Accelerated Corrosion of Piers in the Duluth Harbor

Project summary:

Shipping in the Duluth-Superior harbor, the largest port in the Great Lakes, has a $200-million annual impact on Minnesota's economy. The steel sheet piling used in the port's docks, bridges, and bulkheads is corroding at a rate not seen in other Great Lakes ports. Replacing the 20 kilometers of these structures may cost more than $100 million if the cause and possible remedies for this corrosion cannot be identified. In this project, through field and laboratory studies, University researchers worked with the Duluth Seaway Port Authority and the U.S. Army Corps of Engineers to determine the potential role played by microbial consortia in the accelerated corrosion process. Twelve possible causes of corrosion were initially identified and ranked by an expert panel, which established that water chemistry, dissolved oxygen content, and dissolved chlorides from de-icing salts were most likely to be responsible for the accelerated corrosion, although it was unclear whether microbiological factors or functional harbor changes were disproportionately influencing corrosion in the harbor. Later data found that corroding steel structures in the Duluth-Superior harbor are covered by complex microbial biofilms containing bacteria of the type responsible for corrosion of steel in other environments. This knowledge will be useful in assessing, repairing, protecting, and replacing steel structures in other Great Lakes ports, as well as aiding in the development of control and prevention strategies and practices. Full results of the study were published in the July 2009 issue of the CURA Reporter.