Abstract: A method for protecting cooling water systems from corrosion is disclosed which monitors the hydrocarbon concentration in a cooling fluid flow and activates protective procedures upon detection of a predetermined concentration. According to the method, a fluid flow of cooling water from a cooling tower is directed through an upstream gate valve before entering a heat exchange apparatus where heat from an industrial process fluid flow is transferred to the cooling fluid flow. The hydrocarbon concentration of the heated cooling fluid flow is monitored as it is directed out of the heat exchange apparatus for return to a cooling tower. However, if a concentration of hydrocarbons is detected in the fluid flow which indicates possible process fluid leakage, upstream and downstream cooling fluid gate valves as well as a process fluid gate valve are automatically closed.