The Influence of Flow Rate on the Erosion–Corrosion Behavior of 304 Stainless Steel in Sulfur-Containing and Sand-Containing Sodium Aluminate Solutions

Regarding the erosion–corrosion problem of 304 stainless steel, which is commonly used in the production of alumina, in high-temperature, high-pressure, and strongly alkaline aluminum ammonium solutions, a detailed study was conducted on the erosion–corrosion behavior and damage mechanism of 304 stainless steel in a sodium aluminate solution with varying S2− concentrations at 65 °C and pH = 14 under the influence of key factors such as erosion speed. This study quantitatively revealed, for the first time, the flow rate threshold effect (critical point at 2 m/s) of 304 stainless steel during scouring corrosion in a strongly alkaline aluminum ammonium solution, identified its peak weight loss rate (1.892 × 10−3 g/m2·d), and innovatively elucidated the mechanism reversal phenomenon: below the threshold, passive film destruction and corrosion synergistically dominate, while above the threshold, high oxygen mass transfer promotes film regeneration. These findings provide a critical theoretical basis for precise flow rate control and equipment life prediction in alumina production processes.