Effects Of Alternating Current Interference On Corrosion Morphology Of The Buried Pipeline

Due to the low efficiency of alternating current(AC)corrosion,the amount of corrosion is 1%of direct current corrosion,the research of AC corrosion starts relatively late at home and abroad.With characteristics of strong randomness,variable direction and concentrated corrosion,there are greater probability of electrochemical reaction and more remarkable image of concentrated corrosion than DC corrosion.With the rapid development of electrified railways and high-voltage transmission lines,the corrosion problem of oil and gas pipelines is increasingly serious,so the research of corrosion behavior of X80 steel in simulated coastal soil solution is of great significance.In this paper,the research is based on X80 steel of the west-east gas transmission second line.Electrochemical testing method,weight loss method and corrosion morphology acquisition processing and eigenvalue analysis method were adopted to study the effect of AC interference on corrosion morphology,and a new method of evaluation of AC corrosion degree was put forward based on features.The main work and results are as follows:Firstly,in order to study the rules of corrosion potential of X80 steel in simulated soil solution and analyze polarization curves with no interference and various,different alternating current densities are applied to the electrochemical testing,and then discuss the corrosion behavior under AC interference preliminarily.The results show that,with the increase of AC densities,corrosion potential of X80 steel deviates positively and corrosion current density increases as the same.The effect of alternating current interference is more on cathode polarization of X80 pipeline steel than on anode polarization,when the formation and dissolution rate of the corrosion scale are similar,there are two values of corrosion potential in the polarization curve.Then,the paper studies the effect of AC densities,frequencies,chloride ion concentrations on corrosion morphology of X80 steel through immersion test indoors.The results show that when alternating current density is 150 A/m~2,there are obvious corrosion pits;with the continuous increase of alternating current density,the uneven surface,apparent local corrosion,diameter and depth of corrosion pit,rough pit edge and pitting factor increase significantly.When the interference frequency is lower(50?60?100 Hz),there are full of corrosion pits in the breeding stage with no significant measurable depth,in contrast,there are less corrosion pits in the smooth specimen when the frequency increases.It shows the synergy between AC interference and chloride ions,when the chloride ion concentration is more than0.5 mol/L,the pits and the edges present circular and flat respectively.Finally,this paper predicts a new method to evaluate AC corrosion degree and analyze corrosion morphology with eigenvalue by extracting a series of characteristic parameters and fractal dimensions based on MATLAB.The results show that there is a great correlation between energy,homogeneity and alternating current density,which be regarded as the measurement that become local corrosion from uniform corrosion.With the increase of AC density,2d and 3d fractal dimensions of corrosion image present linear growth and power growth respectively,some quantitative evaluations about AC interference can be obtained with eigenvalue and tendency.