A Study On Electrochemical Technology For Corrosion Detection And Monitoring Of Stainless Steel In Marine Atmosphere Environment

Stainless steel is a widely used metal material in marine engineering.However,due to the high concentration of Cl-in the marine atmosphere environment,the corrosion of the material is general.The excessive corrosion and failure of stainless steel components are very serious.It's a threat to the development and security of China's marine industry Therefore,it's necessary to evaluate the corrosion resistance of materials and prolong their service life.In this paper,the atmospheric corrosion detection probe(symmetric electrode system)and the electrochemical sensor(asymmetric electrode system)are used to study the corrosion behavior of 304SS,2205DSS and 316LSS in the simulated ocean atmosphere.A theoretical model for electrochemical noise data analysis based on Thevenin electrochemical equivalent circuit(EEC)model was established.The relationship between the electrochemical noise(EN)characteristic parameters measured by different electrode systems and the corrosion rate is obtained.The passivation effect of 304SS in alkaline phosphate-molybdate solution was evaluated by EIS technique.The Thevenin equivalent circuit model analysis shows that the relationship among the noise resistance(R_n),the spectral noise resistance(R_sn)and the impedance modulus(Z)is R_n=R_sn=(?)for the symmetrical electrode system when electrode's impedance is much larger than the solution resistance R_s.R_n and R_sn can be used as the evaluation standard of corrosion.Since Rn and Rsn are affected by Rs and the impedance modulus of the working electrode and the counter electrode for asymmetric electrodes system,it should be cautious to use R_n and R_sn as the evaluation standard of corrosion.The results of EN detection of 304SS,2205DSS and 316LSS show that in simulated marine atmospheric environment,the stainless steel passivation film is relatively complete at the initial stage and the corrosion rate is slow.With the deposition and erosion of Cl-on the surface of stainless steel,pitting begins to occur and the corrosion rate increases.The initiation process of pitting on the surface of stainless steel is random,and part of the active pores can still be re-passivated.The passivation film of stainless steel is sensitive to relative humidity and Cl-concentration.With the increase of relative humidity and the increase of Cl-concentration,the corrosion resistance decreases and the corrosion rate increases.After treated in alkaline phosphate-molybdate passivation solution,the surface of 304SS forms a uniform passivation film rich in phosphorus element.The corrosion resistance of stainless steel has improved.In the passivation process,molybdate and phosphate are synergistic.The passivation effect is sensitive to the passivation temperature and time.