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New Bay Bridge May Be Under Microbe Attack

Tuesday, January 30, 2018

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According to a report from a San Francisco-area television news station, the new span of the San Francisco-Oakland Bay Bridge is experiencing corrosion at unexpected rates, possibly brought on by microbes.

Bay Bridge
Dllu, CC BY-SA 4.0, via Wikimedia Commons

The new eastern span of the San Francisco-Oakland Bay Bridge, which opened less than five years ago, is exhibiting signs of microbiologically influenced corrosion.

NBC Bay Area’s investigative unit reported Thursday (Jan. 25) that the California Department of Transportation is looking into why pitting appears to be afflicting welds on the piles securing the new eastern span in the bay floor. The new bridge cost $6.4 billion to build, opened in 2013 and has been subject to scrutiny over cost overruns and potential material deficiencies in the years since.

MIC on Bridge Piles

The latest problem, corrosion that Caltrans says is proceeding at an accelerated rate in some areas, could potentially cut the bridge’s projected 150-year service life by a third, NBC reports. The station acquired public records indicating that Deepwater Corrosion Services Inc., of Houston, inspected piles that were covered in barnacles, finding that under the biofouling was pitting corrosion that appears to be more serious than anticipated.

Caltrans told the station it is investigating whether microbes in the bay could be responsible for the corrosion. Microbiologically influenced corrosion (MIC) is common in structures such as wastewater facilities and sewers, where bacteria convert hydrogen sulfide gas into sulfuric acid, which speeds corrosion. While MIC is less prevalent on bridge projects, NBC reports that the study indicated that there are microorganisms on the bay floor that could speed corrosion.

Bay Bridge

Caltrans is looking into why pitting appears to be afflicting welds on the piles securing the new eastern span in the bay floor.

The corrosion on the bridge’s 13 piles, according to the news station, could reduce the bridge’s service life by up to 50 years.

Caltrans did not immediately respond to a request for a copy of the Deepwater Corrosion report on Monday (Jan. 29).

Past Project Problems

After the completion of the new span in 2013, several reports of issues with the structure surfaced. In 2014, corrosion was found on cable strands; the same year, water intrusion was found in an area that was supposed to be watertight.

In 2015, cracking was found on improperly grouted anchor rods, and last year, Caltrans defended the bridge’s materials after reports that discarded steel from the project showed yield strengths lower than what was required on the job.

The old eastern span of the Bay Bridge was replaced due to concerns about its safety under earthquake conditions; part of the span infamously collapsed during 1989’s Loma Prieta earthquake, killing one driver. While the western span—a suspension bridge reaching from San Francisco to Yerba Buena—was retrofitted for seismic durability, Caltrans determined that the eastern span should simply be replaced.


Tagged categories: Bridges; Caltrans; Corrosion; Microbiologically Induced Corrosion (MIC)

Comment from Fred Wittenberg, (2/4/2018, 7:45 PM)

Hydrogen sulfide is anaerobic. S.F.Bay isn't a sewer, so why isn't there enough oxygen in it? I've commented before regarding the problems with this bridge; and they just keep occurring?

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