Electrochemical Study On The Impact Of The AC To Buried Pipeline

Traditional experiences showed that the current generated by AC could not cause corrosion of pipelines,and the main hazard was that the fault current threated to human security. But in recent years, people have awared that AC(such as the high-voltage transmission lines) would cause corrosive threat to the buried pipeline. The corrosion risk caused by AC is a relatively new phenomenon, and its corrosion behavior is much more complex than that in the usual medium, so research method has certain peculiarities and some difficulties.In order to quickly and accurately determine the corrosion rate over time of the metal material in the soil medium, this paper choosed test solution to simulate Qingdao soil for laboratory research of the pipeline corrosion interfered by AC. By measuring the X70 steel corrosion potential changing with time,polarization curves and AC impedance I studied the variation of electrochemical parameters on the X70 steel interfered by AC, as well as the changes of corrosion rate and thus studied initialy mechanism of soil erosion under the interference of AC. The results showed that when X70 steel was interfered by certain AC its corrosive potention was decrescent,its corrosive current was accrescent, and the process of corosion was changed from cathoding control to blending control,then corrosion rate increased.The cathodic protection could inhibit the exchange of corrosion to a certain extent. But in the AC interference protection standards, the continued use of carbon steel protection of potential(-770mVSCE) in neutral solution is not necessarily appropriate, so it is very important to select the most appropriate protection potential for inhibiting corrosion, energy conservation and preventing the harm caused by excessive protection under the AC voltage interfere. This paper proposed the use of the best potential in stead of the protection potential. Used electrochemical methods to research the corrosion characteristics of the X70 steel under different alternating stray current (AC)voltage and got polarization curves,potentiostatic polarization experiments and electrochemical impedance spectroscopy(EIS) under different cathodic polarization potential to determine the scope of its cathodic protection potential and the optimum cathodic protection potentia. The results showed that the use of polarization curves,potentiostatic polarization experiments and electrochemical impedance spectroscopy could determine the conditions of cathodic protection parameters of the X70 steel under different AC voltage.At last I suggested that in my experiment conditions the smallest cathodic protection potential of the X70 steel under different AC at a smaller voltage was -815mVSCE ,while at a larger selected -835mVSCE around and the optimum cathodic protection potential under different AC at a smaller voltage was -900mVSCE ,while at a larger selected -1000mVSCE around.