Localized corrosion tests were performed on a series of stainless steel and nickel-base alloys in a reverse osmosis plant utilizing seawater. Open circuit potential (OCP) measurements show some ennoblement and some occasional fluctuation in the behavior of the alloys, which can be related to nucleation and repassivation of pits and/or crevices on their surfaces. Analysis of the electrochemical behavior and microscopic observations show that UNS S31603 and UNS S31703 susceptible to pitting and crevice corrosion, whereas the remaining studied alloys exhibited good resistance.