A simulated occluded corrosion cell (OCC) was used to study the chemical changes within corrosion cracks or crevices of mild steel (A3) in 0.01 mol·L-1 NaCl solution at 50 掳C . It was found that as anodic currents passing the cell

the pH value fell quickly at the beginning while slowly after it reached about 6

which was proportional to the quantity of passing electricity. Meanwhile the Cl- migrated into occluded cell. The Cl- migration was proportional to the time of current flowing

and a linear relation also existed between Cl- migration per mm2 of anode area per hour and current intensity

while for each mol Cl- migrated almost always 1.5～1.6 F of electricity passed. This relationship did not change whatever the current density and the time were.