Ethanol-loving bacteria accelerate cracking pipeline steels, finds NIST

Ethanol-loving bacteria accelerate cracking of pipeline steels, finds NIST

11:44 AM, 8th August 2011
Ethanol-loving bacteria accelerate cracking of pipeline steels, finds NIST
Micrograph of crack in X52 steel, subjected to mechanical forces for several days in an ethanol solution containing acid-producing bacteria, Acetobacter aceti. NIST researchers found that the bacteria increased fatigue crack growth rates at least 25-fold compared to what would occur in air.


GAITHERSBURG, US: The produciton of ethanol in US, for fuel has been rising quickly, topping 13 billion gallons in 2010. Existing gas pipelines might be an efficient alternative for moving this renewable fuel around the country. But researchers at the National Institute of Standards and Technology (NIST) caution that ethanol and especially the bacteria sometimes found in it, can dramatically degrade pipelines.

At a recent conference, NIST researchers 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 occuring in air alone.

The NIST team used a new biofuels test facility to evaluate fatigue-related cracking in two common pipeline steels immersed in ethanol mixtures, containing common bacteria, Acetobacter aceti. Ethanol and bacteria are known to cause corrosion, but this is the first study of their effects on fatigue cracking of pipeline steels.

“We have shown that ethanol fuel can increase the rate of fatigue crack growth in pipelines,” said Jeffrey Sowards, Postdoctoral Researcher, NIST. “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.”

The NIST tests focused on fuel-grade ethanol. 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. In the bacteria-laden solutions, acid promoted crack growth at stress intensity levels found in typical pipeline operating conditions.

Preliminary tests also suggested that glutaraldehyde, a biocide used in oil and gas operations, may help control bacterial growth during ethanol transport.

The NIST staff expect 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. The research was supported by the US Department of Transportation.

J W Sowards, T D Weeks, J D McColskey, C Williamson, L Jain and J R Fekete, presented at DOD Corrosion conference 2011, at La Quinta, on August 1, 2011. The topic was ‘Effect of ethanol fuel and microbiologically influenced corrosion on the fatigue crack growth behaviour of pipeline steels.’

(C) National Institute of Standards and Technology News




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