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Corrosion Threat Seen to 500K Tanks

Thursday, August 7, 2014

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A half-million storage tanks installed below 156,000 gas stations in the United States could be harboring a "hidden hazard" in need of a pricey fix, federal scientists are warning.

A new study by the National Institute of Standards and Technology (NIST) "has demonstrated severe corrosion—rapidly eating through 1 millimeter of wall thickness per year—on steel alloy samples exposed to ethanol and acetic acid vapors."

EPA Sump Pump graphic
A NIST study found that corrosion may pose a hazard at underground gas storage tanks at filling stations. The study focused on sump pump components, especially the casings (labeled #3 in graphic), which are typically made of steel or cast iron.

In recent years, field inspectors in nine states have reported many rapidly corroding gas storage tank components such as sump pumps, NIST announced. The problems have been generally found in tanks that hold gasoline-ethanol blends.

Study: Vapors and Immersion

NIST followed up those field reports with a 30-day laboratory study of sump pump components, which are located above the tanks and directly below the access covers at gas stations.

The researchers developed new test methods and equipment to mimic the immersion, vapor and bacteria exposures of copper and steel alloy sump pumps.

The study "confirmed damage similar to that seen on sump pumps by field inspectors," NIST reported.

Steel exposed to vapors fared the worst, showing flaking iron oxide. Copper in both the liquid and vapor environments corroded more slowly.

Steel sample corrosion
Optical micrographs show severe corrosion on steel alloy samples exposed to ethanol and acetic acid vapors—typical conditions for USTs—after 355 hours, 643 hours, and 932 hours.

The immersed steel samples corroded most slowly—possibly because of a protective biofilm effect created by the bacteria, NIST said.

Tanks Vulnerable

The same rate of corrosion could afflict steel tanks and pipes exposed to the vapors, the researchers suggested.

“We know there are corrosion issues associated with the inside of some tanks," said NIST co-author Jeffrey Sowards. "We’re not sure, at this point, if that type of corrosion is caused by the bacteria."

Localized corrosion was also found on cold-worked copper, which is used in sump pump tubing and could leave the tubing vulnerable to stress-corrosion cracking.

Rapid corrosion could lead to failures, leaks and contamination of groundwater, NIST said.

The findings suggest that gas stations may need to replace their submersible pump casings sooner than expected, at a cost of $1,500 to $2,500 each, the team said.

Ethanol Challenges

Ethanol's corrosion implications are well documented.

Micrograph of crack

In a 2011 NIST study, ethanol-eating bacteria increased fatigue crack growth rates in steel 25-fold.

Much of the U.S. fuel infrastructure was designed for unblended gasoline, not the billions of gallons of corn-based additive now used annually.

NIST has reported on ethanol damage before. In 2011, NIST presented evidence that ethanol-loving bacteria "boosted fatigue crack growth rates by at least 25 times the levels occuring in air alone."

"We have shown that ethanol fuel can increase the rate of fatigue crack growth in pipelines," Sowards said at the time.

"Substantial increases in crack growth rates were caused by the microbes."

EPA Guidance

The U.S. Environmental Protection Agency also notes that biofuels "have significantly different characteristics than petroleum gasoline and diesel."

E85 STP Sump
Delaware DNREC (left); South Carolina DHEC

Technical/regulatory guidance released in 2011 by the Interstate Technology & Regulatory Council showed corrosion in two E85 STP sumps "likely caused by degradation products of ethanol vapors."

Ethanol in particular is "corrosive and highly water soluble," the EPA says. "As a result, special precautions must be taken in order to prevent corrosion of the [Underground Storage Tank] system and phase separation of fuel in the tank.

EPA warns UST owners and operators to "be aware of the technical and policy issues related to storing and dispensing biofuels, such as ethanol and biodiesel." The agency's UST office offers technical guidance on its Biofuels page.

In July 2013, NIST held a workshop on biocorrosion associated with alternative fuels. Those presentations and more information are available here.


Tagged categories: Corrosion; Environmental Protection Agency (EPA); NIST; Oil and Gas; Tanks

Comment from Tom Schwerdt, (8/7/2014, 8:36 AM)

Not surprising. As the article comments, ethanol is known to cause these issues - particularly in equipment designed for straight hydrocarbons.

Comment from Tony Rangus, (8/7/2014, 10:46 AM)

Makes one wonder what all those additional corrosion products are doing to the internal combustion engine that burns it?

Comment from M. Halliwell, (8/7/2014, 2:23 PM)

Tony, probably part of the reason so much of a modern engine is aluminum. :/ Tom, I found it interesting too....after years and years of just dealing with the natural processes getting at tanks and piping from the outside, the fuel makers change the mix and make it that much easier to kill a tank from the inside. It looks like I have job security for the rest of my career cleaning up these messes.

Comment from Frank Tomasi, (8/7/2014, 5:00 PM)

Two years ago the state of Florida banned the metal tanks causing all gas stations in the state to go to thick walled fiberglass tanks. The savings of 10% of fossil fuel is a bad trade off.

Comment from peter gibson, (8/7/2014, 5:17 PM)

Steel tank use is old technology. GFRP tanks outperform all metals for gasolene. Frank...savings of 10% ...what do you mean?

Comment from Tom Schwerdt, (8/8/2014, 8:19 AM)

M. Halliwell - good for you, bad for everyone else due to increased repair and remediation cost inflating the price of fuel. Fuel makers were under a continually-escalating Fed mandate to use more ethanol, which finally stopped ramping. Without mandate and a big fat subsidy, corn ethanol for fuel really doesn't make sense economically.

Comment from M. Halliwell, (8/11/2014, 12:24 PM)

Tom, I would love not to have the job security in this regards. Peter, I agree with you about the glass fibre long as they are installed correctly. We had a local station where the contractor didn't mix the adhesive correctly....during the first test, about 3/4 of the fittings and connections failed, blowing the fuel (limited quantity) out everywhere. It was a total mess :(

Comment from Tom Schwerdt, (8/12/2014, 8:35 AM)

M - no criticism of you was intended. Someone needs to do it :) peter - I suspect Frank is referring to the 10% ethanol in gasoline notionally "saving" that much gasoline, if you neglect lower efficiency and the petroleum products used in its production.

Comment from M. Halliwell, (8/12/2014, 10:56 AM)

Tom, no criticism taken. :) I've worked with a lot of "mom and pop" service stations in my career and it's heart-breaking to see the financial and emotional burden a leaking tank can we're getting a new mix of fuels that will potentially kill tanks faster and contribute to even more environmental messes and clean ups and more little small service stations being faced with huge remediations. It is job security for me, just not the way I'd rather have comes with a high price.

Comment from Tom Schwerdt, (8/13/2014, 8:39 AM)

...and last I heard, the recent highway bill took money out of the Leaking Underground Storage Trust fund and transferred it to the main Highway Fund....

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