Copper-based alloy tubes (i.e. Cu-Ni) are extensively used in desalination plants. This is in order to complete the heating and evaporating process for the seawater and to obtain distillate water that can be used in the steam generation plant and as drinking water. A number of these tubes were found to suffer from severe localized corrosion at 6 o'clock position (corrosion throughout the pipe wall thickness). Several samples from the failed tubes were subjected to metallographic examination and electrochemical test in the simulated working environment (i.e. chloride content, temp. non evacuated system) in order to establish the main cause of corrosion and failure of the tubes.