Corrosion Behavior of X80 Pipe Steel under HVDC Interference in Sandy Soil

With the development of high voltage direct current (HVDC) systems, some pipelines have been badly interfered. The corrosion mechanism of pipelines has not been clearly clarified. In this work, laboratory experiments were designed to study the corrosion behavior of X80 steel under HVDC interference in sandy soil. The corrosion rates were related to the change in direct current (DC) density, which experienced three stages in the interference process. As soon as high DC interference voltage was applied to the working electrode, the current density increased sharply to a peak value in a few seconds. It then decreased rapidly to a steady value over dozens of seconds. Finally, it remained steady for the remaining time. With the measurement of local soil properties, the change in DC density was attributed to the local soil temperature increment, the water content decrement, and the substantial growth in the soil spread resistance. Moreover, the parameters contribute to the corrosion reaction during the interference process. The corrosion products were characterized at different times of interference via Raman spectroscopy. Lepidocrocite was produced under high DC density and then transformed to hematite under low DC density. Based on the above, the corrosion model during HVDC interference is proposed.