Corrosion analyses of iron and steel archaeological shipwreck sites

Great Britain and the United States were, in turn, the world\u27s leading maritime powers during the nineteenth and early twentieth centuries. Comprehensive historical and archaeological analyses of ship construction practices among these countries, therefore, reveal the predominate types of iron and steel vessels that were built during this time. There are limited data available, though, that infer the corrosion behavior of iron and steel vessels over historical timescales. The author performed minimal-disturbance corrosion analyses on two shipwrecks located in Bermuda. These surveys represented the first time that in-situ corrosion testing was ever performed on shipwrecks in the region. The in-situ corrosion behavior of archaeological iron and steel shipwrecks had also never been compared against either standardized or replicated marine conditions. The author, therefore, completed a series of laboratorial potentiodynamic polarization scans on reference steel samples that were placed in a series of synthetic marine environments. Overall, the potentiodynamic polarization scans showed that such controlled laboratorial experiments could not be adequately utilized to infer the approximate degradation rates of archaeological iron and steel shipwrecks. The best way to achieve a more comprehensive understanding of shipwreck corrosion behavior would be to focus solely on in-situ data collected from a relevant site. The in-situ investigations also implied that for archaeological iron and steel shipwrecks corroding in the shallow, subtropical waters of Bermuda, more iron, once displaced from the underlying oxide-based layers, is leaching directly into the seawater instead of forming more stable compounds within the exterior calcareous concretion layers. Corrosion product layers, therefore, cannot be solely utilized to infer the actual corrosion rates of archaeological iron or steel shipwrecks in Bermuda. A combination of direct in-situ electrochemical measurements and mass spectrometry analyses also determined that certain areas of a respective archaeological iron or steel shipwreck might corrode at different rates. The laboratory-based potentiodynamic polarization analyses and the in-situ investigations did not specifically consider the possibility that microbiologically influenced corrosion in natural seawater might eventually mitigate longer-term corrosion processes on archaeological iron or steel artifacts. The effects of microbial metabolism on iron or steel shipwreck corrosion behavior, therefore, would mean that the corrosion behavior among multiple vessels, even if they featured a similar construction methodology and sank in close proximity, would be distinct for each site. The determination of an archaeological iron or steel vessel\u27s specific corrosion rate may therefore require more intrusive and expensive survey techniques, such as the complete coring of hull plates