Abstract: By observing the corrosive appearance of the disabled exchange-heater,analyzing the chemical component of corrosion product and water quality for the electric desalter,and investigating the technical conditions of the exchange-heater,the corrosion reason of the exchange-heater used for electric desalter in a delay cooking unit.The results show that the failure of the outer tube surface of exchange-heater is induced by the under-deposit corrosion resulting from gathering of calcium,barium and bedload in fresh water on the tube surface.The failure of the exchange-heater tube inner surface is caused by electrochemical corrosion in the desalting water having lower pH value.