In seawater, higher strength nickel-copper alloys are used as alternatives to copper alloys. These can be susceptible to chloride stress corrosion cracking and hydrogen embrittlement in conditions where cathodic protection is utilized. Copper-Nickel-Tin alloys (CuNiSn) show low corrosion rates in the free and coupled conditions. Resistance to hydrogen embrittlement is demonstrated.
04298 2004 CP
John O. Ratka, Brush Wellman Inc.; Manuel N. Maligas, FMC Technologies
Copper–based alloys are commonly used in numerous seawater applications mainly because of resistance to biofouling and low corrosion rates. The low strength of most copper alloys limits their use in structural applications and components. Higher strength alloys used in seawater, such as nickel-copper are used as alternatives to copper alloys, however, these alloys can be susceptible to chloride stress corrosion cracking and, at times, hydrogen embrittlement in conditions where cathodic protection is utilized. A relatively young family of age hardenable high strength ternary CuNiSn alloys deliver combinations of high strength and corrosion resistance in seawater and chloride environments in both cast and wrought conditions. This paper documents basic corrosion behavior previously unavailable for a series of high strength CuNiSn alloys. Slow strain rate testing of this alloy family was conducted under freely corroding and under cathodic protection conditions. Galvanic couples, with various area ratios, were evaluated in conjunction with regularly used ferrous and non-ferrous corrosion-resistant alloys. Low corrosion rates in the free and coupled conditions are observed, and resistance to hydrogen embrittlement is demonstrated. The results suggest that the CuNiSn alloys can function in high performance seawater valves and fastener applications.
Keywords: Copper based alloys, biofouling, corrosion rates, nickel-copper, cathodic protection, hydrogen embrittlement, slow strain test, corrosion resistant alloys, CuNiSn