A Comparative Study on Corrosion Behaviors of 15CrMo in Saline (Na2SO4) Gas Phase and Liquid Phase at 350°C

The differences between the corrosion behaviors of 15CrMo in saline (Na2SO4) saturated steam and saline saturated water are clarified in this study. The corroded samples were analyzed by scanning electron microscope/energy dispersive spectrum (SEM/EDS), x-ray diffraction, and x-ray photoelectron spectroscopy. The results indicate that the destruction of cementite (Fe3C) could be intensified in the saline gas phase. In saline saturated steam (gas phase), the corroded surface is mainly covered by Fe3O4, which is in form of irregular particles. In addition,, dissolved SO in the steam (gas phase) is reduced to S2-. In the gas-phase corrosion of 15CrMo, insoluble sulfide occurs. In saturated saline water (liquid phase), smaller particles are distributed on the surface. The corrosion products in liquid-phase corrosion consists of Fe3O4, Fe2O3, and Fe. The surface of 15CrMo in the saturated saline gas phase is corroded more severely than in the liquid phase in the fixed conditions. The crystal Fe3O4 is well formed in the liquid/gas phases. The crystallinities of Fe3O4 are 99.50% (gas-phase corrosion) and 99.87% (liquid-phase corrosion).