Freshwater Corrosion in the Duluth-Superior Harbor: Summary of Initial Workshop Findings, 9 September 2004

Abstract : This report reviews the potential causes of accelerated corrosion of sheet pile and other steel structures in the Duluth-Superior Harbor (DSH) and makes recommendations for addressing the problem. To determine the cause of the accelerated corrosion reported at DSH, the Duluth Seaway Port Authority sought external assistance from experts working within both the public and private sectors. To provide a forum for discussion and technical information exchange, the port authority organized a workshop featuring scientists and engineers with expertise in corrosion processes, materials, and corrosion protection technologies. The authors met in Duluth in September 2004 to examine harbor corrosion and consult with interested parties. The corrosion appears as pock marks primarily in the 4 feet just below the water surface. The corrosion extends down to about 10 feet, but decreases from 4 feet below the surface to 10 feet. The corroding pock marks are covered by an orange-colored coating that tends to cover the corroded pit. Water chemistry, dissolved oxygen content, and dissolved chlorides from de-icing salts seem to be the most likely agents of accelerated corrosion of 12 causes discussed. A lack of data made it unclear whether microbiological factors or functional harbor changes are unduly influencing corrosion in the harbor. The authors recommend immediately quantifying the corrosion rate, conducting a water chemistry analysis, checking for microbiologically influenced corrosion, testing for stray DC currents, and assessing the condition of critical steel structures. They encourage long-term monitoring of corrosion in the Duluth-Superior Harbor and other Great Lakes ports, as well as developing a condition-based strategy for steel replacement and repair.