| With the development of oceanographic engineering, the corrosion of metal has been the main restraining factor of deep sea development. Because of the character of high cost, difficult recycling and the data can’t be accumulated easily, the study method of field experiment is used rarely. Most of the researches are done by laboratory simulation. In this paper, a simulative deep sea pressure vessel with the volume of 100L was designed and constructed. The pressure of this vessel can reach 16MPa, it is stable and safe. All of the experiments in this paper were done in the device. The stability and applicability of high purity Zn reference electrode and the activate property of Al-Zn-In-Mg-Ti high activated sacrificial anodes in the circumstance of deep sea with high pressure were studied. And how the pressure of sea water influenced the cathodic protection potential distribution of low alloy steel was also researched. Galvanostatic polarization, cyclic voltammetry of small range, electrochemical impedance spectroscopy (EIS) were used to analyze the properties of high purity Zn reference electrode and Al-Zn-In-Mg-Ti high activated sacrificial anodes.By studying the stability and applicability of high purity Zn reference electrode, the results showed that the electrode potential of high purity Zn reference electrode turned to be stable after it steeped in the sea water for 30 hours. The value of electrode potential was about -1040mV, the undulating quantity was ±3mV, it can satisfy the request of reference electrode. The result of electrochemical impedance spectroscopy (EIS) showed that the electrode process of high purity Zn reference electrode was controlled by diffusion. After the experiment of Galvanostatic polarization, the electrode potential of high purity Zn reference electrode had negative shift for 4mV and it could be stable after it was charged with electricity for 7000 seconds, it can satisfy the request of electrochemical measurement. The cyclic voltammetry of small range showed that oxidation and reduction peaks can’t coincide totally, the reversibility of high purity Zn reference electrode was not very good. In the solution of KOH, with the slowing down of scanning speed, the potential difference between oxidation and reduction peaks decreased, the degree of electrode’s reversibility increased. So the high purity Zn reference electrode can be used in steady-state measurement when the scanning speed is low.The activated property differences of Al-Zn-In-Mg-Ti high activated sacrificial anodes between the sea water with high pressure and ordinary pressure have been researched. The results showed that when the pressure of sea water was 15.5MPa and the temperature was 4℃, the open circuit potential, electrochemistry capacity and current efficiency were lower than they were in the sea water of ordinary pressure. After 4 days’experiment of accelerating corrosion in the sea water of 15.5MPa, the dissolving feature of Al-Zn-In-Mg-Ti high activated sacrificial anodes was not good. On the surface of sacrificial anodes, it was not dissolved uniformly, and some large areas even didn’t dissolve. It indicated that the activated properties of sacrificial aluminium alloy anodes were worse when in the circumstance of high pressure, and some part of the surface did not activated effectively. The high efficiency sacrificial anodes techniques that have the resistance of high pressure need to be exploited.The influence of sea water’s pressure to the cathodic protection potential distribution of low alloy steel was researched. The results showed that the self-corrosion potential of mild steel hardly changed as the increasing of the sea water’s pressure, the potential was about 0.31mV. Both of the anode process and cathodic process were decreased a little as the sea water’s pressure increasing. However, the limited current density of mild steel decreased, the ultimate resistance increased, the corrosion rate decreased and the polarization parameter became higher, it leaded the cathodic protection potential distribution increased a little. That means the increasing water pressure will not aggravate the nonuniformity of potential distribution, it will improve the uniformity of potential distribution and increases the scale of cathodic protection. Because of the small space of pressure vessel, the change of polarization parameter that caused by distance was too little, it didn’t lead the obvious change of cathodic protection scale. The potential of each measure point on the surface of mild steel didn’t change a lot as the water pressure increasing. |
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