Electrochemical corrosion behaviours of AISI 304 austenitic stainless steel in NaCl solutions at different pH

The corrosion behaviour of austenitic AISI 304 grade stainless steel was studied in 3.5 wt. % NaCl solution. The pH of NaCl solution was controlled by the H2SO4 acid droplet. The OCP measurements were found that the corrosion behaviour of the steel specimens at different solution pH can be identified in the 1-2 hours of immersion period. After that the OCP curves were then remained horizontally linear up to 120 hours immersion. The low pH of NaCl solution recorded more electropositive OCP, whereas the high pH reduce its OCP value. The polarization analysis revealed by the Tafel plot shows the presence of aggressive anions (Cl− and SO42−) in the solution causes the metal surface more susceptible to the pitting corrosion. The high corrosion rate was occurred in low pH solution, whereas the rate of corrosion was relatively moderate at a high pH solution. The stereo microscope images show the worst pitting formation occur at pH 4 and its relatively decreases at higher pH solutions.