The Impact of pH Value on Corrosion Behavior of 316L, 2507 and TA2 Alloys

The corrosion resistance of metallic materials is closely related to their service environment. In ammonia-based desulfurization post-treatment systems, 316L stainless steel, 2507 duplex stainless steel, and TA2 commercially pure titanium are widely used as candidate materials for key components such as desulfurization heat exchangers. In this study, the pitting corrosion behavior of 316L, 2507, and TA2 was investigated in simulated ammonia desulfurization post-treatment solutions with different pH. The results show that increasing solution acidity leads to a decrease in the capacitive arc radius and polarization resistance, while the donor concentration and pitting susceptibility of the three materials increase. Under the same pH condition, TA2 exhibits the highest stability and corrosion resistance, followed by 2507, whereas 316L shows the poorest corrosion resistance. The composition of the TA2 passivation film (TiO2) does not change as the pH of the simulated solution is modified. With increasing solution acidity, the relative XPS peak-area fraction of TiO2 in TA2 increases, indicating that TiO2 remains the dominant component of the passive film. In contrast, the relative contents of Cr- and Mo-containing oxides/hydroxides in 316L and 2507 decrease, and MoO3 is replaced by MoO2 under acidic conditions. These changes suggest weakened passive-film stability and reduced protection of the substrate.