Electrochemical noise analysis of the hot corrosion of TP347H stainless steel: Effect of temperature and coal ash thickness

Hot corrosion detection has long been a challenge, and in-situ analysis of high-temperature electrochemical kinetics and corrosion processes is continuously evolving. Herein, electrochemical noise (EN) was employed as a reliable method to study the hot corrosion of TP347H stainless steel systematically at various temperatures (650 °C, 700 °C, and 750 °C) and coal ash thicknesses (3 mm and 6 mm). Other corrosion detection techniques were also used such as weight loss, open circuit potential (OCP) and potentiodynamic polarization (PDP) in addition to characterization techniques such as scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD). Results revealed that the trend of corrosion rate is 650 ° C < 750 ° C < 700 °C. The reduction in corrosion rate at 750 °C was attributed to the decomposition of surface iron sulfate and the formation of a new protective iron oxide layer. Additionally, increased thickness of the molten salt layer was found to accelerate the corrosion rate by enhancing the solubility of pyrosulfate salts. Also, the corrosion mechanism was further elucidated with the aid of SEM and XRD characterization. Detailed analysis of electrochemical noise using shot noise theory, and the Hilbert-Huang Transform (HHT) clarified the relationships between corrosion mechanism and electrochemical signals, by evaluating charge transfer, pit initiation rate, growth rate, and the frequency and amplitude of events. These findings also demonstrate the effectiveness of advanced analysis of electrochemical noise data for studying hot corrosion.