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Great Lakes Article:

Pits pose problem in port
By Peter Passi
Duluth News Tribune
08/07/03


Something is gnawing away at the harbor's very foundations in Duluth and Superior, and no one knows exactly what it is.

During an underwater inspection in 2000, diver and structural engineer Chad Scott first noted mysterious pits forming in the steel pilings that gird the port's shore, docks and loading facilities.

In the past few years, Scott, an employee of Krech Ojard & Associates, a Duluth-based engineering firm, has monitored the advancing damage, watching it steadily munch deeper into the steel. Now, the harbor's bulwarks are peppered with irregularly shaped craters, many as wide as three-quarters of an inch and as deep as one-quarter of an inch.

To put that in perspective, consider that much of the original sheet piling used to support the harbor's shoreline was just three-eighths to half an inch thick.

"We have a fairly short window of time in which to do something," said Jim Sharrow, facilities manager for the Duluth Seaway Port Authority. If the corrosion goes unchecked, many of the port's docks and structures could be so badly compromised within five to 10 years that they would require replacement. And that would be very expensive.

Sharrow estimates that the Port Authority alone would need to spend more than $13 million to replace about 9,000 lineal feet of plate piling on its docks.

The implications for the overall port are even more grave. When public and private structures are considered as a whole, Sharrow estimates that the port contains more than 60,000 feet of plate piling. Replacing it all would cost nearly $100 million.

"It's a serious problem," said John M. Larson, acting area engineer for the U.S. Army Corps of Engineers. "We need to come up with a way of protecting these structures."

Right now, however, Larson acknowledged that people are at a loss for a remedy.

"We really don't know very much about what exactly this corrosion is or why it's occurring," he said. "As far as we can tell, it seems to be unique to this harbor."

Scott has dived other Great Lakes structures, including facilities in Two Harbors and Taconite Harbor, but nowhere else exhibits pitting on par with what he has seen in the Twin Ports.

Some Port of Duluth-Superior businesses can't wait for a remedy. They have already found it necessary to shore up corroded steel.

Fred Schusterich, president of Midwest Energy Resources Co., which operates a terminal in Superior, said about 1,000 steel H-beams support the dock his company uses to load coal onto ships. In recent years, Midwest has braced 200 to 300 of those beams by jacketing them with concrete-filled pipe. Schusterich said the company will continue to make improvements needed to keep its dock structurally sound.

"It's a challenge any time you make a capital expenditure like that that you hadn't planned for," he said.

While steel corrosion has long been a fact of life in saltwater ports, Scott said many people are dumbfounded by what is occurring in the Twin Ports.

"People never thought that corrosion would be much of a problem in a freshwater port," he said. "They didn't realize that corrosion in fresh water can be just as bad, if you have the right conditions."

Just what conditions have led to the local damage remains unclear, however.

Recently, the Duluth Seaway Port Authority asked the U.S. Army Corps of Engineers to help solve the mystery.

"The Corps has the people who can do a good lakewide study to see what this is and whether it's happening anywhere else," said Adolph Ojard, executive director of the Duluth Seaway Port Authority.

Larson agreed that the situation deserves study, but no money has been set aside for the task. A district engineer has been briefed on the situation, however, and will consider the request.

Larson said it's difficult to know what a study would cost until specific parameters can be drawn up.

Scott has found corroded steel in Duluth's harbor at water depths as great as 12 feet, but the worst damage is typically to be found within three to four feet of the water line.

Steel structures installed 25 to 30 years ago display damage similar to that found on much older steel in the harbor. Meanwhile, steel installed more recently shows corrosion that appears to be directly proportional to its length of exposure to the harbor's water.

Subsequently, Scott has concluded that the corrosion is a recent phenomenon, dating back about 25 to 30 years.

"At about that same time, we had some major water quality changes, as the government started regulating pollutants more strictly," Scott said.

Improved water quality, while good for the river's biology, may have played a role in touching off corrosion, he said he believes.

"Clean water can take up more dissolved oxygen, and oxygen can be one of the primary ingredients for corrosion," he said, cautioning, "Of course, all this is in the theoretical stages right now."

Scott said other possible factors in the corrosion could include acidity, metallurgy, marine biology, pollutants, ice scouring and even water temperatures.

"This is no cosmic mystery," Shusterich said. "I think good hard science should be able to help us identify the problem."

But a solution may come too late for many structures, he said.

"There are a number of improvements people probably will still have to make."

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