Which measurement method directly yields the metal thickness loss used to calculate corrosion rate?

• A. Surface roughness measurement.
• B. Color change measurement.
• C. Weight loss measurement, from which thickness loss is calculated.
• D. Corrosion potential measurement.

Answer: (C)

The main idea here is measuring how much metal has actually been removed during exposure. The weight loss method does this directly: you weigh the specimen before and after the exposure period, and the difference gives you the mass loss due to corrosion. That mass loss can then be converted into thickness loss using the area and the material’s density (Δt = Δm / (ρ × A)). Once you have the thickness lost, you can compute the corrosion rate by dividing by the exposure time, giving a rate in units like mm/year or mils/year.

Other approaches don’t quantify how much metal has been removed. Surface roughness looks at changes in surface texture, not total material loss. Color change tracks corrosion products or appearance, not actual thickness. Corrosion potential reflects the electrochemical tendency to corrode, not the amount of metal dissolved.