[en] Polarization curves and mass losses of SAF3207 hyper-duplex stainless steel under various conditions were measured. The damaged surfaces after erosion–corrosion tests were characterized by scanning electron microscopy. The results showed that an increase in flow velocity could enhance the electrochemical corrosion and consequently decrease the passivation properties of the steel. The erosion–corrosion damage of the samples increased substantially when the flow velocity exceeded the critical value of 4 m·s⁻¹. The mass loss rate increased as the sand content increased, reaching a maximum at 7wt% sand content, corresponding to the most severe electrochemical corrosion damage. When the sand content was increased further, however, the mass loss rate decreased and then tended stable. The mass loss was divided into incubation, sustained, and stationary periods, with a maximum mass loss rate of 12.97 g·h⁻¹·m⁻² after an erosion period of 2.5 h. The erosion–corrosion mechanism was investigated in detail.