Final answer:
To find the rate of corrosion, the weight loss is converted to volume using the density of steel, then the annual corrosion rate is calculated in both mils per year (mpy) and millimeters per year (mm/yr).
Step-by-step explanation:
The correct answer to the rate of corrosion experienced by a thick steel sheet near the ocean, given a weight loss of 485g over a square area of 250 in² and steel with a density of 7.9 g/cm³, can be calculated in two steps. First, we convert 250 in² to cm² and 485g to cm using the steel's density. Next, we establish the annual corrosion rate in mils per year (mpy) and millimeters per year (mm/yr).
Conversion of Area and Weight Loss to Volume
1 inch = 2.54 cm, hence 250 in² = 250 * (2.54 cm)^2 = 1612.9 cm²
Weight loss in cm³ = mass (g) / density (g/cm³) = 485 g / 7.9 g/cm³ = 61.39 cm³
Calculation of Corrosion Rate in mpy and mm/yr
Since corrosion depth = volume / area, we have:
Corrosion depth in cm = 61.39 cm³ / 1612.9 cm² = 0.038 cm/year
To get mpy, we convert 0.038 cm to mils: 0.038 cm = 15 mils/year (since 1 mil = 0.001 inch and 0.038 cm = 0.015 inch).
To get mm/yr, we use the conversion: 0.038 cm/year * 10 mm/cm = 0.38 mm/year.