| The buried pipelines applied to cathodic protection were able to generate stray current interference for near unprotected pipelines.This was also one of the important reasons for the formation of stray current corrosion.Aiming at stray current interference to cathodic protection system and unprotected pipelines generated by impressed current cathodic protection system,mathematical model of stray current corrosion was built in this paper,and the prominent factors of affecting soil resistivity were also explored.Meanwhile,the effects of stray current on the potential distribution of cathodic protection and the interference of stray current to unprotected pipelines under different factors were systematically studied,and the optimal drainage protection measure was confirmed.This paper mainly completed the following work:(1)The mathematical model of the potential distribution of stray current corrosion field was improved,and soil resistivity was considered in the model.Simulation software was adopted to solve the model.The experimental verification system was established.The reliability of mathematical model and method were verified by comparison with the experimental results and numerical simulation results which were basically consistent.(2)Taking into account the important effect of the variation of soil resistivity around the buried pipeline on the influence of stray current corrosion,the grey relational analysis method was applied to analyze correlative degree of the factors which effected on soil resistivity,and the prominent factors of soil resistivity were determined.Then,lab experiments were carried to analyze and summarize the regularity of soil resistivity changing with the prominent factors.(3)The interference of stray current to the potential distribution of cathodic protection in the layout of crossed and paralleled pipelines was analyzed.The results showed that the interference between pipelines was mutual.The protected pipelines being in the state of under protection due to loss of protected current threatened the safe operation of them,while the potential of the unprotected pipelines in the current flowing out position rose and the interference of stray current increased.The magnitude of protected current,laying spacing of pipelines,parameter of coating,soil resistivity,soil temperature,water content and otherfactors were systematically analyzed for the influence of the potential distribution of unprotected pipeline.The simulation results showed that:The greater protection current was,the stronger the interference degree.The larger spacing of crossed or paralleled pipelines was,the lower the influence of unprotected pipeline.Improving the quality of coating of protected pipeline to increase coating resistivity was helpful to enhance its cathodic protection potential,and the interference for unprotected pipelines was reduced.The larger the soil resistivity was,the harder unprotected pipelines were corroded by stray current.The potential of unprotected pipelines rose as the soil temperature and water content increased,and the interference of stray current enhanced.(4)Finally,drainage protection measures of DC stray current were introduced.Aiming at the characteristics of mutual interference between pipelines when unprotected pipelines existed in the impressed current cathodic protection system,the method of drainage by grounding was used to suppress the effect of stray current.Practice at site had proved that the result of drainage by grounding was outstanding and could effectively suppress the interference of starry current.At the same time,the cathodic protection of protected pipelines was improved. |
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