Corrosion Rate Calculator (Weight Loss, mm/year and mpy)
Corrosion rate from the weight a test coupon loses, in mm per year, mils per year and µm per year, with the wall left after a number of years and the years until it reaches a minimum.
Results
The dashed line marks the value you entered.
What this tool does
The weight-loss method of ASTM G1 and G31 exposes a coupon of known area, cleans off the corrosion product and weighs the loss: CR = K·W ÷ (A·t·D), with K = 87.6 when W is in mg, A in cm², t in hours and D in g/cm³ to give mm per year. One millimetre a year is 39.4 mils per year (mpy), the US unit. This is an average over the whole surface: pitting, crevice and galvanic attack can eat through a wall far faster than the average suggests, and rates are not constant over time. Use the remaining-life figure as a rough estimate only.
Formula
CR (mm/year) = 87.6 × W ÷ (D × A × t) (W in mg, D in g/cm³, A in cm², t in hours) · mpy = 39.37 × mm/year
Variables
| Symbol | Meaning | Unit |
|---|---|---|
wl | Mass lost by the coupon | mg |
ar | Exposed surface area | cm² |
hr | Exposure time | h |
de | Density of the metal | g/cm³ |
wt | Wall thickness now | mm |
tm | Minimum wall thickness you need | mm |
yr | Years of service to look ahead | years |
CR | Corrosion rate | mm/year |
MP | Corrosion rate in mils per year | mpy |
UM | Corrosion rate in micrometres per year | µm/year |
WL | Wall left after those years | mm |
LF | Years until the wall reaches the minimum (0 if no loss) | years |
Worked example
- Mass lost by the coupon85 mg
- Exposed surface area20 cm²
- Exposure time720 h
- Density of the metal7.86 g/cm³
- Wall thickness now6 mm
- Minimum wall thickness you need3 mm
- Years of service to look ahead5 years
- Corrosion rate0.0658 mm/year
- Corrosion rate in mils per year2.59 mpy
- Corrosion rate in micrometres per year65.8 µm/year
- Wall left after those years5.67 mm
- Years until the wall reaches the minimum (0 if no loss)45.6 years
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.