Summer 2008

UM–Duluth research assistant Jenna Bergin holds a steel “coupon” used to observe the corrosion process and collect lab samples.

UW Sea Grant Outreach

Harbor Corrosion Studies Continue 820/2008

By Kathleen Schmitt Kline

The state of Wisconsin and the federal government have earmarked a combined $410,000 to continue to address a mysterious corrosion problem affecting the Duluth-Superior Harbor and possibly other sites around Lake Superior.

The new research efforts will be coordinated by the project steering team, which includes the UW Sea Grant Institute, the Duluth Seaway Port Authority, the U.S. Army Corps of Engineers, the city of Superior, and others.

Routine inspection dives in the Duluth-Superior Harbor in 2004 revealed that steel piling is corroding at an accelerated rate when compared to other locations. While most of the steel is covered with small pits the size of a quarter, some of the steel structures had holes as large as a football. The cost of replacing all of the damaged steel is estimated to be as much as $100 million, so the project steering team is continuing a coordinated effort to determine both the causes of the accelerated corrosion and ways to mitigate the problem.

A $30,000 grant from the Wisconsin Coastal Management Program, combined with $100,000 approved by the Wisconsin Legislature and $280,000 from the U.S. Army Corps of Engineers, will fund several new tests or continuation of existing tests. While some studies will continue to probe the cause of the aggressive corrosion, others will begin to investigate ways to protect new or existing steel structures from further damage.

One such promising method for protecting the steel is the use of protective coatings. Gene Clark, coastal engineering specialist with UW Sea Grant, said the harsh Lake Superior winters will give protective coatings a difficult environment in which to work.

“The scouring action of the Lake Superior ice will probably present the biggest challenge to finding an effective coating that will stay adhered to the steel,” said Clark, who is overseeing the Wisconsin Coastal Management grant.

Because this type of rapid corrosion is rare in other freshwater harbors, Clark wants to get the word out to other Great Lakes port authorities and marina owners to examine their steel structures closely this summer while water levels remain low. Clark said “the more we get the word out about our accelerated corrosion work in the Duluth/Superior harbor, the more we are finding out that other Lake Superior facilities may also have corrosion issues. These problems may be the result of totally different causes, but the results of our work will be useful for them as well as they consider repair alternatives for their docks.”

For more information about the ongoing studies, visit

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