Abstract
During a recent renovation of the USS Constitution, extensive corrosion was discovered in bands around a number of copper treenails used to hold the wooden planks and strokes to the frames. Four treenails were evaluated at the Carderock Division, Naval Surface Warfare Center. Chemical and metallurgical analysis was conducted on the copper treenails, and x-ray diffraction analysis was performed on corrosion products and scrapings from near the treenails. The corrosion was found to be caused by metal ion concentration cells between areas in the wood and areas between wooden pieces, enhanced by the presence of microbiologically-generated sulfides. The treenails were determined to be at least 125 years old. The attack is likely to continue, and little can be done to mitigate the problem short of changing the treenail material or coating them before insertion, both of which would be very expensive and historically inaccurate. Since the rate of attack is fairly low, on the order of 1-mil/yr, no action is recommended short of performing ultrasonic inspections and replacing badly corroded treenails whenever there is access to the treenail heads during future restorations.
