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04208 Laboratory Testing on the Influence of Alternated Current on Steel Corrosion

Product Number: 51300-04208-SG
ISBN: 04208 2004 CP
Author: Marco Ormellese, Sara Goidanich, Luciano Lazzari, Mariapia Pedeferri, and Fabio Bolzoni, Politecnico
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Studies on AC interference grew up in the last 30 years. For direct stray current corrosion on buried structures there is large agreement on criteria to be used for corrosion mitigation and international standards are available since many years. AC corrosion mechanism is not yet understood and reliable techniques for the determination of the corrosion risk are not yet available. This paper illustrates the results of laboratory tests on the influence of AC interference on carbon steel and galvanized steel corrosion in seawater, soil and concrete simulating solutions. The changing of the Tafel plot is compared with the results of theoretical models reported in literature. In the concrete simulating solutions the AC interference leads to a considerable decrease on the critical chloride threshold for pitting corrosion occurrence. The tests in seawater simulating solution revealed that the AC causes a localized corrosion also when not expected. Keywords: AC interference , Tafel parameters, corrosion kinetic, corrosion mechanism. INTRODUCTION Studies on AC interference grew up in the last 30 years, although AC corrosion was well known since the beginning of the XX century 1 . Today the main concern is the frequent parallelism between buried pipelines and AC high tension transmission lines in combination with the use of high dielectric coatings like extruded polyethylene or polypropylene. This co-location often results in induced AC voltages and currents on a pipeline that can cause depolarization effects leading to an increase of the corrosion rate and the breakdown of a passive layer, promoting pitting corrosion 2-5 . In the literature cases of corrosion due to the presence of AC stray current are reported 6-11 on pipelines cathodically protected to more negative values than -0.85 V with respect to Cu/CuSO 4 reference electrode.
Studies on AC interference grew up in the last 30 years. For direct stray current corrosion on buried structures there is large agreement on criteria to be used for corrosion mitigation and international standards are available since many years. AC corrosion mechanism is not yet understood and reliable techniques for the determination of the corrosion risk are not yet available. This paper illustrates the results of laboratory tests on the influence of AC interference on carbon steel and galvanized steel corrosion in seawater, soil and concrete simulating solutions. The changing of the Tafel plot is compared with the results of theoretical models reported in literature. In the concrete simulating solutions the AC interference leads to a considerable decrease on the critical chloride threshold for pitting corrosion occurrence. The tests in seawater simulating solution revealed that the AC causes a localized corrosion also when not expected. Keywords: AC interference , Tafel parameters, corrosion kinetic, corrosion mechanism. INTRODUCTION Studies on AC interference grew up in the last 30 years, although AC corrosion was well known since the beginning of the XX century 1 . Today the main concern is the frequent parallelism between buried pipelines and AC high tension transmission lines in combination with the use of high dielectric coatings like extruded polyethylene or polypropylene. This co-location often results in induced AC voltages and currents on a pipeline that can cause depolarization effects leading to an increase of the corrosion rate and the breakdown of a passive layer, promoting pitting corrosion 2-5 . In the literature cases of corrosion due to the presence of AC stray current are reported 6-11 on pipelines cathodically protected to more negative values than -0.85 V with respect to Cu/CuSO 4 reference electrode.
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