A New Understanding on AC Corrosion of Pipeline Steel in Alkaline Environment
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JMEPEG (2017) 26:221–228 DOI: 10.1007/s11665-016-2416-6
A New Understanding on AC Corrosion of Pipeline Steel in Alkaline Environment M. Zhu and C.W. Du (Submitted July 22, 2016; in revised form August 29, 2016; published online November 4, 2016) In this work, the corrosion behavior of X80 pipeline steel at various frequencies AC was investigated in carbonate/bicarbonate solution using the polarization curve, EIS test, Mott-Schottky curve and immersion tests. A new understanding on AC corrosion of the steel in alkaline environment is proposed. Decreasing AC frequency negatively shifts the corrosion potential and increases the corrosion rate of steel, as well as corrosion pits occur more readily. The superimposed AC shifts the critical pitting potential negatively and degrades the passivity of the steel. AC reduces the compactness and uniformity of the passive film formed on the steel and increases the possibility of the breakdown of the film, as well decreases the film thickness. The application of AC could prevent the passive film forming on the surface of X80 steel and result in a destructive effect on the film formed on the steel surface, especially at the low-frequency AC. Keywords
AC corrosion, corrosion behavior, passive film, pipeline steel
1. Introduction With the rapid development of high-voltage AC power transmission lines, AC-powered rail transit systems and their sharing common right of way with the pipelines, the enhanced corrosion of metals (including pipeline steel) due to AC interference has been received more and more attention in the recent years (Ref 1-5). Xu (Ref 6) presented that the corrosion of 16Mn pipeline steel was enhanced due to the applied AC. Fu (Ref 7) found that an superimposed AC could increase the corrosion rate of carbon steel in carbonate/bicarbonate solution, and localized corrosion (pitting corrosion) has been observed on the steel surface. It is reported that (Ref 8) pitting could be initiated on the steel in both high pH and near-neutral pH solutions. Our previous research (Ref 9, 10) reported that AC could enhance the SCC susceptibility of X80 pipeline steel in carbonate/bicarbonate solution, and some cracks were found to have initiated from the pitting induced by AC current. Various models and theories (Ref 11-14) have been developed about the mechanism of AC corrosion. Although there have been increasing research on AC corrosion, the subject remains controversial. For example, Lalvani (Ref 2) indicated that AC could reduce anodic and cathodic polarizations, which is similar to the effect of a depolarization agent. Goidanich (Ref 12, 13) investigated the influence of AC on the corrosion kinetics parameters of metal materials, such as Tafel slope and exchange current density. Full agreement on the interpretation of the phenomenon of AC-induced corrosion has
M. Zhu, School of Mechanical Engineering and Automation, Zhejiang Sci-Tech University, Hangzhou 310018, China; and C.W. Du, Corrosion and Protection Center, University of Science and Technology Beijing, Beijing 100083, China
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