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Steel Corrosion Found in More Northland Harbors

Steel Corrosion by Jeff Gunderson

Steel pilings in the Duluth-Superior Harbor show pits caused by corrosion. The problem has now been found in other Lake Superior harbors and may be caused by iron-damaging bacteria.

You may have heard that steel in the Duluth-Superior Harbor has been mysteriously corroding at an accelerated rate for the past 30 years. The problem could require millions of dollars in repairs to the harbor's docks and sheet pilings. Now, experts have found that rapid corrosion is not unique to Duluth-Superior; it's in other Northland harbors as well.

"This is a much more widespread problem on Lake Superior than was understood a year ago," said Jim Sharrow, facilities manager for the Duluth Seaway Port Authority. "Similar corrosion is being discovered . . . in ports along the North Shore, as well as the South Shore of the lake."

Deeply pitted steel has been found in Two Harbors, Minn., Thunder Bay, Ont., and in the ports of Ashland and Bayfield, Wisc., as well as Ontonagon and Houghton, Mich.

Several years ago, Sea Grant partnered with the U.S. Army Corps of Engineers, corrosion experts, and others to discuss what might be boosting corrosion rates in the harbor. At that time, suspicions pointed toward changes in water chemistry. More recent efforts have focused on micro-organisms as a possible cause.
Sea Grant-funded researcher, Randall Hicks - University of Minnesota Duluth, has found bacterial communities living on the corroded steel.

"We've isolated some iron-oxidizing bacteria, and one in particular that we know . . . is similar to the type that have been implicated in the corrosion of steel in other environments," Hicks said.

Other tantalizing clues that researchers have found are:

  • River water seems to speed corrosion.

  • Cold water seems to slow it.

Wisconsin Sea Grant has received funds from the Wisconsin Department of Natural Resources and is working with the Port of Superior to explore potential solutions. Among those are coatings.

"There are all sorts of products out there, from epoxies, to paints, to tars," said Dale Bergeron, Minnesota Sea Grant's maritime extension educator. "It's easiest to apply these protective coatings to the steel before it's put in the water. To save existing steel, coastal engineers erect coffer dams, pump out the water, and apply the best coatings the project can afford."
Hicks cautions that the process of finding the cause requires patience.

"We're making progress in the lab and other groups working on this project are making great progress. We're learning more each day, but we're not going to find an answer in the next six months or years."

Danielle Kaeding, KUWS Radio, contributed to this story.

By Marie Zhuikov and Sharon Moen
May 2008

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