CORROSION OF CU-NI ALLOYS IN SULFIDE-POLLUTED SEAWATER

A study of the corrosion of copper-nickel (Cu-Ni) alloys showed hydrod ynamic conditions increased the corrosion rate (l(corr)) significantly by reducing the sulfide concentration polarization. Pre-exposure to o xidation products of dissolved sulfide and elemental sulfur (S) increa sed l(corr) of the alloys in seawater significantly. Pre-exposure to n itrite and chromate decreased l(corr) by almost 2 orders of magnitude for alloys of 90% Cu-10% Ni and 70% Cu-30% Ni (UNS C70600 and UNS C715 00, respectively) However, cyclic polarization curves for both alloys pre-exposed to chromate and nitrite showed the passivators caused seve re localized corrosion for the 70% Cu-30% Ni alloy only by transition from the active to passive state. The corrosion mechanism of the 90% C u-10% Ni alloy differed from that of the 70% Cu-30% Ni al!oy in quiesc ent sulfide-polluted seawater. A four-part corrosion mechanism was pro posed. The rate of sulfide ion diffusion to the alloy-solution interfa ce always was the rate determining step for corrosion of the alloy of higher Ni content, whereas different kinetics of the reaction determin ed l(corr) of the second alloy.