Which expression correctly defines the corrosion rate in a coupon test?

• A. CR = (A × t) / (K × W).
• B. CR = (W) / (A × t).
• C. CR = (K × W) / (A × t).
• D. CR = (K × A) / (W × t).

Answer: (C)

In a coupon test, the corrosion rate represents how much metal is lost per unit area per unit time, adjusted to standard units with a conversion constant. You weigh the coupon after exposure to get the weight loss (W), know the exposed area (A), and the exposure time (t). Then the rate is CR = (K × W) / (A × t). The weight loss in the numerator, scaled by K, gives the amount of material removed, while the denominator normalizes by how much area was exposed and for how long, so results can be compared across different coupon sizes and test durations. This formulation captures the idea of rate as loss per area per time. The other forms would either imply the rate increases with area or time in the wrong way, omit the essential conversion constant, or place terms in a way that does not represent loss per area per time.