Corrosion Rate Calculator - Weight Loss Method

This industrial-grade calculator determines the Corrosion Rate of a material based on the standard weight loss method (ASTM G1). It analyzes the severity of material degradation, estimates Service Life, evaluates Pitting Risk, and generates NACE-compliant severity reports.

1. Material Properties

Material Selection
Physical Properties
g/cm³

2. Test Parameters

Coupon Data
mg
hours
Geometry & Units
in²

3. Service Life & Pitting (Optional)

Life Estimation
mils
Pitting Factor

Engineering Insights: Corrosion Mechanics

1. The Governing Formula

The corrosion rate represents the depth of material penetration over time. It is derived assuming uniform corrosion across the entire surface area. The standard formula is:

$$ CR = \frac{K \cdot W}{D \cdot A \cdot T} $$

Where:

  • W: Weight loss (mg).
  • D: Density of the material (g/cm³).
  • A: Exposed surface area.
  • T: Exposure time (hours).
  • K: Constant to correct units (534 for MPY, 87.6 for mm/yr).

2. Units of Measurement: MPY vs. mm/yr

MPY (Mils Per Year) is the dominant unit in the US oil & gas industry. One mil is one-thousandth of an inch (0.001").
mm/yr (Millimeters Per Year) is the standard SI metric unit.
Conversion: 1 MPY = 0.0254 mm/yr. Conversely, 1 mm/yr ≈ 39.4 MPY.

3. Interpreting Severity (Typical Carbon Steel)

Acceptable rates depend heavily on the application (e.g., a pharmaceutical tank needs lower rates than a sewage pipe). However, general guidelines for Carbon Steel are:

  • < 1 MPY: Outstanding. Suitable for critical parts.
  • 1 - 5 MPY: Good. Typical allowance for piping.
  • 5 - 10 MPY: Fair. Inspect frequently. High corrosion allowance required.
  • > 10 MPY: Poor. Rapid failure likely. Consider upgrading material.

4. Uniform vs. Pitting Corrosion

This calculator assumes Uniform Corrosion (even wastage). It does not account for:
Pitting: Localized holes that can penetrate much faster than the calculated rate.
Galvanic Corrosion: Accelerated attack due to dissimilar metal contact.
Stress Corrosion Cracking (SCC): Sudden failure under tensile stress in corrosive environments.

For critical applications, a "Pitting Factor" is often applied to the calculated rate.

5. Environmental Factors

Corrosion rates generally double for every 10°C (18°F) increase in temperature. Other critical factors include:
Velocity: High flow removes protective oxide films (Erosion-Corrosion).
Aeration: Oxygen presence typically accelerates corrosion in water.
pH: Acidic (low pH) environments are generally more corrosive to steels.