Determination of the critical flow velocities for erosion–corrosion of passive materials under impingement by NaCl solution containing sand

• Three different methods were used to study critical flow velocity (CFV).
• The CFV values defined via the three methods agreed well with one another.
• The CFV values decreased with increasing sand content for the two test materials.
• The theoretical meanings and practical significance of the CFV were discussed.

Transition from passivation to erosion–corrosion at the critical flow velocity (CFV) is of interest for corrosion engineers. This transition phenomenon on 304 stainless steel and a Fe-based amorphous coating was investigated under impingement by sand-containing NaCl solution. Mass loss measurement, open-circuit potential monitoring and potentiostatic test were employed to determine the CFV. The CFV values defined via the three approaches are consistent, about 10 m/s for 304 stainless steel and 15 m/s for the coating. The CFV decreases with increasing the sand concentration. It may serve as an effective tool for evaluating the erosion–corrosion resistance of passive materials.