Research On The Influence Of AC Interference To The Corrosion Of Buried Pipeline Steel

The corrosion risk caused by AC is a relatively new phenomenon,and its corrosionbehavior is much more complex than that in the usual medium,so research method has certainpeculiarities and some difficulties.The AC induced corrosion behavior of familiar pipelinesteel Q235,X52and X65in soil were investigated mainly by indoor simulation,morphologyobservation,weight loss analysis and electrochemical measurement. Pertinent experiment dataare provided for the buried metallic pipeline in design,construction and the protection ofcorrosion.The paper is mainly divided into three parts:AC interference laboratory simulationexperiment,AC corrosion test and electrochemical experiment.Research on the ACinterference effect to the corrosion of buried pipeline steel as the following aspects:(1) theinfluence of AC voltage, soil resistivity, height between transmission lines and pipeline, spatialrelationship between power lines and pipeline to the induced voltage on the surface of thepipeline(2) modeling with Right-of-Way software package, predicting the degree ofinterference and comparing the experimental results with the software results (3) the influenceof AC interference voltage, expose area of the specimen, chemical composition of the pipelinesteel, soil resistivity and pH value of the soil to the corrosion morphology and rate of thecarbon steel(4)the effect of AC interference to the Polarization curve and AC impedancespectroscopy.The results show that the induced voltage and current increase as the AC voltageincreases,decrease as the height and soil resistivity increase and maximize when the pipelineparallels the AC lines.The software simulation results are smaller than the experimentalresults.Existence of AC can enhance corrosion rate under those conditions in which it would in any case start,but would otherwise proceed slowly as a protective layer builds up.Thepolarisation tests confirmed that AC has a strong influence on corrosion kinetics and oncorrosion and equilibrium potential.Generally,in the presence of AC,corrosion potential isshifted toward the negative direction and the exchange current density increases.Therelationship between expose area and weight loss indicates:with expose areaaccretion,specimens’ corrosion rates trend to minish.Experiment results indicate:alternatingcurrent corrosion have relation with voltage,soil resistivity,average current density,expose area,chemical composition of pipeline steel and so on.