Combined Effect of Alternating Current Interference and Cathodic Protection on Pitting Corrosion and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in Near-Neutral pH Environment.

Liwei Wang,Zhongyu Cui,Zhifu Zhu,Lianjun Cheng,Shuowei Bai,Junru Li

doi:10.3390/ma11040465

Liwei Wang, Zhongyu Cui + Show 4 more

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https://doi.org/10.3390/ma11040465

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Journal: Materials	Publication Date: Mar 22, 2018
Citations: 26	License type: CC BY 4.0

Affiliation: Qingdao University, Ocean University of China

Abstract

Influence of alternating current (AC) on pitting corrosion and stress corrosion cracking (SCC) behavior of X70 pipeline steel in the near-neutral pH environment under cathodic protection (CP) was investigated. Both corrosion and SCC are inhibited by −0.775 VSCE CP without AC interference. With the superimposition of AC current (1–10 mA/cm2), the direct current (DC) potential shifts negatively under the CP of −0.775 VSCE and the cathodic DC current decreases and shifts to the anodic direction. Under the CP potential of −0.95 VSCE and −1.2 VSCE, the applied AC current promotes the cathodic reaction and leads to the positive shift of DC potential and increase of cathodic current. Local anodic dissolution occurs attributing to the generated anodic current transients in the positive half-cycle of the AC current, resulting in the initiation of corrosion pits (0.6–2 μm in diameter). AC enhances the SCC susceptibility of X70 steel under −0.775 VSCE CP, attributing to the promotion of anodic dissolution and hydrogen evolution. Even an AC current as low as 1 mA/cm2 can enhance the SCC susceptibility.

Highlights

With the increasing development of high voltage power transmission, its sharing common grid with oil and gas pipelines has brought huge risk to pipeline integrity [1,2]
cathodic protection (CP) hasMoreover, not reached of alternating current (AC) interference on corrosion of pipeline steels under CP
4, and steady-state values in densities under are different potentials illustrated in measurements, Figure 4, and the the CP

Summary

Introduction

With the increasing development of high voltage power transmission, its sharing common grid with oil and gas pipelines has brought huge risk to pipeline integrity [1,2]. Effect of AC on polarization behavior of metals has been modeled theoretically by Lalvani et al [4,5]. They related the AC caused change of corrosion potential and corrosion current density to the ratio between the anodic and cathodic Tafel slopes (indicated as r = βa /βc ). In their theory, corrosion kinetic parameters, such as Tafel slope and exchange current density are supposed to be invariable with the interference of AC. Our previous work [8] showed that AC interference changed the specific adsorption of chloride ions, which can influence the pitting susceptibility of mild steel [9]

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