Failure of condenser tubes due to non-condensable gases is a common problem of MSF distillers and have been reported by many authors. However, information is lacking in ascertaining the actual cause of corrosion on the basis of chemistry of corrosion products from the failed tubes. In this paper the causes of 90/10 Cu-Ni alloy condenser tubes of MSF desalination plant have been discussed. The cause of the failure has been investigated by systematic and, detailed inspection of the evaporator in general and condenser tubes in particular. The corrosion products were analyzed using EDAX and EPMA techniques. It was found that the failure of condenser tubes appears to be mainly due to dissolution of the CO2 along with some S containing compounds in condensate water vapor. Some operational modifications in the vent line have been recommended to avoid the dissolution of non-condensable gases in condensate water.