August 17, 2011
by ipccoating
The boom in ethanol and other biofuels may be a serious bust for the nation’s existing pipeline network, new government research concludes.
Researchers at the National Institute of Standards and Technology have found that ethanol—especially the bacteria sometimes found in it—can rapidly, dramatically degrade pipelines.
Ethanol’s corrosion potential has been hotly debated even as U.S. production has continued to soar, topping 13 billion gallons in 2010. Ethanol and bacteria are known to cause corrosion, but this is the first study of their effects on fatigue cracking of pipeline steel.
The results, presented Aug. 1 at the Department of Defense Corrosion Conference, were significant.
‘Substantial Increases’
“We have shown that ethanol fuel can increase the rate of fatigue crack growth in pipelines,” said NIST postdoctoral researcher Jeffrey Sowards. “Substantial increases in crack growth rates were caused by the microbes. These are important data for pipeline engineers who want to safely and reliably transport ethanol fuel in repurposed oil and gas pipelines.”
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NIST
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| Researcher Jeffrey Sowards reported “substantial increases in crack growth rates” by microbes in ethanol. |
Sowards’ team presented new experimental evidence that bacteria that feed on ethanol and produce acid boosted fatigue crack growth rates by at least 25 times the levels occurring in air alone.
Ethanol, an alcohol that can be made from corn, is widely used as a gasoline additive due to its oxygen content and octane rating. Ethanol also can be used as fuel by itself in modified engines. The NIST tests focused on fuel-grade ethanol.
2 Common Steels Tested
The team used a new biofuels test facility to evaluate fatigue-related cracking in two common pipeline steels immersed in ethanol mixtures, including simulated fuel-grade ethanol and an ethanol-water solution containing common bacteria, Acetobacter aceti.
The tests were performed on X52 and X70 pipeline steels, which are alloys of more than a dozen metals. Simulated fuel-grade ethanol significantly increased crack growth at stress intensity levels found in typical pipeline operating conditions, but not at low stress levels.
“The cracking is related to corrosion,” NIST said. The X70 steel, finer-grained than X52, had lower rates of crack growth at all stress levels. This was expected because larger grain size generally reduces resistance to fatigue.
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J.W. Sowards / NIST
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| A micrograph shows a crack in X52 steel after the sample was subjected to mechanical forces for several days in an ethanol solution containing acid-producing bacteria, Acetobacter aceti. Researchers at NIST’s biofuels testing facility found that the bacteria increased fatigue crack growth rates at least 25-fold, compared to what would occur in air. |
In the bacteria-laden solutions, acid promoted crack growth at stress intensity levels found in typical pipeline operating conditions.
Biocide May Help
Preliminary tests also suggested that glutaraldehyde, a biocide used in oil and gas operations, may help control bacterial growth during ethanol transport.
The findings were the first from NIST’s biofuels test facility, where material samples are installed in hydraulic test frames and subjected to load cycles while immersed in fuel inside a transparent polymer tank. Fatigue crack growth and other properties are observed over a period of up to 10 days.
NIST staff expects to continue and possibly expand the research to other potential biofuels such as butanol or biodiesel.
Collaborators at the Colorado School of Mines provided the bacteria, which were isolated from industrial ethanol storage tanks.
NIST is an agency of the U.S. Commerce Department. The ethanol research was also supported by the U.S. Department of Transportation.
Coatings Sought for Engine Corrosion
Elsewhere, research is also underway to address the corrosive effects of biofuel blends on engines.
Biofuels contain high levels of water and oxygen that have a corrosive effect on engines. There have been fears that biofuels could cause damage on car engines.
A project called Equimotor Plus aims to develop better technology, including engine coatings, to reduce corrosion, friction and wear of engines working with alternative fuels and lubricants, reports EcoSeed.org, which reports on environmental news and renewable energy technology.
The project aims to market the new technology to countries where biofuel is seen as a viable solution, the report says.
