Rust Decay Rate Calculator

Calculate the material loss over time based on metal exposure and weight reduction.

Carbon Steel is ~7.87

Analysis Results

Corrosion Rate: 0.00 mm/y

Mils Per Year: 0.00 mpy

function calculateRustRate() { var weightLoss = parseFloat(document.getElementById('weightLoss').value); var area = parseFloat(document.getElementById('surfaceArea').value); var time = parseFloat(document.getElementById('timeHours').value); var density = parseFloat(document.getElementById('metalDensity').value); var resultDiv = document.getElementById('rustResult'); if (isNaN(weightLoss) || isNaN(area) || isNaN(time) || isNaN(density) || area <= 0 || time <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Standard Corrosion Rate Formula: (K * W) / (A * T * D) // K (for mm/y) = 87.6 // W = weight loss in mg // A = Area in cm2 // T = Time in hours // D = Density in g/cm3 var mmy = (87.6 * weightLoss) / (area * time * density); var mpy = mmy / 0.0254; document.getElementById('mmyVal').innerText = mmy.toFixed(4); document.getElementById('mpyVal').innerText = mpy.toFixed(4); var severity = document.getElementById('severityLevel'); if (mmy < 0.02) { severity.innerText = "Classification: Outstanding Corrosion Resistance"; severity.style.backgroundColor = "#e8f5e9"; severity.style.color = "#2e7d32"; } else if (mmy < 0.1) { severity.innerText = "Classification: Excellent (Acceptable for most uses)"; severity.style.backgroundColor = "#fff9c4"; severity.style.color = "#f57f17"; } else if (mmy < 0.5) { severity.innerText = "Classification: Moderate (Caution Advised)"; severity.style.backgroundColor = "#ffe0b2"; severity.style.color = "#e65100"; } else { severity.innerText = "Classification: Poor (Rapid Material Failure)"; severity.style.backgroundColor = "#ffcdd2"; severity.style.color = "#c62828"; } resultDiv.style.display = 'block'; }

Understanding the Rust Decay Rate

Rust decay, scientifically known as atmospheric corrosion, is the electrochemical breakdown of metals when exposed to oxygen and moisture. For engineers, hobbyists, and maintenance professionals, calculating the corrosion rate is essential for predicting the lifespan of structures and determining when replacement is necessary.

How the Calculation Works

This calculator utilizes the standard industry formula derived from ASTM G1. It measures how many millimeters (mm) or mils (thousandths of an inch) of metal thickness are lost annually. The variables include:

• Weight Loss: The difference in mass of the metal sample before and after cleaning the rust off.
• Surface Area: The total area of the metal exposed to the corrosive environment.
• Exposure Time: The duration the metal was left in the environment (measured in hours).
• Metal Density: Every metal has a specific density; for example, Carbon Steel is 7.87 g/cm³, while Aluminum is 2.70 g/cm³.

Typical Metal Densities

Metal Type	Density (g/cm³)
Carbon Steel	7.87
Stainless Steel (304)	8.00
Copper	8.96
Aluminum	2.70

Practical Example

Imagine a carbon steel plate with a surface area of 50 cm² that was exposed to the coastal air for 1,000 hours (roughly 42 days). After removing the rust, the plate lost 300 mg of weight. Using the calculator, we find the corrosion rate to be approximately 0.0668 mm/year. This would be classified as "Excellent" resistance, suggesting the structure will last for many years before structural integrity is compromised.

Factors Accelerating Rust Decay

While the formula provides a mathematical average, real-world conditions vary based on:

1. Humidity: Moisture is a catalyst; humidity levels above 60% drastically increase rust formation.
2. Salinity: Salt acts as an electrolyte, accelerating the electrochemical reaction (common in coastal areas).
3. Pollutants: Sulfur dioxide and nitrogen oxides in industrial zones can lower the pH of moisture, making it more acidic and corrosive.
4. Temperature: Higher temperatures generally speed up chemical reactions, including oxidation.