How to Calculate Corrosion Rate from Weight Loss

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Corrosion Rate Calculator (Weight Loss Method)

mils per year (mpy) millimeters per year (mm/y)

Calculation Result:

function calculateCorrosionRate() { var W = parseFloat(document.getElementById("weightLoss").value); var A = parseFloat(document.getElementById("surfaceArea").value); var T = parseFloat(document.getElementById("timeHours").value); var D = parseFloat(document.getElementById("materialDensity").value); var unit = document.getElementById("unitType").value; var resultBox = document.getElementById("corrosionResult"); var resultDisplay = document.getElementById("resultDisplay"); var resultInterpretation = document.getElementById("resultInterpretation"); if (isNaN(W) || isNaN(A) || isNaN(T) || isNaN(D) || A <= 0 || T <= 0 || D <= 0) { alert("Please enter valid positive numbers for all fields."); return; } var K; var unitLabel; if (unit === "mpy") { // K for mpy = 3.45 x 10^6 K = 3450000; unitLabel = " mpy (mils per year)"; } else { // K for mm/y = 8.76 x 10^4 K = 87600; unitLabel = " mm/y (millimeters per year)"; } var corrosionRate = (K * W) / (A * T * D); resultDisplay.innerHTML = corrosionRate.toFixed(4) + unitLabel; resultBox.style.display = "block"; var interpretation = ""; if (unit === "mpy") { if (corrosionRate < 1) interpretation = "Corrosion Resistance: Outstanding"; else if (corrosionRate < 5) interpretation = "Corrosion Resistance: Excellent"; else if (corrosionRate < 20) interpretation = "Corrosion Resistance: Good/Fair"; else interpretation = "Corrosion Resistance: Poor/Unacceptable"; } resultInterpretation.innerHTML = interpretation; }

How to Calculate Corrosion Rate from Weight Loss

Calculating the corrosion rate is a fundamental process in materials science and engineering used to predict the lifespan of metal components. The Weight Loss Method (following ASTM G1 standards) is the most reliable way to determine the average corrosion rate over a specific period.

The Corrosion Rate Formula

The standard formula used in this calculator is:

CR = (K × W) / (A × T × D)
  • CR: Corrosion Rate
  • K: A constant that defines the output unit
  • W: Weight loss in grams (initial weight – final weight)
  • A: Total surface area exposed to the medium (cm²)
  • T: Time of exposure (hours)
  • D: Density of the material (g/cm³)

Choosing the Right Constant (K)

The constant K changes depending on whether you want your result in millimeters per year or mils (thousandths of an inch) per year:

Desired Unit K Value
mm/y (Millimeters per year) 8.76 x 104 (87,600)
mpy (Mils per year) 3.45 x 106 (3,450,000)

Common Material Densities

To use the calculator accurately, you need the density of the metal being tested. Here are common values:

  • Carbon Steel: 7.85 g/cm³
  • 304 Stainless Steel: 7.94 g/cm³
  • 316 Stainless Steel: 7.98 g/cm³
  • Aluminum (1100): 2.71 g/cm³
  • Copper: 8.94 g/cm³

Example Calculation

Suppose you have a Carbon Steel coupon with a surface area of 20 cm². After 720 hours (30 days) of exposure to a corrosive environment, it lost 0.12 grams of weight. The density of Carbon Steel is 7.85 g/cm³. You want the result in mpy.

Using the formula:

CR = (3,450,000 × 0.12) / (20 × 720 × 7.85)
CR = 414,000 / 113,040
CR = 3.66 mpy

This indicates "Excellent" corrosion resistance for most industrial applications.

Steps for Accurate Testing

  1. Cleaning: Before weighing, the metal must be cleaned of all grease and contaminants.
  2. Initial Weighing: Record the mass to at least 4 decimal places (0.0001g).
  3. Exposure: Ensure the sample is fully immersed or exposed as per the application environment.
  4. Post-Test Cleaning: Use a chemical or mechanical method to remove corrosion products (rust) without removing the base metal.
  5. Final Weighing: Record the final mass to determine total weight loss.

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