Duluth-Superior Harbor Corrosion

In 2004, a study began in the Duluth-Superior harbor which looked at the accelerating rates of corrosion happening on steel sheet pilings. These steel sheet pilings make up not only docks, but also piers, retaining walls, and loading facilities. Now you may ask, “Why is this something I should be worried about?”

Example of steel corrosion

Good question. This problem is not only detrimental to the harbors ecosystem, but also leaves taxpayers wondering how this problem can be solved and paid for. “Within the harbor, there is over 14 miles of steel sheet piling,” explained coastal engineering specialist Gene Clark.

Now given that there is such a great amount of steel which is experiencing corrosion at accelerated rates, it leaves groups like Wisconsin Sea Grant and the Duluth Seaway Port Authority searching for ways to help slow down the rate to avoid having to replace the steel all together.

In an article on the Wisconsin Sea Grant website titled “Discovery of the Problem and Early Work”, it explains the situation in the following manner. “If the problem remained unaddressed, the structural integrity of docks and loading facilities could be compromised and the failing steel would have to be replaced at a cost of $1,500 or more per lineal foot. The Duluth Seaway Port Authority estimated there could be $90 to 100 million of possible repairs due to corrosion-weakened steel.”

Clearly this isn’t pocket change, and its going to take some extensive research to present a plan of attack to the state in order for funding to be received. This is where Chad Scott of AMI Consulting Engineers comes into the picture. Scott began his career diving out on the east coast inspecting docks for corrosion damage. When this problem was first addressed, it was his team of divers who went down to inspect the underwater steel pilings in the Duluth-Superior Harbor.

Now what is is most interesting to me was when he explained he had never seen corrosion of this kind. “When I completed my first dive, you would have thought that this steel had been in salt water,” said Scott. The harbor consists of freshwater, so how could it be that corrosion to steel was happening at such an accelerated rate?

There are a few possible causes listed in the article “Great Lakes Accelerated Freshwater Harbor Corrosion” which was published by the UW Sea Grant Institute. The harbors water chemistry might have changed in a way that promotes corrosion. Microorganisms like bacteria or fungi could be eating away at the steel. The harbors change in rate of ship traffic, types of cargo ships and various harbor modifications.

So how is this problem being addressed and what sort of ideas are being implemented to help reverse corrosion? Scott and his team were able to collaborate with the NRRI along with epoxy manufactures to come up with a product designed for jacketing pipe piles and H piles.

H-Piles jacketed with epoxy

These jackets don’t necessarily stop the corrosion, but they help maintain the steel’s shape from bending and collapsing. Though this problem is still under research today, hopefully these epoxy jackets can not only save time for the steel, but also until a final solution can be made to address this serious issue.