Corrosion in Diesel Fuel Storage Tanks - The Results

Back in 2017, Bell Performance did a webinar on an important issue that we thought was important to share it with our blog readers: corrosion in diesel fuel storage tanks. Throughout four articles, we're sharing the content of that webinar here on the blog.

To set the table, the EPA collaborated with private industry groups to do the most extensive survey and study of the prevalence of storage tank corrosion that's been done up to this point. After the dust settled, what did the EPA find through its research survey and what were the takeaways they wanted the public to know?

You can read the first part of this series, Corrosion in Diesel Fuel Storage Tanks- The History of Corrosion.

You can read the second part of the series, Corrosion in Diesel Fuel Storage Tanks- The EPA’s Methodology.

Takeaway #1: Corrosion was a lot more common than they might have predicted

The main finding of their research was that tank corrosion was a lot more common than they might have predicted. 35 out of 42 tanks surveyed (83%) exhibited signs of moderate or severe corrosion.

what UST Elements were most susceptible?

Corrosion was observed on all types of metal components in the tank – turbine pump shafts (the most common place corrosion was observed), tank gauge probe shafts, flapper and ball valves, bungs, fuel suction tubes, and the tank inner walls. The corrosion was most often described as looking like layers of tubercles coating the metal surfaces of the equipment.

Reports ranged from just localized pockets of corrosion in small areas to uniform coverage of metal surface by corrosion in the vapor space

Takeaway #2: Most owners were not aware that corrosion could be affecting their tanks and Takeaway #3: Corrosion affected metal & fiberglass tanks equally

A second finding was that most owners were likely not aware that corrosion could be affecting their USTs. This comes from the fact that less than 25% of the owners reported having corrosion problems, but 83% of them ended up having moderate to severe corrosion damage.

A third finding was that corrosion affected both metal and fiberglass tanks equally. One might ask how fiberglass tanks could be affected at the same rates as metal tanks, but this is due to the metal components of the fiberglass tanks.

Takeaway #4: Exposed metal in the highest parts of the tanks exhibited the highest levels of corrosion damage

A fourth finding indicated the metal exposed in the vapor space (the highest part of the tank) had the most corrosion damage. The STP shaft was the component most commonly seen with the most advanced corrosion.  STPs are located in the vapor space, though it’s also exposed to fuel as it is dispensed.

In their report, the EPA noted that the appearance of the corrosion damage on STPs resembled layers of tubercles covering the metal surface.

Takeaway #5: Ethanol was present in 90% of fuel samples taken

Part of the testing protocols for the EPA's study was an analysis of samples of fuel, water bottoms, and vapor gas, each one taken from every tank in the study. With the liquid samples of fuel and water, the testing laboratories found widespread contamination by things that you wouldn’t expect to find in there.

They found ethanol was present in 90% of the fuel samples, which speaks to the strong possibility of switch-loading contamination referenced before.

Contaminants Identified in Samples

They also found ethanol presence in more than half of the water bottom samples pulled. Not all tanks had water bottoms. Only 11 of the 42 USTs had enough water bottoms for the technician to extract a sufficient sample for testing.

It’s notable that in most of the fuel samples, ethanol presence was detected (all but four). They also found gas contamination in every single sample, based on the identification of C4-C8 carbon chains.

Biodiesel content

What else did they find in the samples? We know that biodiesel blending is pretty much the defacto practice in the nation’s fuel supply. So we should expect biodiesel presence in most diesel fuel samples.

Biodiesel content was detected in 30 of 42 fuel samples (not surprising). In 20 of them (about half overall), the biodiesel % was between 1 – 5.3%. Only one sample had an abnormally high amount (11%).

So, what they find here is that by and large, the samples pulled from these storage tanks from across the country commonly had the presence of other things (ethanol, biodiesel) that would contribute to corrosion problems because of their affinity for microbes. Microbes love to feed on biofuels like ethanol and biodiesel.

Key Takeaways #6 and #7

The 6^th and 7^th findings were very interesting.

Sixth Finding – they tested each diesel fuel sample against the fuel specification and found that many of them did not all of the required quality standards in the spec. This means that if these are representative of UST systems across the country, then there are a lot of USTs storing fuel that is less clean and dry than the standards intend.

Seventh Finding – They also looked at the relationship between where fuel samples fell short of what they should have been. When they looked at how and where these fuel samples failed, and related it to the condition of the storage tanks the fuel was taken from, they found that the content of fuel particulate and water were the closest predictors of metal corrosion severity in that tank.

Microbially Induced Corrosion & Other Possible Causes in Tanks

Remember that one of the goals of the EPA in going through all of this was to gain better insight into narrowing down what exactly was causing this potentially serious problem. Their final result/takeaway concerned the phenomenon of Microbial Induced Corrosion. Based on their findings in the field, the EPA had some comments about how those interfaced with previous ideas on biofuels and MIC.

First, they didn’t feel the final results of the study proved or disproved the theory about microbes oxidizing biofuel components in diesel fuel. However, don’t mistake that for the EPA saying the theory is wrong. This was more about the level of evidence needed for an official governmental or scientific body to conclude “proves”. The EPA was pretty clear that there was strong evidence linking to that possibility. But the scope of the study would not “prove” the link. Instead, the study showed that the correlation was there and warranted more intensive study at a later date.

This link was supported by the properties of the water samples taken from the tanks. Remember that you need water presence for microbes to grow. They got sufficient water samples from 11 tanks. 5 of those 11 tanks were rated as severely corroded. Upon analysis, they found that all of the water phase samples had an acidic pH and all contained either ethanol combined with low MW organic acids – the kinds produced by microbes and associated with corrosion. Glycerin content was also detected in many tanks, which is another thing linked to microbial growth due to their affinity for using it as a food source.

So, the properties of the water samples from these tanks support the link between microbial activity and tank corrosion.

Overall, the EPA concluded that, while nothing is proveable, the evidence is strong that MIC is likely happening here, including a possible link to MIC related to biofuel components in diesel fuel.

Taking into account previous research, they hypothesized that biofuel components in diesel could be providing energy for microbial populations of bacteria like Acetobacter, which was the genus of bacteria most abundant in previous samples that underwent DNA sequencing.

But it should also be noted that numerous other types of bacteria could be consuming fuel components, in addition to other types of microbes themselves (fungi, eukaryotic).

The EPA also stated that they believed the number of tanks (42 systems), their diversity of type and operation and maintenance practices, and their nationwide locations, could lead them to declare the findings to be valuable in improving the understanding of the extent of the problem.

Now they are doing Phase 3, in conjunction with the Coordinating Research Council is currently in development and will seek to look more closely into the causes.

They may not have found the smoking gun in this study, but they’re a lot closer to the point than when they started. So, the study was a success – it got them a lot closer to their ultimate goals than they were before.

So, having discussed what the EPA was trying to do, how they did it, and the base conclusions the EPA pulled out of their study, we can now turn our attention to the best practice recommendations that they believe came out of the findings of their study. This is the meat of the matter for us. We know what the problem is, now we want to know the best ways to prevent those problems from biting us as tank owners.

The EPA gives six recommendations for tank owners and operators to combat and prevent this problem.

Learn More

Click here to read the first part of the webinar transcript: Corrosion in Diesel Fuel Storage Tanks- The History of Corrosion

Click here to read the second part of the webinar transcript: Corrosion in Diesel Fuel Storage Tanks- The EPA’s Methodology

Click here to read the fourth part of the webinar transcript: Corrosion in Diesel Fuel Storage Tanks- Recommendations for Tank Owners

You may want to check out these posts:

• "Wow" Facts on Contaminated Diesel Fuel. Be Prepared.
• Black Smoke From Diesel Storage Tanks? Try these suggestions
• Diesel Fuel Storage Problems and Solutions