Effects of ferrous ions released from sacrificial steel anodes on corrosion of copper-nickel alloys in sulphide polluted sea water

Abstract

Specimens of Naval brass and 70–30 and 90–10 copper-nickel were monitored using the polarisation resistance method during lengthy exposure to flowing sea water that was intermittently contaminated with sulphides. Exposure of the 90–10 or 70–30 alloys to sulphides delayed or prevented the development of a protective film during subsequent exposure to clean sea water. Until such afUm developed, the corrosion rate of 70–30 alloy was twice that of90–10 alloy. However, even after initial exposure to sulphides, the 70–30 alloy could eventually passivate in clean sea water. Some specimens were exposed to sea water also containing ferrous ions at concentrations of 1 and 0·05 ppm. These additions reduced the corrosion rates of both 90–10 and 70–30 alloys, but not Naval brass at 0·05 ppm. The continuous addition of ferrous ions at 0·05 ppm caused the rapid development of a protective film on 70–30 alloy that was not affected by subsequent exposure to sulphides.