Theoretical model and its verification for the effect of sand concentration on the critical flow velocity for erosion-corrosion of 304 stainless steel in 3.5 wt.% NaCl solution

A theoretical model based on fluid dynamics and mechanical analyses was proposed to explain the relationship between the critical flow velocity (CFV) and sand concentration which indicated that the CFV followed a power law of C-m(-0.5), i.e. CFV varied with C-m as a power function with exponent of -0.5. Potentiostatic polarisation measurements were performed on 304 stainless steel during the erosion-corrosion process to validate the model. The erosion-corrosion tests were conducted at various flow velocities between 0 and 17 m s(-1) and four silica sand concentrations of 2-5 wt.% under the impingement of sand-containing NaCl solution at an impact angle of 90 degrees. It was observed that the anodic current density under a controlled potential increased significantly when the flow velocity was above a critical value. The CFV values of 304 stainless steel under impingement by NaCl solution containing 2-5 wt.% sand are 14, 11(1), 9 and 8 m s(-1), respectively. The experimental results showed that the CFV did follow a power law of sand concentration, while the exponent deviated from the theoretical predicted result. The deviation was attributed to the difference between the actual impact velocity and the inlet flow velocity according to the calculated results by the computational fluid dynamics (CFD) model. And the corrected CFV followed a power law of C-m(-0.495) which was in consistence with the predicted result (v(c)alpha C-m(-0.5)).