CuNi Alloys in Chlorinated Substitute Ocean Water--Effect of Sulfide in Surface Preconditioning with Substitute Ocean Water

摘要

Six weeks exposure tests were run with CuNi 70 30 (C71500) and CuNi 90 10 (70600) tubes in a flow loop with artificial ASTM seawater (pH 8.2; flow rate 0.5 m/s) at room temperature and 40°C in the absence and presence of 1 ppm hydrogen sulfide. The effect of hypochlorite addition (0.5; 1.0; 3.0 ppm; sensor controlled) was investigated on tube surfaces i) in the as-received surface condition, ii) after conditioning with additive-free artificial seawater and iii) after conditioning with artificial seawater containing 1 ppm bisulfide. The conditioning was performed for 6 weeks at room temperature under access of air. On a non-conditioned as-received tube surface the presence of hypochlorite increases the mass loss rate. The effect increases with the hypochlorite concentration and decreases with increasing temperature (40°C). Pre-conditioning of the inner tube surface with additive-free artificial seawater is beneficial to improve performance in the presence of hypochlorite. The presence of bisulfide in the flowing seawater significantly decreases the corrosion resistance of both types of CuNi alloys in the as-received surface condition, as well after 6 weeks conditioning with additive-free and bisulfide containing seawater.