Abstract
Changes in design and operational practice have resulted in a number of failures of copper-nickel components in seawater systems that have been attributed to exposure to sulfide-polluted, stagnant seawater during shutdowns. This has generated interest in the development of online corrosion monitors for these systems. In order to assess electrochemical frequency modulation for this role, 90/10 and 70/30 copper-nickel specimens were exposed to flowing seawater until protective films were developed. Some specimens were then buried in decaying organic debris at the bottom of the tank. These specimens were re-exposed to flowing seawater after remaining in the sediment for 55 days. Corrosion rates were monitored throughout the experiment using three different electrochemical techniques. Electrochemical frequency modulation confirmed earlier work showing that copper-nickel alloys experienced high corrosion rates in clean seawater after exposure to decaying organic debris. The technique, supported by electrochemical impedance measurements, also indicated that the corrosion rate was generally not under diffusion control. The corrosion rate was found to be profoundly influenced by the amplitude of the applied voltage. However, the technique highlighted changes in the corrosive environment and changes in the corrosion mechanism, indicating that it has potential as an online monitoring technique.
