Recent changes in construction techniques and operational practice have resulted in a number of failures of copper-nickel components in sea water systems. These failures include erosion corrosion of welded 90/10 copper-nickel pipe, erosion corrosion of 90/10 copper-nickel heat exchanger tubes, “hot-spot” corrosion of 70130 copper-nickel tubes and denickelification of 70130 copper-nickel tubes. Case histories describing examples of each of these problems are presented. Factors contributing to these failures, such as welds protruding into the flow stream, tight bends, contamination by marine organisms, unusual flow patterns and exposure to sulfide-polluted, stagnant sea water, are discussed. Methods to prevent or reduce the future occurrence of these problems are also presented. Keywords: corrosion, sea water, copper-nickel alloys, erosion, impingement, denickelification, sulfide-induced corrosion.