Corrosion of pipelines in the presence of alternating current interference
Date
2012
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Abstract
With the increasing development of buried pipelines and the high-voltage power lines as well as the rail transit systems, pipelines encounter interference by alternating current (AC). It has been demonstrated that AC induced corrosion constitutes an essential threat to the pipeline integrity and safe operation. In this research, corrosion and AC corrosion of a 16Mn pipeline steel was studied in a simulated soil solution by weight loss testing, various electrochemical corrosion measurements, real-time AC/DC (direct current) signal analysis, and surface characterization. The results demonstrate that corrosion of the steel is within an acceptable level in the absence of AC interference. However, the corrosion rate of steel is enhanced remarkably by the applied AC current density from 0 to 400 A/m2. With the further increase to 600 A/m2 and 800 A/m2, the steel corrosion decreases. This is attributed to passivation of the steel at sufficiently high AC current densities. A high AC current density would generate high positive and negative AC potential components on the steel, resulting in the evolutions of hydrogen and oxygen, and enhancing the corrosion activity of the steel. Moreover, while AC could enhance corrosion of steel, only a very small percentage of AC current is involved in the steel dissolution. The vast majority of AC either participates in the charging-discharging process in the double-charge layer of steel electrode or gets involved in the red ox reaction of water. Furthermore, the presence of AC would decrease the cathodic protection (CP) effectiveness for protection of pipelines from corrosion. When CP is maintained at the potential of -0.85 V (saturated calomel electrode, SCE), the steel is not fully protected when i AC exceeds 100 A/m2. Only when the CP potential is sufficiently negative, such as at -1 V (SCE), the steel is under sufficient protection. The effect of AC on the CP performance depends on the potential applied on the steel. When the CP potential is not sufficiently negative, such as -0.85 V (SCE), AC would shift the corrosion potential of the steel negatively, increasing the corrosion reaction activity of the steel. When the CP potential is sufficiently negative, such as -1 V(SCE), the AC application would not be able to affect the steel corrosion at a detectable level.
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Bibliography: p. 89-95
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Citation
Su, X. (2012). Corrosion of pipelines in the presence of alternating current interference (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/4752