The effects of mechanical factors on crack growth behavior during the second stage of high pH stress corrosion cracking in pipeline steel were investigated by applying several loading scenarios on compact tension (CT) specimens. The main mechanism for stage 2 of intergranular crack propagation is anodic dissolution ahead of the crack tip which is highly dependent on crack-tip strain rate. The maximum and minimum crack growth rates were 3 × 10−7 mm/s and 1 × 10−7 mm/s, respectively. It was observed that several factors such as mean stress intensity factor, amplitude, and frequency of loading cycles determine the crack-tip strain rate. Low R-ratio cycles, particularly high-frequency ones, enhance secondary crack initiation, and crack coalescence on the free surface. This mechanism accelerates crack advance on the free surface which is accompanied with an increase in mechanical driving force for crack propagation in the thickness direction. These findings have implications for pipeline operators and could be used to increase the lifespan of the cracked pipelines at stage 2. For those pipelines, any loading condition that increases the strain rate ahead of the crack tip enhances anodic dissolution and is detrimental. Additionally, secondary crack initiation and coalescence could be minimized by avoiding internal pressure fluctuation, particularly rapid large pressure fluctuations.
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1 June 2020
SCIENCE SECTION|
March 17 2020
Effects of Loading Spectra on High pH Crack Growth Behavior of X65 Pipeline Steel
Hamid Niazi;
Hamid Niazi
*Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 1H9.
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Karina Chevil;
Karina Chevil
**TransCanada Pipeline Limited, Calgary, Alberta, Canada, T2P 5H1.
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Erwin Gamboa;
Erwin Gamboa
**TransCanada Pipeline Limited, Calgary, Alberta, Canada, T2P 5H1.
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Lyndon Lamborn;
Lyndon Lamborn
***Enbridge Pipelines Inc, Edmonton, Alberta, Canada, T5J 0T6.
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Weixing Chen;
Weixing Chen
*Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 1H9.
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Hao Zhang
Hao Zhang
‡
*Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 1H9.
‡Corresponding author. E-mail: [email protected].
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CORROSION (2020) 76 (6): 601–615.
Article history
Received:
December 14 2019
Revision Received:
March 16 2020
Accepted:
March 16 2020
Citation
Hamid Niazi, Karina Chevil, Erwin Gamboa, Lyndon Lamborn, Weixing Chen, Hao Zhang; Effects of Loading Spectra on High pH Crack Growth Behavior of X65 Pipeline Steel. CORROSION 1 June 2020; 76 (6): 601–615. doi: https://doi.org/10.5006/3472
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