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Corrosion in Diesel Fuel Storage Tanks- The Results

Posted by: Erik Bjornstad

The first Bell Performance webinar of 2017 dealt with such an important issue that we thought it was important to share it with our blog readers: corrosion in diesel fuel storage tanks. Over the course of 4 articles, we will be sharing the content of that webinar here on the blog.

diesel fuel storage tanksYou can read the first part of this series, Corrosion in Diesel Fuel Storage Tanks- The History of Corrosion, here.

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

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

So, after the dust settled, what did the EPA find and what were the takeaways they wanted the public to know?

Takeaway #1: The main finding of their research was that corrosion was a lot more common than they might have predicted. 35/42 (83%) exhibited moderate or severe corrosion.

Susceptible UST Elements

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 describe 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 coming 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.

Third finding – 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

Fourth finding – the metal exposed in the vapor space (the highest part of the tank) had the most corrosion damage. The STP shaft was the component with the most advanced corrosion, and it’s located in the vapor space, though it’s also exposed to fuel as it is dispensed.

Note the photograph of one of the STP shafts in the study. Note the appearance of the corrosion damage – looking like layers of tubercles covering the metal surface.

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

Fifth finding – remember that part of the testing protocols was an analysis of all samples of fuel, water bottoms and vapor gas.  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 bottom. 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 upon biofuels like ethanol and biodiesel.

Findings & Key Takeaways #6 and #7

The 6th and 7th 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. Which 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.

And they also looked at the relationship between where fuel samples feel short.

Seventh Finding – 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 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

Now 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.

And their final result/takeaway concerned the phenomenon of Microbial Induced Corrosion. And 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 definitely 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 reach a conclusion of “proves”. The EPA was pretty clear that there was strong evidence linking to that possibility.  But the scope of the study wasn’t one that would “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 sample 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 + 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 the 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 there are numerous other types of bacteria that could be consuming fuel components, in addition to other types of microbes themselves (fungi, eukaryotic).

The EPA also stated that they believed the numbers of tank (42 systems), their diversity of type and operation and maintenance practices, and their nationwide locations, this 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 of 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:

Are You Fuel Ready? The Checklist

This post was published on March 21, 2017 and was updated on May 1, 2018.

Topics: Diesel, Fuel Storage, Fuel and Tank Services