Corrosion behaviour of cupronickel 90/10 condenser tubes in thermal desalination plant MED exposed to synthetic seawater at different temperature

摘要

Cu-Ni 90/10 alloys used in seawater desalination shell-heat exchangers and condensers exhibit a good resistance toward corrosion. This resistance results from the formation of a protective oxide film that forms naturally and quickly when exposed to seawater. Unfortunately, some Cupronickel tubes suffer from severe corrosion due to the combination of heating and evaporating process of seawater. The aim of this study was to evaluate the temperature effect on corrosion behaviour of 90/10 Cu-Ni from 20°C to 80°C by electrochemical techniques in artificial seawater under stirring conditions. The corroded surfaces were then analysed by optical microscopy, SEM and m-Raman Spectroscopy. OCP, Rp and EIS measurements show that the alloy exhibit a resistance toward corrosion after immersion in synthetic seawater which increase with increasing temperature up to T< 60°C. The composition of the film formed on the tube immersed in seawater after 48h of immersion has revealed an enrichment of the oxide film in Ni. m-Raman spectroscopy shows that whatever the temperature, the oxide film is composed of Cu oxide and Ni oxide covered by a calcareous layer. At 80°C, OCP decreases in the cathodic direction and Rp is reduced. This result was attributed to a lower dissolved O_2 and then to a less resistive oxide film that gives rise to a higher corrosion rate.