applied fracture mechanics

Early Corrosion Fatigue Damage on Stainless Steels Exposed to Tropical Seawater:A Contribution from Sensitive Electrochemical Techniques 241until the end of polarisation. The increase of current as a function of time can be associatedwith two processes taking place under potentiostatic polarization: mainly the activedissolution of nucleated pits (one to three pits) and the simultaneous dissolution of themetal surface in the passive state. From the integration of the area beneath the curve currentvs time the electric charge was obtained, from which the quantity of dissolved metal per pitwas calculated using Faraday's law according to the chemical composition of the 304stainless steel [55].Figure 7. Chronoamperometries obtained during potentiostatic generation of pits in a 304 stainless steelin natural seawater in stationary conditions. Polarisation at 300 mV vs SCE for: a) 5, b) 30 and c) 60minutes.And the other hand, Figure 8 shows the amount of material dissolved as function of time ofanodic polarization, also includes the fit (solid and dotted lines) performed through thefollowing power equation:DMACd ct(7)where DMAC is the amount of dissolved material per pit in g obtained fromchronoamperometries, t is the pit growth time (or anodic polarization time) in minutes and,c and d are constants.Once determined the amount of dissolved material per pit as a function of anodicpolarization time and knowing the density of stainless steel (= 8.03 g/cm 3 ), the volume ofdissolved metal was determined. Using a material removal procedure described in detail byGonzalez Sanchez and Dzib-Pérez [40-55] to determine the pit depth as a function of time ofanodic polarization the empirical pit growth law was established for corrosion pits in 304stainless steel. Figure 9 shows the Maximum Pit Depth (MPD), generated in 304 steelsamples, as a function of time under anodic polarisation.