How to Calculate Corrosion Rate from Tafel Plot

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Tafel Plot Corrosion Rate Calculator

Calculate Corrosion Rate (CR) from Electrochemical Polarization Data

μA/cm²
Obtained from the intersection of Tafel slopes.
g/eq
Atomic weight / Number of electrons transferred.
g/cm³
Density of the metal/alloy being tested.

Calculated Results

Rate (mm/year)

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Rate (mils/year – mpy)

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Rate (μm/year)

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How to Calculate Corrosion Rate from a Tafel Plot

The Tafel extrapolation method is a powerful electrochemical technique used to determine the corrosion rate of a metal in a specific environment. By polarizing the metal electrode and measuring the resulting current, we can determine the corrosion current density (icorr).

Step 1: Perform Potentiodynamic Polarization

Scan the potential of the working electrode from roughly -250 mV to +250 mV relative to the Open Circuit Potential (OCP). Plot the results on a Semi-Log graph, where the Y-axis is the Potential (E) and the X-axis is the logarithm of the Current Density (log i).

Step 2: Extrapolate Tafel Regions

Identify the linear portions of the anodic and cathodic branches. These linear regions usually occur at least 50-100 mV away from the corrosion potential (Ecorr). Draw straight lines through these regions. The point where these two lines intersect defines the values of Ecorr and icorr.

Step 3: Apply Faraday's Law

Once you have icorr, use the following formula to calculate the Corrosion Rate (CR) in mm per year:

CR (mm/y) = (K × icorr × EW) / ρ
  • K: Constant 3272 (for mm/y when icorr is in A/cm²) or 0.00327 (when icorr is in μA/cm²).
  • icorr: Corrosion current density.
  • EW: Equivalent Weight (Atomic weight of metal / number of electrons lost).
  • ρ: Density of the material in g/cm³.

Common Material Properties Table

Material Density (ρ) Eq. Weight (EW)
Carbon Steel (Iron base) 7.87 g/cm³ 27.92 g/eq
Aluminum (1100) 2.71 g/cm³ 8.99 g/eq
Copper 8.96 g/cm³ 31.77 g/eq
Stainless Steel 304 7.94 g/cm³ 25.50 g/eq
Pro Tip: To get accurate icorr values, ensure the Tafel regions extend over at least one decade of current density. Avoid regions where diffusion limitations (concentration polarization) might distort the linear relationship.
function calculateCorrosion() { var icorr = parseFloat(document.getElementById("corrosionCurrent").value); var ew = parseFloat(document.getElementById("equivWeight").value); var rho = parseFloat(document.getElementById("materialDensity").value); if (isNaN(icorr) || isNaN(ew) || isNaN(rho) || rho <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // K constant for mm/y using microAmps/cm2 is 0.00327 // Formula: CR = (0.00327 * icorr * EW) / rho var mmy = (0.00327 * icorr * ew) / rho; // Conversion to MPY (Mils Per Year) // 1 mm = 39.37 mils var mpy = mmy * 39.3701; // Conversion to Micrometers per year var umy = mmy * 1000; document.getElementById("resMMY").innerHTML = mmy.toFixed(4); document.getElementById("resMPY").innerHTML = mpy.toFixed(4); document.getElementById("resUMY").innerHTML = umy.toFixed(2); document.getElementById("resultsArea").style.display = "block"; }

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