Development of a real-time AC/DC data acquisition technique for studies of AC corrosion of pipelines

In this work, the alternating current (AC), 60 Hz in frequency, corrosion of 16Mn pipeline steel was studied in a simulated soil solution by weight loss and polarization curve measurements, real-time AC/DC (direct current) signal data acquisition (DAQ), and surface characterization. The developed DAQ is capable of separating the DC and AC voltage components from the recorded total reading, providing mechanistic information about the steel corrosion in the presence of AC interference. The corrosion of steel is enhanced 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 corrosion rate of the steel decreases, which is attributed to the formation of a compact corrosion product layer on the steel surface at sufficiently high AC current densities, and a compact film is formed on the steel surface. While AC could enhance corrosion of the steel, only a very small percentage of AC current is involved in the steel dissolution (acts as Faradaic current). The vast majority of AC either participates in the charging–discharging process (acts as non-Faradaic current) of the double-charge layer or gets involved in the redox reaction of water.

► A data acquisition technique is developed, capable of separating the DC and AC potentials from the recorded potential signal.
► The effect of AC current density on corrosion of 16Mn pipe steel is determined.
► The AC corrosion mechanism of the steel is analyzed.
► A potential method to calculate AC current density on pipelines in the field is proposed.