By Cynthia Greenwood
DoD Corrosion Policy and Oversight Office
A tank barge that sank amid rough seas on January 24, 1936, in Long Island Sound carried 500,000 gallons of heating oil. To officials at the National Oceanic Atmospheric Administration, the submerged vessel, known as Cities Service Number 4, poses a serious risk of contaminating the tidal estuary should corrosion of the barge structure cause an oil leak.
The hull and rivet structure of Cities Service No. 4 is similar to the Navy battleship USS Arizona, now a hallowed tomb for 1,177 men who died when the Japanese bombed Pearl Harbor on December 7, 1941. Oil still trickles from her damaged hull, which makes the vessel an ideal subject for corrosion rate analysis.
In February, the National Park Service transferred hull and rivet pieces from the USS Arizona to the U.S. Coast Guard Academy for analysis by team of marine and environmental science majors. Three senior-level cadets are working to find parallels between the USS Arizona’s propensity for corrosion in the Pacific Rim and several wrecked vessels on the northeast Atlantic seaboard.
Last year faculty and senior-level cadets in the U.S. Coast Guard Academy’s Center for Corrosion and Materials Degradation Research became intrigued by a University of Nebraska study that analyzed the rate of corrosion on the USS Arizona hull structure.
“Because the barge has the potential to pollute and pose serious harm to Long Island Sound, we have decided to investigate the wreck using the same benign, non-destructive means that scientists and engineers have applied to the USS Arizona,” said Captain Rich Sanders, professor of chemistry at the U.S. Coast Guard Academy.
Capt. Sanders is advising the student team as they use corrosion rates developed for the USS Arizona. “Specifically we are determining the corrosion rates of metals in seawater by constructing Tafel plots,” said Dylan Finneran, the cadet team leader. “We expect these corrosion rate models to help us and the Coast Guard understand the potential for structural degradation on other submerged vessels in Coits Cove near New London, Connecticut.”
Cadet research into corrosion rates on wrecked vessels is one of several projects underway at the Center for Corrosion and Materials Degradation Research. The Center’s faculty and cadets benefit from funding provided to the Technical Corrosion Collaboration, a program sponsored by the Department of Defense Corrosion Policy and Oversight Office to help universities broaden their corrosion science and engineering research, and educate students in ways that will benefit the Coast Guard and DoD.
In studying the Arizona and Cities Service No. 4, Finneran has teamed with fellow cadets, Christian Von Stralendorff and Jamie Waterman, to probe key questions about galvanic corrosion that are frequently addressed by materials scientists who analyze structural degradation on older military and commercial ships.
The team has posed several questions: Do interactions between component metals of a riveted hull produce, impact, or influence corrosion processes on the Arizona? By extension, might hull plate and rivet interactions occur on other vessels? If so, are they a cause for concern?
In the lab this spring, the cadets have begun determining corrosion rates of metal samples in seawater using potentiostats. These are electronic devices that push and pull electrons into and out of metal while measuring the production of electrical current. “The cadets are now in the process of developing and refining their experimental procedures and techniques to yield reproducible corrosion rate data consistent with what is reported in the literature,” Capt. Sanders said.
The cadets will also examine the influence of temperature, salinity, dissolved oxygen, and pH upon corrosion rates. “These results, again referenced against the literature, will be useful to the cadets as they evaluate corrosion rates using sea water samples collected from various locations and depths, and at different times of the year,” noted Capt. Sanders.
“Manipulating these variables may prove useful as cadets explore seasonal influences on corrosion rates, model estuarine conditions, and probe other factors such as hypoxic water, bio-fouling, or sedimentation which could alter oxygen levels and pH,” Capt. Sanders said.
Over the long term, the team will test hull and rivet coupons from other vessels constructed in the early twentieth century, including the Coast Guard Academy’s own training ship. “At this time we are preparing samples from the USCG Cutter Eagle, and we will be fortunate to learn firsthand something about the steel used to build her,” said Finneran. “We will evaluate samples from other sources as we identify and acquire them.”
”Besides giving cadets an opportunity to do fieldwork on shipwreck sites, this research allows them to be part of a broader Coast Guard effort to assess environmental threats posed by sunken vessels, and to increase their understanding of corrosion and its widespread impact, ” said Capt. Sanders.
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