The Corrosion of Copper-Nickel Alloys 706 and 715 in Flowing Sea Water. I—Effect of Oxygen Available to Purchase

The corrosion of 90:10 Cu:Ni and 70:30 Cu:Ni alloys in flowing seawater (1.62 m/s) has been studied as a function of oxygen concentration using the linear polarization, ac impedance, and potential step methods for measuring the polarization resistance. The high nickel alloy is found to be more corrosion resistant than the 90:10 Cu:Ni alloy under the conditions employed, provided that [O₂] ⩽6.60 mg/L. In oxygen saturated seawater, the superior behavior of the 70:30 Cu:Ni alloy is no longer observed. The loss in corrosion resistance of the 70:30 Cu:Ni alloy is correlated with a shift in the corrosion potential, to a value more noble than the “break-away potential” (defined here as the potential at which a sudden increase in anodic current occurs on sweeping the potential in the active to noble directions).