Study Suggests Severe Corrosion of Some Storage Tank Components

A recent National Institute of Standards and Technology (NIST) laboratory study suggests that “many” of the sump pumps for underground storage tanks at gas stations could corrode more rapidly than expected.

NIST, a non-regulatory federal agency within the U.S. Department of Commerce, duplicated conditions similar to those found around the sump pump for tank systems to determine the potential corrosion rate.

The study “demonstrated severe corrosion rapidly eating through 1 millimeter of wall thickness per year on steel alloy samples exposed to ethanol and acetic acid vapors,” NIST said. “Gas stations may need to replace submersible pump casings, typically made of steel or cast iron, sooner than expected.”

The laboratory study was prompted by recent reports from field inspectors in nine states suggesting there were “many” rapidly corroding gasoline storage tank components such as sump pumps, NIST said in an announcement. The incidents are “generally” linked to the use of gasoline-ethanol blends and the presence of bacteria, Acetobacter aceti, which convert ethanol to acetic acid, a component of vinegar, the agency said.

The NIST study “confirmed” the field inspectors’ reports of damage to sump pumps, NIST said.

A request for comment from ethanol supporter the Renewable Fuels Association was not answered by presstime.

Researchers developed new test methods and equipment to study copper and steel alloy samples either immersed in ethanol-water solutions inoculated with bacteria or exposed to vapors mimicking those around sump pumps. Corrosion rates were measured over about 30 days.

“The worst damage, with flaky iron oxide products covering corrosion, was found on steel exposed to the vapors,” NIST said. Copper sustained damage in the liquid and vapor environments but corrosion rates were slower. Steel corroded “very” slowly while immersed in the liquid mixture.

Researchers concluded that it would take about 15 years for 1.2-millimeter thick copper tube walls to develop holes from corrosion. Stress-corrosion cracking is a concern for bent copper tubing, NIST said.

A previous NIST study found that “ethanol-loving” bacteria accelerated pipeline cracking. The agency notes that “much” of the fuel infrastructure in the United States was designed for unblended gasoline. EPA Data Suggests Tank Leaks Declining.

Meanwhile, if corrosion is accelerating, it has yet to show up in the latest data from the EPA’s Office of Underground Storage Tanks (OUST). OUST suggests the number of new tank system leaks has steadily declined over the years. As of mid-fiscal 2014, there were 3,007 new releases confirmed, bringing the cumulative total to 517,317.

That’s less than half of the 6,128 new releases confirmed in full-year 2013. Over the last decade, the number of new releases reported on an annual basis has been almost cut in half.

“As a result of improved leak detection and prevention activities we continue to see the number of new releases to be significantly lower than the annual historical average number of confirmed releases,” Cliff Rothenstein, then director of OUST, wrote in a report. “In fiscal year 2003 we reported approximately 12,000 new releases, about 60% lower than the annual historical average number of confirmed releases.”


–Donna Harris, dharris@opisnet.com


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