Influence of flow velocity on electrochemical corrosion resistance of carbon steel and 316 L stainless steels in 3.5 % sodium chloride solution

A newly designed rotating corrosion experimental setup was constructed to study the electrochemical corrosion resistance of 20# carbon steel and 316 L stainless steels in 3.5 % NaCl corrosive solution combining electrochemical measurements and surface analysis techniques. The effect of flow velocity on the electrochemical corrosion resistance of steel substrates in corrosive solution was investigated using a combination of electrochemical testing and computational fluid dynamics (CFD) simulation. The electrochemical corrosion tests, including open circuit potential, electrochemical impedance spectroscopy, and polarization measurements, were conducted to assess the corrosion behavior of the materials under different flow velocities. The results revealed that the corrosion products on 20# carbon steel formed a loose and porous structure, whereas the surface of 316 L stainless steel remained smooth, exhibiting significantly good corrosion resistance. Moreover, the corrosion rates of 20# carbon steel and 316 L stainless steel exhibit a nonlinear dependence on flow velocity, with a distinct critical flow velocity identified. Specifically, the critical flow velocities for 20# carbon steel and 316 L stainless steel were 2 m/s and 1.5–2 m/s. Prior to reaching the critical flow velocity, the overall corrosion rate decreased as flow velocity increased. However, beyond this threshold, the corrosion rate increased due to the localized breakdown of the protective corrosion product film. In addition, CFD simulations were conducted to investigate the hydrodynamic factors, and the results showed that the magnitude of fluid-induced shear stress did not exhibit a clear positive correlation with the corrosion rate.