Studies On Local Corrosion Behavior Of 304 Stainless Steel In Petrochemical Circulating Water

Local corrosion behavior of 304 stainless steel in simulate circulating water of low and high hardness and alkalinity with Cl^-was studied by electrochemistry measurements, means of simulated occluded cell and SEM, which could offer the theoretical foundation for the applications of 304 stainless steel in this circumstance.The anodic polarization behavior of 304 stainless steel in NaCl solution was studied by potential scanning technique. Potentiodynamic scanning polarization technique and electrochemical impedance spectroscopy (EIS) technique were applied to study the influence of stress on the corrosion sensitivity. The results of pitting corrosion potential test which showed that in solution of same Cl^-concentration, pitting corrosion potential in simulate circulating water of low hardness and alkalinity was 200mV more negative than that in solution of high hardness and alkalinity indicate that 304 steel is more sensitive to pitting corrosion in solution of low hardness and alkalinity. Determining skills in electrochemical noise were used to analysis standard deviation of different solutions which showed the relationship between characters and development of pitting corrosion and concentration of Cl^-. The stability of passive film of 304 stainless steel in simulate circulating water was studied by analyzing the spectrograms of electrochemical noise and electrochemical impedance spectroscopy. In simulate circulating water of same Cl^-concentration, the peak value of electrochemical noise was higher in solution of low hardness and alkalinity. It suggested that the stability of passive film in solution of high hardness and alkalinity was stronger. It may be the higher concentration of SO₄² which made the absorption of Cl^-more difficult.The chemical behavior within the occluded cell of 304 stainless steel in chloride solution during localized corrosion has been investigated by means of a simulated occluded cell. The rules of pH fall and enrichment in chloride ions in occlude cell were provided. Meanwhile, the simulated occluded solutions in different stages of different pH and chloride concentration were used to study the electrochemical behaviors of occluded cell corrosion.