Erosion and Passivation of Borated 254 SMO Stainless Steel in Simulated Flue Gas Desulfurization Solution

Grain boundary erosion and passivation of 254 SMO stainless steel with and without boron were investigated in a medium of simulated flue gas desulfurization (FGD) solution. Electrochemical measurements were carried out using potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky analysis to determine the significance of boron addition at different temperatures. After potentiodynamic polarization, microstructures and grain boundary erosion were evaluated at 60 °C using scanning electron microscopy (SEM). It was found that the dissolution/erosion of grain boundary is much lower when boron is added. Energy-dispersive X-ray spectroscopy was carried out after SEM to determine the reason of grain boundary erosion of nonborated 254 SMO and compared the passive regions of polarization tests at 60 °C. Experimental results show that the addition of boron significantly hindered the corrosion rate, pits initiation sites, and passive film dissolution. Deconvolution of peaks obtained from X-ray photoelectron spectroscopy (XPS) and their depth profiles after 60 °C passivation confirmed that boron not only stopped the corrosion behavior but also increased the stability and repassivation ability of passive film.