Pits pose problem in port
By Peter Passi
Duluth News Tribune
Something is gnawing away at the harbor's very foundations
in Duluth and Superior, and no one knows exactly what
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
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
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
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
"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
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
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
"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,
"There are a number of improvements people probably
will still have to make."