A Study to Determine the Mechanisms of Corrosion of Copper-Nickel Alloys in Sulfide-Polluted Seawater

Abstract : The main objective of this research was to determine the role of dissolved sulfide pollutants on the seawater corrosion of two copper nickel alloys--90:10 Cu:Ni (CA 706) and 70:30 Cu:Ni (CA 715). Electrochemical techniques were used to monitor corrosion rates in rotating cylinder experiments and in flow loop experiments. The effects of flow (velocity) and the composition of the seawater environment were considered. The highlights of this work are as follows: (1) Electrochemical methods are suitable for monitoring the corrosion rate of copper-nickel alloys in seawater if certain precautions are taken. (2) The presence of sulfide or one of several sulfide oxidation products turns noncorrosive deaerated seawater into a comparatively corrosive environment. (3) Sulfide-polluted deaerated seawater is less corrosive than unpolluted aerated seawater at Reynolds numbers up to 74,000 (velocities up to 5 m/s). (4) When the velocity of aerated seawater is increased from 2 m/s to 3 m/s (Reynolds number from 30,000 to 44,000), 70:30 Cu:Ni undergoes a transition from fairly uniform mild corrosion to accelerated localized corrosion. This breakaway corrosion phenomenon is interpreted in terms of a 'breakaway potential.' (Author)