BIZOMAT MAKEOS · Materials
Corrosion Rate from Mass Loss
How fast is this metal corroding, and how long will the corrosion allowance last?
Uniform corrosion rate from a coupon’s mass loss, area, exposure time and density (ASTM G1 method), in mm/year and mils/year, with the remaining life of a corrosion allowance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Mass loss | mg | Mass loss after cleaning, from before and after weighing. |
| Exposed area | cm² | Total exposed surface area of the coupon. |
| Exposure time | h | Exposure time. |
| Metal density | g/cm³ | Density of the metal (carbon steel 7.86, stainless about 7.9, copper 8.96 g/cm³). |
| Remaining corrosion allowance | mm | Wall thickness still available before the minimum required thickness. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Mass loss
- What it is
- The mass the corrosion coupon lost during exposure, found by weighing it before exposure and again after cleaning off the corrosion products.
- Units and format
- Enter a number in mg: mg. The form accepts 0.000001 mg or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 mg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The corrosion rate rises in direct proportion to mass loss.
- Get it right
- Enter milligrams, not grams, and weigh after cleaning, not with the scale still attached.
What this means: Exposed area
- What it is
- The total surface area of the coupon that was exposed to the environment, including edges and both faces.
- Units and format
- Enter a number in cm²: square centimetres. The form accepts 0.000001 cm² to 100000000 cm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger area spreads the same loss thinner, so the rate falls in inverse proportion.
- Get it right
- Enter square centimetres; include the edges and subtract any masked or mounted area.
What this means: Exposure time
- What it is
- The time the coupon spent exposed to the environment, from installation to removal.
- Units and format
- Enter a number in h: hours. The form accepts 0.000001 h to 10000000 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 720 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer exposure for the same loss gives a lower rate.
- Get it right
- Enter hours: a 30-day exposure is 720 hours.
What this means: Metal density
- What it is
- The density of the coupon metal, used to turn mass loss into thickness loss.
- Units and format
- Enter a number in g/cm³: grams per cubic centimetre (1 g/cm³ = 1000 kg/m³). The form accepts 0.000001 g/cm³ to 25 g/cm³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7.86 g/cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rate falls in inverse proportion to density.
- Get it right
- Enter grams per cubic centimetre, not kilograms per cubic metre.
What this means: Remaining corrosion allowance
- What it is
- The wall thickness still available before the part reaches its minimum required thickness, used to estimate the remaining life at the measured rate.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Remaining life is this allowance divided by the rate, so it rises in proportion.
- Get it right
- Use the measured current thickness minus the minimum required thickness, not the original design allowance.
Method and formulas
- CR (mm/y) = 87.6 × W ÷ (ρ A T), W in mg, A in cm², T in hours.
- mils per year = mm/y × 39.37.
- Remaining life = allowance ÷ rate.
- Example: 120 mg lost from 20 cm² over 720 h is 0.092875 mm/y (3.6565 mpy).
Limitations
- Uniform corrosion only; pitting and crevice corrosion can perforate much sooner.
- Coupon conditions must represent the equipment (flow, temperature, deposits).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Evaluate corrosion coupons from tanks, cooling water or process lines
- Estimate remaining life from a corrosion allowance
- Compare materials in a test
Who it is for
- Materials engineers
- Maintenance and reliability engineers
- Water treatment specialists
What you get
- Corrosion rate in mm/year and mils/year
- Remaining life of the allowance
Interpreting the result
- Back up coupon results with thickness measurements on the equipment.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1500–1516. Topic reference; no source tables or recommended settings are reproduced.
- ASTM G1 Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Corrosion, salts and the humidity that matters
In Condensation Control by the Numbers
What it covers: Why metals corrode below the dew point, how salts take up water at set humidities, how to count wet hours, measure corrosion with coupons, and why CC-7's hygrostat moved from 75% to 65%.
Useful alongside · BIZOMAT original book
Corrosion surveys that find the worst wall
In Ultrasonic Testing by the Numbers
What it covers: Condition monitoring locations, spot readings and scanned bands, general and local wall loss, comparing surveys, corrosion coupons, and how to design a survey that finds the thinnest metal.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.