Relationships Between Corrosion and Fouling of Copper-Nickel Alloys in Sea Water

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Abstract
Exposure of a series of copper‐nickel alloys in natural sea water, under conditions which permitted detailed observations of the relationships between fouling and corrosion, disclosed that: 1. In order for fouling to be prevented, copper must be released in corrosion products at a rate greater than 4.5 to 7 mg./dm.2/day. 2. The division between practically no fouling and appreciable fouling occurred between 30% and 40% nickel in copper‐nickel alloys containing no added iron. 3. The fouling organisms, Balanus eburneus and Bugula neritina, accelerated localized corrosion, especially after their death. This effect was greatest with the alloys that fouled earliest and most. 4. Acceleration of corrosion by fouling organisms began in the early stages of fouling and was quite noticeable within 11 days after fouling had appeared. 5. Neither Serpula nor Algae showed any tendency to accelerate corrosion. 6. Alloys that did not foul showed decreases in corrosion rates as the period of exposure was prolonged. The decrease was most evident with the 30% nickel alloy. 7. Alloys that fouled showed increases in corrosion rates when fouling developed as the period of exposure was prolonged. 8. On account of the complexity of factors influencing corrosion under these conditions of exposure, tests of this sort must be considered of doubtful value in establishing passivity limits in alloy systems. 9. The results suggested that the sloughing off of solid corrosion products must be considered, along with toxicity, as a major factor in determining the fouling characteristics of metals and alloys in sea water.

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