths. The addition of a dry gas into the Ullage and Interstitial space will blanket the diesel and keep the atmospheric moisture away from the tank walls, and diesel.
Identification of Potential Parameters Causing Corrosion of Metallic Components
in Diesel Fuel Underground Storage Tanks
Published 30 July 2021
From the report: “The results from this 12-week study confirmed that the presence of free-water was essential to corrosion.”
"Linking Fungal and Bacterial Proliferation to Microbiologically Influenced Corrosion in B20 Biodiesel Storage Tanks"
Published 25 February 2020
From the report: "Our in situ study showed greater corrosion near the bottom of each tank where the presence of water and a fuel-water interface was more likely. The interaction of fuel and water allows for enhanced microbial growth, and in turn, greater corrosion than water limited spaces within a fuel tank. "
EGSA Powerline Magazine:
"Corrosion Mechanism in Emergency Generators and Storage Tanks, and Corrosion Control"
The Electrical Generating Systems Association is the world’s largest organization exclusively dedicated to On-Site Power Generation, and includes most emergency generator manufacturers.
Mission Critical Magazine:
"Keep Generators and Storage Tanks Alive in the Wake of the Corrosion Crisis
Don’t discover the cost of corrosion the hard way"
SEE DOWNLOAD SECTION
New factors have caused the corrosion crisis, so new fuel tests are needed; three tests from a single diesel sample, and the total lab cost is under $100 for all three.
100 % biodiesel holds 15 to 25 times more water than that of pure 100% diesel. This is because both water and biodiesel molecules are polar (they have a positive and negative charge to the molecule), so the water molecules are attracted to, and bond quickly to, the biodiesel molecule. Pure diesel is not polar, so water does not bond to it. The actual bonding mechanism of water to biodiesel is by a hydrogen bond. While weaker than a covalent or ionic bond, it still attaches multiple biodiesel molecules to a water dtoplet, forming a micelle. This is why pure biodiesel can hold 15 to 25 times more water than pure diesel, and why bonded water is so difficult to remove.
Because the water is bonded to the biodiesel molecule, it does not show up in the “clear and bright” visual test, nor does the water precipitate out to the tank bottom until the biodiesel blend hits saturation, at which time there is a high ppm water bonded to biodiesel. The only way to detect the water is by using a Karl Fisher (KF) titration (ASTM D6304), which uses titration and an electric current through the diesel sample to provides the energy necessary to break the hydrogen bond and release the water. The water can now be detected and measured. The test procedure is common and inexpensive. To date this test has not been used much in the diesel storage industry, because before the use of biodiesel, water settled to the tank bottom. It is critical that a Karl Fisher test be used to detect water levels in stored biodiesel diesel.
End users can now get a fuel test kit specifically for microbiological contamination, which enables you to identify contamination in 15 minutes or less. Two companies that supply these kits are:
LuminUltra Technologies: https://www.luminultra.com/industry/petroleum-and-fuel/
Conidia Bioscience FuelStat https://conidia.com/diesel-fuel-contamination-test-kit/
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