Effect of Backfill Temperatures on Axial Restraint of Pipelines
Publication: Journal of Pipeline Systems Engineering and Practice
Volume 12, Issue 3
Abstract
One consideration for pipeline design is the Delta-T. There may be a tendency to assume a conservative value for winter construction, the extreme value being the air temperature. In applying a low restraint temperature in winter, the Delta-T is increased. The consequence of an artificially high Delta-T is that the pipeline may notionally experience high stresses; in extreme cases, mitigation is required to counteract these stresses. In winter, the soil at pipeline depth will usually be unfrozen or slightly frozen. When a pipeline nominally at ambient air temperature is backfilled, the warmer backfill soil will quickly warm the pipeline steel from the air temperature to a more moderate temperature. As a result, the pipeline is unlikely to attain full axial restraint at low air temperatures but instead at more temperate temperatures. In contrast, for pipelines constructed in summer and assumed to be backfilled at warm air temperatures, the resulting Delta-T may be nonconservative, particularly for hot pipelines. This paper presents the test results for several pipelines installed in winter and summer. The pipelines were instrumented with thermistors to monitor pipeline and soil temperatures and strain gauges to monitor pipeline strains during the backfilling process. Guidance is provided as to appropriate tie-in temperatures.
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Data Availability Statement
Some or all data generated or used during the study are proprietary or confidential in nature and may only be provided with restrictions.
Acknowledgments
The authors thank the project sponsor, Inter Pipeline, for funding these studies and for granting permission to publish these data.
References
ASME. 2016a. Gas transmission and distribution piping systems. ASME B31.8. New York: ASME.
ASME. 2016b. Pipeline transportation systems for liquids and slurries. ASME B31.4. New York: ASME.
CSA (Canadian Standards Association). 2015. Oil and gas pipeline systems. CAN/CSA-Z662. Rexdale, ON: CSA.
CSA (Canadian Standards Association). 2019. Oil and gas pipeline systems. CAN/CSA-Z662. Rexdale, ON: CSA.
McAffee, R., R. Phillips, and M. Martens. 2014. “Field testing of pipeline trench backfill properties placed during winter conditions.” In Proc., 67th Canadian Geotechnical Conf. Regina Saskatchewan. Richmond, BC: Canadian Geotechnical Society.
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© 2021 American Society of Civil Engineers.
History
Received: Jul 1, 2020
Accepted: Jan 20, 2021
Published online: Apr 19, 2021
Published in print: Aug 1, 2021
Discussion open until: Sep 19, 2021
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