Prediction of Corrosion Rate of Pipes and Tubes using Rotating Electrode
Kozo Denpo, Hiroyuki Ogawa
The effects of fluid flow on the corrosion rate of pipes and tubes were studied with rotating disk electrode and a prediction method for corrosion rate was proposed. Polarization curves in both N2-purged and CO2-saturated NaCl solution were depolarized with the increase of angular velocity showing the increase of limiting current density and corrosion current density. The limiting current density increased linearly as a function of the square root of angular velocity which shows the rate determining process is the diffusion of H+ ion to the electrode surface. Another possibility contributing the rate determining process is the CO2 hydration reaction to H2CO3. The corrosion current density also increased as a function of square root of rotating velocity following the theoretical solution. Using the similarity solutions obtained for mass transfer with pipe flow and rotating disk electrode, the rotating velocity was converted to the equivalent velocity in pipe. On that basis the corrosion rate of pipe was equal to the corrosion rate of the rotating disk electrode. The corrosion rate of rotating disk electrode obtained by the electrochemical method was used to predict the corrosion rate of the pipe at the equivalent velocity.