General attack corrosion is usually measured in terms of

• A. Penetration rates per unit of time in millimeters per year or mils per year.
• B. Weight loss per year.
• C. Corrosion potential difference.
• D. Surface roughness change per year.

Answer: (A)

Uniform general attack reduces material thickness across the surface, so the most meaningful way to quantify it is by how fast that thinning occurs. The penetration rate, expressed as depth lost per unit time (millimeters per year or mils per year), directly reflects the amount of material remaining and is the most straightforward measure of service life under general corrosion. While weight loss can be used to estimate corrosion rate, it depends on surface area and the nature of the corrosion products, and it doesn’t translate into a direct thickness loss without extra calculations. Corrosion potential difference is an electrochemical indicator of driving force, not the rate of metal loss, and surface roughness changes describe topography rather than the overall thinning rate.