海水流速对经抛光和钝化表面处理的2205不锈钢点蚀的影响

Effect of Seawater Flow Velocity on Pitting Corrosion of 2205 Stainless Steel with Different Surface Treatments

采用动电位极化曲线、电化学阻抗谱以及Mott-Schottky曲线等电化学测试方法研究了2205不锈钢管路材料在流动海水中的耐点蚀性能,并对测试后的试样进行了腐蚀形貌观察。结果表明,抛光状态和钝化状态下,试样表面均出现了明显的点蚀形貌,点蚀电位在0.9~1.2 V之间。在静态环境中材料的耐点蚀性要强于流动海水中;随着流速上升,材料的耐点蚀性并未发生明显变化,但表面钝化膜在流动海水中失去了再钝化能力。2205不锈钢表面钝化膜呈现n型和p型两种半导体特征,说明不锈钢表面钝化膜呈现双层结构,主要由外层Fe的氧化物和内层Cr的氧化物组成。钝化处理后试样的耐点蚀性能有所上升,但钝化膜的半导体性质未发生明显变化。海水冲刷使得不锈钢耐点蚀性能下降,不同表面处理的2205不锈钢在海水冲刷下表面钝化膜特性差异导致不锈钢点蚀敏感性不同。

2205 stainless steel is commonly used in pipeline systems.In the presence of flowing seawater 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 behavior 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 potentiodynamic 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 obvious pits formed on the surface of either the polished or passivated steel, with pitting potentials rangingfrom 0.9 V to 1.2 V. The pitting resistance of the steel is higher in static seawater rather than in flowingseawater, 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 passivationfilm 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 thesteel increased, but the semiconductor properties of the passivation film did not show significant changes.The flowing seawater could reduce the pitting corrosion resistance of the steel, but the difference inthe surface passivation film characteristics of the steel pre-treated by two methods could result in differentsensitivity to pitting corrosion of the 2205 stainless steel in flowing seawaters.