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Bacteria Causes Corrosion at Seattle Dock

Tuesday, January 8, 2019

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Washington State Ferries recently reported that an unknown organism is causing accelerated corrosion on steel pilings being used in work on the Colman Dock in Seattle. The pilings will be used to support the dock’s new ferry terminal for the next 75 years.

In June, during routine monitoring, workers saw bright orange corrosion on steel piles near the waterline, WSF spokesperson Broch Bender told the Kitsap Sun.

Steel Pile Corrosion

According to the Washington State Department of Transportation, WSF is replacing “aging and seismically vulnerable” pieces of Colman Dock. Other work on the dock includes replacing the existing timber trestle portion with a new concrete and steel trestle, and replacing the main terminal building, among other measures.

WSF reports that while familiar with what bacteria causes corrosion in Puget Sound, this bacteria is unknown, according to Bender.

In order to mitigate further issues caused by corrosion, a high-performance marine coating system will be applied to the dock pilings. How much the coating will cost has not yet been determined. WSDOT has also kicked off a 20-month study to monitor existing, untreated piles; the study will indicate whether the piles will last their intended 75-year lifespan, and will also report on how to treat the existing structures.

With accounting for corrosion, the piles were designed thicker to meet the intended lifespan. WSF began pile-driving work in October 2017, and 500 piles will be used to support the new ferry terminal.

Each pile is 150 feet long, with the first 138 feet driven into Elliott Bay during construction by a vibratory hammer until secure.  Roughly 24,000 tons of creosote piles and timbers are to be removed from the bay during construction work.

A combination of $373 million dollars in federal, state and local funding has been garnered for the project to date.


Tagged categories: Corrosion; Infrastructure; Marine; NA; North America; Quality control; Quality Control

Comment from Tony Rangus, (1/8/2019, 10:08 AM)

Wonder what the estimated corrosion rate at the water line was postulated to be? I suppose that a cost analysis was performed to look at extra thickness versus coatings & coatings maintenance costs. Be interesting to see that comparison!

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