Research on the Mechanism and Detection Method of Intergranular Corrosion of AISI 304 Stainless Steel by Electrochemical Techniques in Heat Exchanger Equipment

Intergranular corrosion (IGC) is one of the common pernicious forms of corrosion in heat exchanger equipment in the refinery. Electrochemical measurements including the etching technology, the double loop electrochemical potentiokinetic reactivation (DL-EPR) and the electrochemical impedance spectroscopy (EIS) were taken to study the IGC evolutions and its detection method of the liner 304 stainless steel. The result reveals that the IGC induced by improper operations on-site emerges rapidly within 15 min at 700 °C due to the chromium carbide precipitates at the grain boundaries. Compared with the DL-EPR test and etching technology, EIS was found to be more valid in characterizing the relationships between the IGC and the microstructure evolutions because of its nondestructive property. Therefore, the checkout equipment based on EIS is proposed to assess the degree of sensitization (DOS) toward IGC, which can examine the tiny cracks (DOS < 5%) and monitor the IGC in time.