Effect of Seawater Flow Velocity on Pitting Corrosion of 2205 Stainless Steel with Different Surface Treatments
2205 stainless steel is commonly used in pipeline systems.In the presence of flowing sea-water the failure of passivation film on tubing can easily lead to accidents such as pipeline leakage.Therefore,it is of great significance to acquire the impact of flowing seawater on the pitting corrosion be-havior of 2205 stainless steel with different surface treatments.Hence,2205 stainless steel was firstly subjected to polish-treatment and passivation-treatment respectively,and then the pitting behavior of which in flowing seawater was assessed by means of electrochemical testing methods such as potentio-dynamic polarization curve,electrochemical impedance spectroscopy,and Mott-Schottky curve as well as characterization of their morphology variation with corrosion process.It was found that there were obvi-ous pits formed on the surface of either the polished or passivated steel,with pitting potentials ranging from 0.9 V to 1.2 V.The pitting resistance of the steel is higher in static seawater rather than in flowing seawater,but as the flow rate increases,the pitting resistance of the steel does not change significantly,however,the surface passivation film loses its re-passivation ability in flowing seawater.The passivation film on the surface of 2205 stainless steel exhibits two semiconductor characteristics:n-type and p-type,indicating that the passivation film presents a double-layer structure,mainly composed of oxides of Fe(outer portion)and Cr(inner portion).After passivation treatment,the pitting corrosion resistance of the steel increased,but the semiconductor properties of the passivation film did not show significant chang-es.The flowing seawater could reduce the pitting corrosion resistance of the steel,but the difference in the surface passivation film characteristics of the steel pre-treated by two methods could result in differ-ent sensitivity to pitting corrosion of the 2205 stainless steel in flowing seawaters.
2205 stainless steelseawater pipelineerosion corrosionelectrochemistrypitting corro-sionpassivation film
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