Effect of precyclic loading on stress-corrosion-cracking initiation in an X-65 pipeline steel exposed to near-neutral pH soil environment |
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Authors: | W Chen S -H Wang R Chu F King T R Jack R R Fessler |
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Affiliation: | (1) Present address: the Department of Chemical and Materials Engineering, University of Alberta, T6G 2G6 Edmonton, AB, Canada;(2) Integrated Manufacturing Technology Institute, National Research Council of Canada, London, Ontario;(3) Institute of Metal Research, 110016 Shengyang, China;(4) Environment and Corrosion Department, the Nova Research and Technology Corporation, T2E 7K7 Calgary, AB, Canada;(5) Biztek Consulting Inc., 60201-1724 Evanston, IL |
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Abstract: | A study was carried out to understand the effect of precyclic loading on stress-corrosion-crack initiation in an X-65 pipeline
steel exposed to a near-neutral-pH soil environment. The test specimens were precyclically loaded before corrosion exposure
to represent a service history of up to about 20 years, depending on the severity of pressure fluctuation. Microcracks had
initiated on the polished surface of the X-65 pipeline steel after long-time exposure at open-circuit potential (OCP) in a
near-neutral-pH synthetic soil solution. These microcracks were mostly initiated from pits at metallurgical discontinuities
such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed
along planes of the banded structures in the steel. The selective corrosion attack at these metallurgical discontinuities
is attributed to the galvanic nature of those areas to their neighbors. Cyclic loading prior to corrosion exposure had significant
effects on microcrack initiation and propagation during subsequent corrosion exposure. Cyclic loading prior to corrosion exposure
either reduced or increased the probability of crack initiation and the rate of crack propagation, depending upon the magnitude
of the stress cycles. The largest reduction was seen at a peak cyclic stress of about 0.8 of the yield strength. This cyclic-loading-dependent
cracking behavior might be related to the alteration of the substructures and the residual stress in the steel as a result
of precyclic loading. |
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