Harbor steel corrosion and the solution to an expensive problem

The presence of freshwater steel corrosion in the Duluth Harbor has been a point of interest for many since as early as 1998. The River Talks, in their fourth year, remain as informal speaker series about the St. Louis River Estuary in Duluth-Superior. The group met this month to discuss freshwater steel corrosion in the harbor and the efforts of various individuals and groups to research and correct the problem.

“Everywhere that had steel was being affected,” said Chad Scott founder of AMI Consulting Engineers in Duluth, MN. Scott discovered that all steel structures in the Duluth harbor were suffering from severe steel corrosion that had rarely been seen in freshwater ports until his discovery. The problem was came to light back in 1998 when Scott found evidence of steel corrosion on various dives in and around the harbor. Scott immediately came to the conclusion that “We can never cure this” when the extent of the damage became evident. With this in mind Chad Scott and Gene Clark with the University of Wisconsin Sea Grant Institute looked into finding the root of the problem and any possible solutions that might save the harbor’s steel. The problem of freshwater corrosion is unique in that “the corrosion that is being seen in Lake Superior today is what is usually found in saltwater” said Gene.

With the uniqueness of the problem in mind the duo began to look at the problem with experts from around the world to discover the cause of the steel corrosion in the harbor. Dr. Randall Hicks, a professor at The University of Minnesota Duluth was one of the experts that became part of the research team. Hicks discovered iron-oxidizing bacteria in samples from the steel in the harbor taken on dives. This discovery led to the realization that the freshwater corrosion was a result of ice aberrating away the steel when it was crushed against the copper deposits that were left behind by the bacteria.

Photo: Wisconsin Sea Grant

Scott went on to discuss their solutions to the problem saying, “most of the solutions we have today are for environments that wouldn’t see ice.” So finding a way to protect the remaining steel in the harbor became the group’s main focus after their initial discovery of the root of the problem. Finding a material that would protect the harbors steel while also being resistant to the abuse that ice inflicts on harbor structures was one of the main struggles the group faced in finding a solution.

Eventually Scott and his team came up with a solution “that could take the abuse.” The team with their solution in mind has recently finished applying the it to various structures that are found in the Harbor. The solution included erosion preventative hybrid epoxy coating that was researched and implemented effectively. The coating is durable and prevents bacteria from getting at the steel while also being durable enough to take the abuse from the crushing ice. The solution “is intended to last another 50 years,” said Scott. Many industries in the harbor have benefited from the research done by UW sea grant and there remains a critical need to assist Great Lakes ports, harbors and marina managers and owners with issues identification in the future.

Sources:

Chad Scott- AMI Consulting Engineers

(218) 727–120 6or chad.scott@amiengineers.com

Gene Clark- Wisconsin Sea Grant

715–392–3246 or gclark1@uwsuper.edu

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