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Permanent link (DOI): https://doi.org/10.7939/R37W67H1C

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Growth behavior of surface cracks in pipeline steels exposed to near-neutral pH environments Open Access

Descriptions

Other title
Subject/Keyword
corrosion
Stress corrosion cracking
corrosion-fatigue
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Egbewande, Afolabi T.
Supervisor and department
Weixing Chen (Chemical and Materials Engineering)
Examining committee member and department
Samer Adeeb (Civil Engineering)
Reg Eadie (Chemical and Materials Engineering)
Bill Tyson (CANMET, ottawa)
Barry Wiskel (Chemical and Materials Engineering)
Department
Department of Chemical and Materials Engineering
Specialization
Materials Engineering
Date accepted
2013-10-07T09:00:46Z
Graduation date
2013-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
This study is part of a larger study designed to help a consortium of pipeline operators replace current (very expensive) approaches to managing stress corrosion cracking (SCC) concerns in near-neutral pH (NNPH) environments with mathematical models that predict SCC growth rates. This could significantly reduce the cost of pipeline integrity management programs. The goal was to help find ways to improve the accuracy of existing models. NNPHSCC cracks are surface-type flaws. However, NNPHSCC was typically modelled as through-thickness cracks in previous laboratory studies. This was identified as a major reason why current NNPHSCC models are inaccurate. Therefore, this study was designed to model NNPHSCC cracks as surface-type flaws rather than through-thickness cracks. Results showed contrary to popular opinion that surface-type flaws propagated less rapidly than through-thickness cracks in NNPHSCC environments. Also, inherent variations in the local environment under a disbondment produce hydrogen concentration gradients that result in very high propagation rates at the open mouth of a disbondment. The propagation rate declines very sharply non-linearly distance away from the open mouth inside the disbondment. It was determined the environmental factor used to account for the contribution of the environment to crack propagation, could be up to ten times higher at the open mouth compared to other locations under the disbondment. Identifying these issues helps to guide NNPHSCC modellers in selecting more appropriate growth rates for SCC programs. A series of propagation rate ranges under various environmental and mechanical loading conditions were determined. Contrary to popular opinions, increased CO2 concentration in groundwater decreased crack propagation rates by intensifying (environmental) crack tip blunting. This delayed crack re-initiation from a dormant state. Under benign loading conditions, this helps to reduce/stop iv crack growth by driving towards dormancy. Mechanically blunting a crack tip was found to produce the same effect. Hydrogen enhanced localized plasticity (also called hydrogen enhanced low temperature creep) was found to be responsible for this blunting effect. Means of manipulating the mechanical loading factors to produce this effect were identified.
Language
English
DOI
doi:10.7939/R37W67H1C
Rights
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. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. 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.
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