MPY Corrosion Rate Calculator
Calculate corrosion rate in Mils Per Year (mpy) based on weight loss.
Mass lost in milligrams (mg)
Density in g/cm³ (e.g., Steel is ~7.85)
Exposed area in square inches (in²)
Duration of exposure in hours
Calculated Corrosion Rate
0.00 mpy
Metric Rate
0.00 mm/y
Classification
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About MPY Corrosion Rate Calculation
Corrosion rate is a critical metric in materials engineering, allowing professionals to estimate the lifespan of metal structures and piping systems. The standard unit of measurement in the United States oil and gas, chemical, and water treatment industries is MPY (Mils Per Year).
One "mil" is equal to one-thousandth of an inch (0.001 inch). Calculating the MPY allows engineers to determine how much thickness a material loses over a year due to corrosive processes.
The MPY Formula
This calculator uses the standard calculation method defined by ASTM G1 (Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens). The formula is:
MPY = (534 × W) / (D × A × T)
Where:
- W = Weight loss in milligrams (mg)
- D = Density of the specimen in grams per cubic centimeter (g/cm³)
- A = Area of the specimen in square inches (in²)
- T = Exposure time in hours
- 534 = Conversion constant based on the units used
Common Material Densities (g/cm³)
To use the calculator accurately, you need the density of the metal being tested. Here are common values:
| Material | Density (g/cm³) |
|---|---|
| Carbon Steel | 7.85 |
| Stainless Steel (304) | 7.90 |
| Stainless Steel (316) | 8.00 |
| Aluminum (Alloy 1100) | 2.71 |
| Copper | 8.96 |
| Brass (Yellow) | 8.47 |
| Titanium | 4.54 |
Interpreting Corrosion Rates
Understanding the severity of the corrosion rate helps in selecting materials and planning maintenance. While acceptable rates vary by application, general industry guidelines categorize corrosion rates as follows:
- Outstanding (< 1 mpy): Materials are expected to survive for many years. Suitable for critical parts.
- Excellent (1 – 5 mpy): Corrosion is slow. Material is generally acceptable for most applications.
- Good (5 – 20 mpy): Acceptable for heavy-wall tanks or piping where some material loss is planned for.
- Fair/Poor (20 – 50 mpy): Caution is advised. Regular inspection required.
- Severe (> 50 mpy): Material is likely unsuitable for the environment without protection.
How to Perform the Test
- Weigh Specimen: Clean and weigh the metal coupon to get the initial weight.
- Expose: Place the coupon in the corrosive environment for a specific time (T).
- Clean & Weigh: Remove the coupon, clean off all corrosion products according to ASTM G1 standards, and weigh it again to find the final weight.
- Calculate W: Subtract Final Weight from Initial Weight to get Weight Loss (W) in mg.
- Input Data: Enter W, Density (D), Area (A), and Time (T) into the calculator above.