Corrosion Mechanism and SAE J1488 MICELLE Filtration
The Corrosion Crisis
We Thought the Main Cause of Diesel Corrosion We See Today was Microbial Influenced Corrosion (MIC).
We Were Wrong
MIC has affected stored diesel since diesel was invented over a century ago. Microbes need food and water for growth; their food is the diesel itself and water condenses from the atmosphere, then sinks to the diesel storage tank bottom. Microbial growth is at the diesel/water interface, a very thin layer. This is where in microbes produce acids. Corrosion was relatively minor, due to this extremely thin diesel/water interface.
What factor has changed to create the corrosion crisis that's being reported now?
The 2016 EPA report: “We observed 83 percent of the inspected tanks had moderate or severe metal corrosion. Prior to our research inspections, less than 25 percent of owners reported knowledge of corrosion in their UST systems ..." EPA Report July 20th 2016 “Investigation Of Corrosion-Influencing Factors In Underground Storage Tanks With Diesel Service”
Diesel was always the plentiful food, so no change here. What has increased the water content in diesel storage tanks?
ULSD (Ultra Low Sulfur Diesel) was introduced in the US in 2006. There were soon reports of catastrophic engine failures. The process of removing the sulfur also removed the lubrication inherent in high sulfur diesel.
In order to prevent these engine failures, each refinery added a lubricant to their ULSD. Surfactants are very good lubricants for diesel. Initially there was no standardization on the lubricant used, each refinery added their preferred lubricant. Adding biodiesel (FAME) restored lubricity very effectively—often better than conventional lubricity additives. There is now 5% biodiesel added to ULSD (B5), and higher concentrations are available such as B20 and B50.
It was after the addition of surfactants as lubricants in 2016/2017 that enhanced corrosion was noticed. So how would surfactants increase water in a diesel storage tank?
Water is a polar molecule, it has a slight charge that attracts other water molecules, this can be seen in the surface tension on a pond, and in water droplets forming on the outside of cold drinks on hot humid days.
Surfactants are also polar, they are attracted to water, and then encapsulate water droplets (see diagram) forming inverse micelles. These micelles are heavier than diesel, so they settle to the bottom, and stack on top of one another, forming a thick layer, up to 6 inches thick. These 6 inches of micelle volume is magnitudes greater than the thin water/diesel interface previously found in high sulfer diesel. This thick micelle layer provides an enhanced growth medium for microbes. Microbes in this thick micelle layer produce magnitudes of more acids.
This inverse micelle formation process is unknown to most people, but one major standards organization recognized this issue and has engineered a solution to remove the water in micelles. The SAE (Society of Automotive Engineers) sets filtration standards, and has a standard SAE J1488 that specifically tests the efficiency in the removal of water in inverse micelles. In the test procedure 2400 ppm water is mixed into ULSD, along with enough surfactant to emulate a B20 fuel mix.
Filters tested by SAE have shown 100% removal of water. Note SAE J1488 was updated in 2024.
In summary, control the water in stored diesel, and you control microbial growth, hence corrosion.
If you have a corrosion issue, or want to prevent a corrosion issue, filter your stored diesel with filters tested by the SAE J1488 test procedure with a 100% efficiency in removing water.
Surfactant molecules encapsulate a water droplet. Note water droplet not shown in middle
The Corrosion Mechanism
The Corrosion Mechanism
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.
Part 1:
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.
https://biodieseleducation.org/Literature/Journal/2007_He_Moisture_absorption_.pdf
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.
Part 2:
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 Filtration for Corrosion Control in Diesel
Additional Information
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.
www.sae.org/standards/content/j1488_201010/
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
Emergency Generator Risk
Single Point of Failure in Emergency Generators
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.
Corrosion Control
Corrosion Control Diesel - SAE J1488 Filtration
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
Water Absorbtion Control
Nitrogen Gas Blanketing System
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.
LATEST INDUSTRY CORROSION Articles
Additional Information
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.”
https://crcao.org/published-reports-full/
"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. "
https://www.frontiersin.org/articles/10.3389/fmicb.2020.00167/full
EGSA Powerline Magazine:
"Corrosion Mechanism in Emergency Generators and Storage Tanks, and Corrosion Control"
http://www.egsa.org/Publications/PowerlineMagazine.aspx
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"
www.missioncriticalmagazine.com
SEE DOWNLOAD SECTION
HOW CORROSIVE IS YOUR DIESEL? 3 Tests to find out
Additional Information
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.
- TAN (Total Acid Number) ASTM D664 - indicates how acidic your diesel is. Maximum .08 mg KOH/g
- ASTM D6304 (Karl Fisher titration), registers *all* water, including the new water format, bonded (entrained) to biodiesel molecules. This water enables microbial growth in the diesel column. Less than 200 ppm water controls MIC
- ISO 4406 standard particulate test - general indicator of diesel quality, plus can also indicated the amount of microbial growth. Maximum 18/16/13
Why a Karl Fisher test is needed
Additional Information
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 User Microbial Testing, Simple and Inexpensive
Additional Information
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/
