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CORROSION OF COPPER AND STEEL ALLOYS IN A SIMULATED UNDERGROUND STORAGE TANK SUMP ENVIRONMENT CONTAINING ACID PRODUCING BACTERIA

Published

Author(s)

Jeffrey W. Sowards, Elisabeth Mansfield

Abstract

Much of the gasoline sold in the U.S. is blended with ethanol. Some components associated with underground storage tanks (UST) dispensing these blended fuels (namely the sumps containing submersible pumps) are experiencing rapid degradation due to corrosion. The corrosion is attributed to acid producing bacteria that convert ethanol in the fuel to acetic acid. In this paper, we outline a test protocol that was developed to simulate the microbial corrosion of alloys exposed to the sump conditions, which include both vapor and aqueous exposure. The lab-based test reproduced the type of corrosion observed in UST sump locations. Two cold worked alloys (110 Copper and 1018 Steel) were exposed to acetic acid producing bacteria (Acetobacter sp.) inoculated into aqueous- ethanol solutions. Corrosion rates were determined with gravimetric analysis as a function of time over the test duration of approximately 30 days. Large copper acetate crystals were observed as the primary corrosion product on the copper alloy, and the steel alloy exhibited a thick scale of oxidation products after headspace exposure. Both alloys exhibited extensive localized corrosion when the corrosion products were removed. The copper alloy was susceptible to intergranular attack and the steel alloy exhibited pitting and pearlite boundary attack when exposed to the aqueous phase. The steel corrosion rate was quite low in the acidic aqueous environment and may have been passivated by a biofilm attached to the surface. Corrosion rates of each material exposed to the simulated UST conditions are ranked as follows in order of increasing magnitude: Copper-aqueous
Citation
Corrosion Science

Keywords

Acid producing bacteria, Acetobacter sp., bioethanol, copper, corrosion rate, fuel blends, microbiologically influenced corrosion, steel.¿
Created August 29, 2014, Updated February 19, 2017