Detection of Selective Phase Corrosion of Nickel Aluminum Bronze in Seawater by Electrochemical Frequency Modulation

Components made from cast nickel aluminum bronze have been used extensively in some seawater systems because of their generally good toughness. However, this alloy can be susceptible to selective phase corrosion (SPC). This has led to requirements for removal of components on a fixed timetable to test for the presence of this corrosion. Significant savings in cost and labor could be achieved if components were only removed when significant corrosion damage had actually occurred. As part of an effort to find a useful method for online corrosion monitoring, previous experiments had indicated that the electrochemical frequency modulation technique appeared to be sensitive to the onset of SPC. However, these experiments were conducted using specimens that had been heat treated to enhance susceptibility. Additional experiments are being conducted in an attempt to determine the sensitivity of this technique to the onset of SPC in specimens with a range of heat treatments, including specimens with microstructures similar to those found in service. At the conclusion of the electrochemical tests, specimens will be sectioned and inspected for evidence of selective attack.