Preliminary Study On Cathodic Protection Of Typical Marine Steel In Simulated Flowing Seawater And Cavitation Corrosion

Cathodic protection technology gets more and more applications in steels used inseawater.16Mn,304L,316L and Q235are the materials always used in marineenvironment, however, the parameters of cathodic protection in materials underflowing seawater hasn’t been investigated. In this work, experiments which simulatethe circumstance of seawater were developed. The reasonable parameters of cathodicprotection in many materials were identified and the effects of cavitation on cathodicprotection were also investigated, which provides some references to practicalengineering and theoretical study. Results shown as following:Under simulating seawater, electrochemical impedance spectroscopy andcathodic polarization curves were analyzed jointly, the relation between the chargetransfer resistance and cathodic protection potentials E were obtained through thefitting of equivalent circuit, the optimum protection potentials and hydrogen evolutionpotentials under the flowing rate2m/s,4m/s and6m/s were identified in16Mn,304L,316L and Q235. At the same time, through the analysis of cathodic polarizationcurves under varieties of flowing rate in materials mentioned above, the effects howvelocity affect corrosion potential of these materials.The weight loss experiments of16Mn,304L,316L and Q235steel have beenexperimentally studied at flow rate2m/s,4m/s and6m/s with and without cathodicprotection. The results indicate that materials and flow rates will affect the protectiveeffect.In3.5%NaCl, through the analysis of EIS and corrosion morphology, theinvestigation on how cathodic protection affects cavitation of Q235was accomplished.The results show that cavitation is caused by both mechanical and electrochemicalfactors. Electrochemical corrosion can be curbed effectively by the cathodicprotection technology. The damages caused by cavitation will be weakened. However,the cathodic protection potential should be designed reasonably in practicalapplication to avoid the negative effects caused by more negative cathodic protectionpotentials to materials properties.