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Crack Growth Behavior of Pipeline Steels under Variable Pressure Fluctuations in a Near-Neutral pH Environment Open Access


Other title
fatigue crack propagation
near-neutral pH
minor cycles
pipeline steels
ripple load
variable amplitude fatigue
corrosion fatigue
Type of item
Degree grantor
University of Alberta
Author or creator
Yu, Mengshan
Supervisor and department
Chen, Weixing (Department of Chemical and Materials Engineering)
Examining committee member and department
Zhang, Hao (Department of Chemical and Materials Engineering, University of Alberta)
Chen, Weixing (Department of Chemical and Materials Engineering, University of Alberta)
Thomas R. Jack (University of Calgary)
Luo, Jingli (Department of Chemical and Materials Engineering, University of Alberta)
Ivey, Douglas (Department of Chemical and Materials Engineering, University of Alberta)
Li, Leijun (Department of Chemical and Materials Engineering, University of Alberta)
Department of Chemical and Materials Engineering
Materials Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
This research aims at understanding the crack propagation behavior of pipeline steels under variable pressure fluctuations in a near-neutral pH environment. Although pressure fluctuations have been recognized as the driving force for crack growth for more than two decades, the mechanisms governing their effects on crack growth have yet to be determined. Existing crack growth models that consider the effect of pressure fluctuations are established primarily by assuming a fatigue loading with constant stress amplitudes. This often yields a predicted life that well exceeds the service lifetime observed in the field. We believe that the significant discrepancies between laboratory findings and field observations could be bridged by modeling crack growth through a consideration of variable amplitude fatigue loadings, which are the conditions in the field. This investigation has focused on the evaluation of a variable amplitude fatigue waveform consisting of cycles with higher R ratios (minimum stress/maximum stress), termed as minor cycles, and periodic underload cycles with lower R ratios. Such a waveform is typical for the pressure fluctuations in pipeline discharge sections, which was performed both in air and in near-neutral pH solution. Compared with the corresponding constant amplitude loadings, the variable amplitude waveform significantly enhanced fatigue crack growth. The waveform was varied to study the effects of various contributing factors, including loading frequency, maximum stress intensity factor, number of minor cycles, and amplitudes of underload and minor cycles. By comparing results in near-neutral pH solution with that in air, the role of hydrogen and corrosion in crack growth was characterized and clearly defined. The obtained results agree with various failure scenarios found in the field, including the high frequency of failures found at the discharge sections of pipelines, and the different crack growth characteristics between oil pipelines and gas pipelines. Based on these findings, practical strategies were proposed for avoiding accelerated crack growth.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Mengshan Yu, Weixing Chen, Richard Kania, Greg Van Boven, Jenny Been. Depressurization-Induced Crack Growth Enhancement for Pipeline Steels Exposed to Near-Neutral pH Environments. IPC2014, Sept. 29 - Oct. 3, 2014, Calgary, Canada. Paper No. IPC2014-33282.M. Yu, W. Chen, R. Kania, G.V. Boven, J. Been. Underload induced crack growth behavior of minor cycles of pipeline steel in near-neutral pH environment. Fatigue & Fracture of Engineering Materials & Structures, Vol. 38, Issue 6, June 2015, pp.: 681-692.M. Yu, X. Xing, H. Zhang, J. Zhao, R. Eadie, W. Chen, J. Been, G.V. Boven and R. Kania. Corrosion fatigue crack growth behaviour of pipeline steel under underload-type variable amplitude loading schemes. Acta Materialia (considered for publication).Mengshan Yu, Weixing Chen, Richard Kania, Greg Van Boven, Jenny Been. Crack propagation of pipeline steel exposed to a near-neutral pH environment under variable pressure fluctuations. Submitted to International Journal of Fatigue for publication (under review).

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