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51315-5588-Corrosion Behavior of Buried Pipeline in Presence of AC Stray Current in Controlled Environment

Picture for Corrosion Behavior of Buried Pipeline in Presence of AC Stray Current in Controlled Environment
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Product Number: 51315-5588-SG
ISBN: 5588 2015 CP
Author: Elmira Ghanbari
Publication Date: 2015
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AC corrosion is a frequent problem where pipelines share right of way with high power transmission lines or AC powered railed system. In these shared utility corridors the magnetic field produced by transmission power line induces an AC electric current on the buried pipe the magnitude of the AC current being proportional to the voltage and separation distance. AC corrosion can occur even when the cathodic protection (CP) criteria is deemed to be satisfied. This is due to the fact that AC interactions are not well understood and several aspects of it have yet to be clarified. In the present work corrosion current densities on carbon steel samples in sodium chloride solutions with and without the AC at different DC bias potentials are obtained by electrochemical and weight loss analysis. These data are compared and discussed together with polarization curves to obtain an assessment of electrochemical techniques which are commonly applied for evaluation of AC induced corrosion. By comparing real corrosion current density (Faradic current density) from weight loss test with that of the polarization curve a correlation between the two could be obtained. Additionally solution analyses are carried out during the test to quantify the iron ion contents and the pH of the solution. During the experiment magnetic stirring and continuous replacement of solution were applied in order to maintain a constant pH and Iron ion content. These results are discussed in the context of differences in the anodic and cathodic Tafel slopes. In addition to these results we will also present data that shows that AC exposure was associated with a carbon rich surface film as well as cracking.
AC corrosion is a frequent problem where pipelines share right of way with high power transmission lines or AC powered railed system. In these shared utility corridors the magnetic field produced by transmission power line induces an AC electric current on the buried pipe the magnitude of the AC current being proportional to the voltage and separation distance. AC corrosion can occur even when the cathodic protection (CP) criteria is deemed to be satisfied. This is due to the fact that AC interactions are not well understood and several aspects of it have yet to be clarified. In the present work corrosion current densities on carbon steel samples in sodium chloride solutions with and without the AC at different DC bias potentials are obtained by electrochemical and weight loss analysis. These data are compared and discussed together with polarization curves to obtain an assessment of electrochemical techniques which are commonly applied for evaluation of AC induced corrosion. By comparing real corrosion current density (Faradic current density) from weight loss test with that of the polarization curve a correlation between the two could be obtained. Additionally solution analyses are carried out during the test to quantify the iron ion contents and the pH of the solution. During the experiment magnetic stirring and continuous replacement of solution were applied in order to maintain a constant pH and Iron ion content. These results are discussed in the context of differences in the anodic and cathodic Tafel slopes. In addition to these results we will also present data that shows that AC exposure was associated with a carbon rich surface film as well as cracking.
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