Calculate average uniform coupon corrosion in mm/year, micrometers/year, and mpy, reverse expected mass loss, or estimate the time to consume a separately determined usable thickness allowance at an assumed constant rate. This is not a safe service-life assessment.
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Corrosion Rate Formula
The following mass-loss formula estimates equivalent average uniform penetration after proper coupon cleaning and any required cleaning-loss correction. Include all exposed faces and edges in the area. It does not measure deepest pits or cracking. The constant uses a 365-day year.
- W = metal weight loss (mg)
- D = metal density (g cm⁻³)
- A = exposed area (cm²)
- t = exposure time (h)
How to Calculate Corrosion Rate?
The following two example problems outline the steps and information needed to calculate the Corrosion Rate.
Example Problem #1
- First, determine the metal weight loss (mg).
- The metal weight loss (mg) is calculated to be 50.
- Next, determine the metal density (g/cm³).
- The metal density (g/cm³) is measured to be 10.
- Next, determine the exposed area of the sample (cm²).
- The exposed area of the sample (cm²) is found to be 3.
- Next, determine the exposure time (h).
- This is given as 265 hours.
- Finally, calculate the corrosion rate using the formula above:
CR = 87.6 × W / (D × A × t)
The values provided above are inserted into the equation below and computed.
CR = 87.6 × 50 / (10 × 3 × 265) = 0.5509 (mm/year)
Example Problem #2
The variables required for this problem are provided below:
metal weight loss (mg) = 60
metal density (g/cm³) = 4
area of sample (cm²) = 5
time (hours) = 200
Test your knowledge using the equation and check your answer with the calculator.
CR = 87.6 × 60 / (4 × 5 × 200) = 1.314 mm/year
