Effect of Dent Depth on the Burst Pressure of NPS30 X70 Pipes With Dent-Crack Defect

Published on Dec 9, 2014
· DOI :10.1115/IPC2014-33071
Hossein Ghaednia9
Estimated H-index: 9
(U of W: University of Windsor),
Sreekanta Das13
Estimated H-index: 13
(U of W: University of Windsor)
+ 1 AuthorsRichard Kania4
Estimated H-index: 4
Pipeline is the common mode for transporting oil, gas, and various petroleum products. Buried linepipe can be exposed to various external interferences and corrosive environment and as a result, damage in the form of dent or corrosion or crack or gouge or combination of any of these damages can form in the pipe wall. Such damage or combined damages can reduce the pressure capacity of the pipeline. A defect combining dent and crack, often known as dent-crack defect, can develop in the wall of a buried oil and gas linepipe. This combined defect may lead to a leak or a rupture in the pipe wall and hence, the pipeline operator becomes concerned about the performance and safety of the pipeline when a dent-crack defect is detected in the field pipeline. A long-term research program is currently underway at the Centre for Engineering Research in Pipelines, University of Windsor to study the influence of various parameters such as dent depth and operating line pressure on the pressure capacity or burst strength of 30 inch diameter and X70 grade pipes with D/t of about 90. From the study completed so far, it has been found that the dent depth of 8% with crack depth of 4 mm or more can reduce the pressure capacity by 32%. This paper discusses the test specimens, test setup, test procedure, test results, and data obtained from finite element analyses. INTRODUCTION Steel pipelines are the primary mode of transporting natural gas, crude oil, and various petroleum products in North America. In Canada alone, more than 110,000 km of buried energy transmission pipelines are in operation [1]. Damages or defects resulting from third party interference, more commonly known as mechanical damages are serious threat to the structural integrity of buried pipeline. Corrosion, crack, puncture, dent, gouge, and combination of such damages are some common examples of mechanical damage in pipelines. Mechanical damage of oil and gas pipelines is believed to be the major cause of failure of pipelines in service, and this damage may result in loss of product, explosions, fire, human and/or animal casualties, and pollution. It has been reported that the failure of oil and gas transmission pipelines resulting from mechanical damages ranges from 55% in the USA to around 70% in Europe [2-5]. Incidents of accidental impacts are not uncommon in onshore and offshore pipelines. Construction and excavation equipment can accidently impact the field pipeline causing mechanical damages such as dent and/or gouge with or without cracks. A dent is an inward permanent deformation in the pipe wall which causes a gross distortion of the pipe cross section [6]. A dent also causes stress and strain concentrations, ovalization, and a local reduction in the pipe diameter. A gouge is a metal loss defect that occurs in the pipe wall due to the scraping action of the excavating equipment or due to the rubbing action of the pipeline with a foreign object such as rock. Crack can also develop in a dent or gouge as a result of impact action or because of exposure to the corrosive environment or due to fatigue loading arising from pressure fluctuation and/or geotechnical movements [7]. Dent defects in energy pipeline have been a concern for pipeline operators. As a result, several research works were completed to understand the behavior of plain-smooth dents [8,
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