Rare steel corrosion in Lake Superior harbor ‘most interesting issue I’ve ever worked on’
Since the 1970s, the rate of steel corrosion in Lake Superior has been on an upward slope. On Wednesday, Feb 8, a group of about 40 people met at the Barkers Island Inn in Superior, Wisconsin, to learn about what is affecting the Duluth harbor’s almost 14 miles of steel sheet piling.
At the event, two experts went over the issues occurring in the Lake Superior. Gene Clark of University of Wisconsin Sea Grant Institute is one of the men in charge of this research topic.
“It’s the most interesting issue I’ve ever worked on,” Clark said. “The more we investigated it, the more questions we had.”
The other expert on the topic is Chad Scott of AMI Consulting Engineers. Scott is the man who discovered the issue of steel corrosion in the harbor, by diving in the lake and examining the steel. When Scott first discovered the problem in the late 1990s, he had problems with people believing the issue was so big.
“We couldn’t convince the people that we had a problem,” Scott said. “If it was built before the mid 1980s, it will have at least some corrosion on it.”
The fact that the corrosion is occurring in a fresh water lake was baffling for both the marine experts.
“It’s not common in freshwater lakes,” Clark said. “The steel can be a century old in the other great lakes and have hardly and corrosion.”
After weighing numerous options to why they felt this could be happening, the experts determined that there is iron oxide that is corroding the steel.
“The clean water could make a better environment for the iron oxide to corrode the steel in the harbor,” Clark said.
The industries that put in these steel pieces throughout the harbor are the ones that are getting hurt the most from the corrosion, because they are the ones paying for it. To completely replace a steel sheet costs $3,500 per foot, but to have Scott and his dive team fix the steel costs between $1,300-$1,500 per foot.
To try and fix the problem, or at least delay the process of corrosion, Scott and his team are putting a new type of epoxy coating on the steel that is supposed to extend the lifetime of the steel another 50 years.
It has been a long process to find a way to successfully halt the corrosion for the time being. There have been ways to stop corrosion in the past, but the majority of those ways only work in a warmer climate where there isn’t ice slamming into the steel.
“The problem is we have heavy ice,” Scott said. “We had to find something durable enough to protect from the corrosion, and durable enough to take impacts from the ice being pushed into the structures by the ships in the harbor.”
So far, the new coating has held its own out in the harbor of Lake Superior. The steel is still corroding, and the industries are beginning to weigh the different options to protect their steel.
“Some manufacturers are looking at new types of steel, corrosion resistant steel, a couple different types of treatments and composite piling,” Scott said.
The problem of steel corrosion doesn’t seem like it is going anywhere in the near future. However, both Scott and Clark are trying to get to the bottom of the issue.
“While the scientists are still working to identify those strains of bacteria most likely to be causing the problems, our solutions are keeping the port infrastructure safe from further deterioration,” Clark said via email. “It has been a very satisfying problem to be involved with finding useable solutions.”