Research on Corrosion Behavior of 20 Steel in Simulated High Chloride Desulfurization Wastewater

Corrosion of pipelines by flue gas desulfurization (FGD) wastewater compromises the normal operation of the desulfurization tower, and corrosion under high-chloride conditions in particular severely damages the tower’s internal structure. To further elucidate the corrosion mechanism at elevated Cl− concentrations, the corrosion behavior of 20 steel exposed to high-chloride FGD wastewater at different Cl− concentrations was investigated through weight-loss measurements, electrochemical tests, immersion corrosion experiments, composition analysis, and microscopic morphology characterization. The results revealed that higher Cl− concentrations corresponded to lower corrosion rates: the corrosion rate reached 0.1964 mm/y in the absence of Cl−, but decreased to 0.1537 mm/y at a Cl− concentration of 100,000 mg/L. XPS analysis showed that as the Cl− concentration increased, the corrosion film gradually transformed from porous FeOOH into dense Fe3O4. Localized pitting analysis indicated a positive correlation between Cl− concentration and pitting susceptibility. At Cl− concentrations of 0 and 100,000 mg/L, the corrosion current density decreased from 32.44 μA/cm2 to 6.43 μA/cm2 after 72 h, decreasing by a factor of approximately 5.05. This behavior is attributed to the fact that Cl− increases solution conductivity in high-chloride environments, thereby promoting the formation rate of the corrosion film. Additionally, high Cl− levels reduce dissolved oxygen in the solution, causing the corrosion film to progressively react and form denser Fe3O4. Nevertheless, the high penetrability of Cl− continues to aggravate pitting corrosion of 20 steel.