ELECTROCHEMICAL BEHAVIOUR OF COPPER-NICKEL ALLOY CUNI 90/10 IN CHLORINATED SEAWATER UNDER STAGNATING CONDITIONS

摘要

The copper-nickel alloy CuNi 90/10 has been extensively used on different marine engineering structures. Its main application is piping for seawater handling and heat exchangers. Regardless of the macro fouling resistance of the material, seawater is often chlorinated. As there is only limited information available about the effect of chlorination on the corrosion rate of copper-nickel, a systematic approach is required to understand the effect of free chlorine on its corrosion behavior. The aim of the first part of this project has been the characterization of the electrochemical behavior of CuNi 90/10 in chlorinated seawater under stagnating conditions at room temperature. The results were obtained in synthetic seawater containing up to 5 ppm free chlorine using fresh and pre-exposed samples. Testing involved free corrosion potential and polarization resistance measurements, cathodic and anodic polarization as well as gravimetric and metallographic examinations. The data obtained did not reveal a distinct relationship between corrosion behavior and the free chlorine concentration. Instead, the corrosion rate was found to decrease with increasing formation of oxide layers. This fact underlines a clear advantage of CuNi 90/10 versus high alloy materials in applications where the presence of chlorine is often combined with high seawater temperatures. The data obtained is being used as the basis for a second part of the project, which compares chlorination under erosive conditions with previously reported data. This will be used to validate current practical service recommendations.