Calculate the corrosion current density for a steel pipe of diameter 10 cm and length 20 m, which is exposed to a 0.1 M HCl solution. The corrosion potential of steel in the given environment is -0.5 V (SHE), the Tafel slope is 0.12 V/decade, and the temperature is 25°C. Consider the density of steel to be 7.86 g/cm³ and the flow rate of the solution to be 5 L/min.

Question

Calculate the corrosion current density for a steel pipe of diameter 10 cm and length 20 m, which is exposed to a 0.1 M HCl solution. The corrosion potential of steel in the given environment is -0.5 V (SHE), the Tafel slope is 0.12 V/decade, and the temperature is 25°C. Consider the density of steel to be 7.86 g/cm³ and t

Answer 1

To calculate the corrosion current density, we need to determine the exchange current density  i0  and the corrosion current  icorr . We can use the Butler-Volmer equation to find the corrosion current density  jcorr .Butler-Volmer equation:j = j0 *  exp  1 -   * n * F *  E - Ecorr  /  R * T   - exp - * n * F *  E - Ecorr  /  R * T   where:j = current density  A/cm j0 = exchange current density  A/cm  = charge transfer coefficient  dimensionless, typically 0.5 for a one-electron transfer process n = number of electrons transferred in the reaction  for steel, n = 2 F = Faraday's constant  96485 C/mol E = applied potential  V Ecorr = corrosion potential  -0.5 V R = gas constant  8.314 J/molK T = temperature  298 K First, we need to find the exchange current density  j0 . We can use the Tafel equation to find j0:Tafel equation:E = Ecorr +  b * log10 j / j0  where:b = Tafel slope  0.12 V/decade Rearranging the Tafel equation to solve for j0:j0 = j / 10^ E - Ecorr  / b Since we don't have the value of j, we can't directly calculate j0. However, we can use the Stern-Geary equation to find the corrosion current  icorr  and then use the Tafel equation to find j0:Stern-Geary equation:icorr = j0 *  exp - * n * F * Ecorr /  R * T   - exp  1 -   * n * F * Ecorr /  R * T   Rearranging the Stern-Geary equation to solve for j0:j0 = icorr /  exp - * n * F * Ecorr /  R * T   - exp  1 -   * n * F * Ecorr /  R * T   Now we can plug in the values and calculate j0:j0 = icorr /  exp -0.5 * 2 * 96485 * -0.5 /  8.314 * 298   - exp  1 - 0.5  * 2 * 96485 * -0.5 /  8.314 * 298   Unfortunately, we don't have the value of icorr. In order to find the corrosion current density, we need more information about the system, such as the polarization resistance or the corrosion rate. Without this information, we cannot calculate the corrosion current density.