EFFECT OF ETHANOL FUEL AND MICROBIOLOGICALLY INFLUENCED CORROSION ON THE FATIGUE CRACK GROWTH BEHAVIOR OF PIPELINE STEELS

Ethanol fuel production and consumption are expected to increase significantly in the near future.  Existing pipeline infrastructure could be repurposed to transport ethanol and other biofuels from production sources, such as those located in the Midwest, to end users across the country.  The effects of ethanol fuel, including its ability to harbor corrosion-inducing microbiological life, are not well established in relation to degrading the fatigue properties of pipeline materials.  In this work experiments were performed to evaluate crack growth behavior of pipeline steels in several ethanol environments.  The environments included a simulated fuel grade ethanol and an ethanol-water solution inoculated with a microbiological species (Acetobacter aceti) isolated from industrial ethanol storage tanks.  Fatigue crack growth rates of API 5L X52 and X70 pipeline steels were determined as a function of the stress intensity amplitude (ΔK) during exposure to the various ethanol environments.  Significant increases in fatigue crack growth rate were found above ΔK levels of approximately 17 MPa·m^1/2 and 20 MPa·m^1/2 during testing of X52 and X70 in simulated fuel grade ethanol, respectively.  Fatigue crack growth rates were increased by two orders of magnitude, relative to air, during testing of X52 and X70 in ethanol-water solutions inoculated with acetic acid producing bacteria.  Concurrent research suggested that glutaraldehyde may be an effective biocide for controlling acid producing bacteria in pipelines.  The data presented are useful for reliability models to ensure safe fuel transport of ethanol.