Corrosion in Metals: Introduction, Classification and Rate | Metallurgy
Corrosion penetration rate = K (ai / nd) where, a is the atomic-weight of the metal, i is the current density in micro-amperes per cm 2, n is the number of electrons lost, D is the density in g/cm 3. K is a constant. For most applications, a corrosion penetration rate less than about 20 mpy (0.50 mm/yr) is acceptable.