Chiang Mai Journal of Science

In a combined cycle power plant, a separated-type condenser is an important component that uses natural water from nearby river to sustain the operation. Type 304 stainless steel is used as tubes in a heat exchanger. Type 304 stainless steel is known to be susceptible to pitting corrosion when certain amount of chloride is present. Saltwater intrusion is a primary concern, in this particular case, because it contaminates freshwater with high concentration of chloride. The monitoring of chloride concentration in the nearby river showed that chloride concentration spiked up to 4500 ppm particularly in dry season. The goal of this study is to understand pitting corrosion behavior of type 304 stainless steel in laminar flow conditions. In order to simulate the actual working environment of type 304 stainless steel tubes in this application, flow velocity, chloride concentration, and temperature are varied. Flow velocity is simulated by a magnetic stirrer. Evaluation of localized corrosion behavior is conducted using potentiodynamic and electrochemical impedance spectroscopy (EIS). Visual observation is performed to characterize the samples after corrosion tests. Computational simulation illustrates the flow phenomena inside the pit. Results show that the aggressiveness of chloride is diminished by a washout effect. Pit density is reduced with increasing flow velocity. Maximum pit depth under hydrodynamic condition is reduced compared with ones under stagnant condition. Keywords: 304 stainless steel , pitting corrosion, flow-induced corrosion, EIS.