kenvlach
Materials
- Apr 12, 2000
- 2,514
Chicago Tribune, Nov. 25, 2005
By John McCormick, Tribune staff reporter
[free registration required]
"DULUTH, Minn. -- A mystery lurking below the harbor surface here has engineers and scientists debating how to slow the abnormally rapid corrosion that now threatens the long-term structural integrity of the largest port on the Great Lakes.
The corrosion--at a rate believed to be 2 to 10 times faster than expected--is taking place on an estimated 13 miles of steel plates that line the harbor, metal that provides support for bridges, iron ore loading docks and other vital structures.
Theories abound about the cause, ranging from stray electrical currents to road salt runoff to zebra mussels. Lower levels of harbor pollution may also be speeding the corrosion process because there is more dissolved oxygen in the water.
"They are suffering some severe corrosion," said Rudolph Buchheit, a material science and engineering professor at Ohio State University who is studying the problem. "But it is not at all agreed upon why this is happening."
While salt water is known to attack untreated steel, experts say the rate of rust in the fresh water of Duluth-Superior Harbor is unlike anything they have seen on the Great Lakes.
Buchheit said some steel plates that are a half-inch thick or more have been perforated in less than 10 years. "To make it through that thick a material in just a few years is a significant corrosion rate," he said.
After assembling a panel of experts, the U.S. Army Corps of Engineers issued a report this year that said the problem could cost more than $100 million to correct if major replacement of the steel pilings is required.
Some possible causes were ruled out, while additional study was suggested for others. Top theories identified by that report include environmentally influenced changes in water chemistry, microbe activity, dissolved chlorides from deicing salts and rising levels of dissolved oxygen.
Also under consideration are zebra mussels, which could protect some steel while concentrating corrosion at other water depths. Still, large mussel colonies did not develop here until the late 1990s, well after it is believed the corrosion began.
The corrosion has pitted steel throughout the harbor, primarily near the water line and tapering off at about 10 feet below the surface. The individual pits are often about the width of a dime and in some places their abundance is weakening the steel, which is used to reinforce the land and make deep-water channels possible.
...
"The increased rate of corrosion here is believed to have started in the late 1970s, when several significant changes were made to the harbor and surrounding areas.
For one, a new wastewater treatment plant went online in 1978, consolidating the area's industrial and municipal discharges and potentially increasing the harbor's dissolved oxygen while also concentrating the discharge of industrial chemicals.
The Corps of Engineers report also lists the start of filtering for asbestos in the 1970s at Duluth's water treatment facility, a process that added aluminum sulfate to the water and is known to have caused corrosion in the water lines.
Although it was also discovered that some of Duluth's water mains were corroding for other reasons, some have speculated that whatever caused the deterioration of the water lines was transferred to the harbor through the wastewater treatment plant.
"It is probably some combination of factors that are unique to this harbor," said Jim Sharrow, facilities manager for the Duluth Seaway Port Authority.
...
"I have worked at facilities all across the Great Lakes and I have never seen anything like this," said Chad Scott, an engineer and professional diver who was the first to notice patches of significant corrosion in the harbor in the late 1990s.
...
"Some companies are experimenting with protective coatings that can be applied to the steel, an expensive proposition considering the work must be done after surrounding water is blocked and then drained away.
Scott said he expects it will take about five years to collect the data needed to fully understand the corrosive effect of the harbor's waters.
..."
*************************
Any comments? Any similar, seemingly unexplained cases of accelerated corrosion of steel?
Any clever techniques for cleaning the steel & stopping further corrosion in situ?
The ASM Handbook, Volume 13B, Corrosion: Materials (available December 31, 2005) that I have on order may be already obsolete!?
Ken
By John McCormick, Tribune staff reporter
[free registration required]
"DULUTH, Minn. -- A mystery lurking below the harbor surface here has engineers and scientists debating how to slow the abnormally rapid corrosion that now threatens the long-term structural integrity of the largest port on the Great Lakes.
The corrosion--at a rate believed to be 2 to 10 times faster than expected--is taking place on an estimated 13 miles of steel plates that line the harbor, metal that provides support for bridges, iron ore loading docks and other vital structures.
Theories abound about the cause, ranging from stray electrical currents to road salt runoff to zebra mussels. Lower levels of harbor pollution may also be speeding the corrosion process because there is more dissolved oxygen in the water.
"They are suffering some severe corrosion," said Rudolph Buchheit, a material science and engineering professor at Ohio State University who is studying the problem. "But it is not at all agreed upon why this is happening."
While salt water is known to attack untreated steel, experts say the rate of rust in the fresh water of Duluth-Superior Harbor is unlike anything they have seen on the Great Lakes.
Buchheit said some steel plates that are a half-inch thick or more have been perforated in less than 10 years. "To make it through that thick a material in just a few years is a significant corrosion rate," he said.
After assembling a panel of experts, the U.S. Army Corps of Engineers issued a report this year that said the problem could cost more than $100 million to correct if major replacement of the steel pilings is required.
Some possible causes were ruled out, while additional study was suggested for others. Top theories identified by that report include environmentally influenced changes in water chemistry, microbe activity, dissolved chlorides from deicing salts and rising levels of dissolved oxygen.
Also under consideration are zebra mussels, which could protect some steel while concentrating corrosion at other water depths. Still, large mussel colonies did not develop here until the late 1990s, well after it is believed the corrosion began.
The corrosion has pitted steel throughout the harbor, primarily near the water line and tapering off at about 10 feet below the surface. The individual pits are often about the width of a dime and in some places their abundance is weakening the steel, which is used to reinforce the land and make deep-water channels possible.
...
"The increased rate of corrosion here is believed to have started in the late 1970s, when several significant changes were made to the harbor and surrounding areas.
For one, a new wastewater treatment plant went online in 1978, consolidating the area's industrial and municipal discharges and potentially increasing the harbor's dissolved oxygen while also concentrating the discharge of industrial chemicals.
The Corps of Engineers report also lists the start of filtering for asbestos in the 1970s at Duluth's water treatment facility, a process that added aluminum sulfate to the water and is known to have caused corrosion in the water lines.
Although it was also discovered that some of Duluth's water mains were corroding for other reasons, some have speculated that whatever caused the deterioration of the water lines was transferred to the harbor through the wastewater treatment plant.
"It is probably some combination of factors that are unique to this harbor," said Jim Sharrow, facilities manager for the Duluth Seaway Port Authority.
...
"I have worked at facilities all across the Great Lakes and I have never seen anything like this," said Chad Scott, an engineer and professional diver who was the first to notice patches of significant corrosion in the harbor in the late 1990s.
...
"Some companies are experimenting with protective coatings that can be applied to the steel, an expensive proposition considering the work must be done after surrounding water is blocked and then drained away.
Scott said he expects it will take about five years to collect the data needed to fully understand the corrosive effect of the harbor's waters.
..."
*************************
Any comments? Any similar, seemingly unexplained cases of accelerated corrosion of steel?
Any clever techniques for cleaning the steel & stopping further corrosion in situ?
The ASM Handbook, Volume 13B, Corrosion: Materials (available December 31, 2005) that I have on order may be already obsolete!?
Ken
