Sulfide Induced Corrosion of Copper Nickel Alloys

The susceptibility of Cu-Ni alloys to accelerated corrosion in sea water containing low sulfide concentrations has been investigated. Test alloys included wrought 90/10 Cu-Ni, 70/30 Cu-Ni and Ni-Cu, plus cast 70/30 Cu-Ni. Sheet type specimen exposures were performed in fresh flowing sea water at a test velocity of 2.4 m/s (8 ft/s), and simultaneous polarization resistance cell exposures were conducted at a test velocity of 1.2 m/s (4 ft/s). Sulfide concentrations included 0.01, 0.05, and 0.2 ppm from addition of Na2S to flowing sea water. The test sequence included continuous sulfide exposures ranging from 1 to 15 days, followed by 60 days exposure in natural sea water. Gravimetric corrosion rates, depth of attack, corrosion potentials, and instantaneous corrosion rate data were developed. Results showed that wrought 90/10 Cu-Ni was susceptible to accelerated attack in sea water containing 0.01 ppm sulfides and is attacked vigorously after exposure to 0.2 ppm sulfides in sea water. Wrought 70/30 Cu-Ni is similarly susceptible to sulfide induced pitting, but appears to require higher sulfide concentration to trigger attack. Cast 70/30 Cu-Ni and Ni-Cu are susceptible to accelerated corrosion in sulfide modified sea water, but modes of attack differ from wrought 90/10 and 70/30 Cu-Ni. Interaction of exposure (or system operating) variables is seen as a key factor in assessing susceptibility of Cu-Ni alloys to sulfide induced corrosion.