Two full-scale tests on X52 grade NPS12 oil/gas pipeline show that this pipeline is able to maintain its integrity and does not rupture when subjected to monotonic bending deformation and moderate to high internal pressure. However, this kind of test is expensive and time consuming and thus, an alternative tool using finite element method was developed to study the behavior of wrinkled pipeline under similar load-deformation condition. This finite element model uses true nonlinear material and non-linear geometry. A special contact and sliding algorithm was used to model the folding and sliding behavior of the inside surfaces of the wrinkle. The finite element model was validated with the data obtained from the full-scale tests. A good agreement was obtained between the post-wrinkling behaviors obtained from the test and from the numerical analysis. This paper discusses the numerical modeling technique that was used in this study and the results obtained from the study.
North American oil and gas industry uses steel pipelines as the primary mode for transporting natural gas, crude oil, and various petroleum products. In Canada alone, about 700,000 km of oil/gas pipelines are in operation. Many additional pipelines projects especially in West Canada and Alaska of various scales such as Mackenzie Gas Project and Alaska Highway Pipeline are underway. The majority of these pipelines run below ground (Yukon Government, 2006). Field observations of buried oil/gas pipelines indicate that the subsurface geotechnical movements with or without thermal loads can introduce large forces and displacements on buried pipelines resulting in localized curvature, strains, and associated deformations in the pipe wall. Often the local deformations of the pipe wall results in local buckling of the pipe wall (called "wrinkling") and, in its post-buckling range of response, local buckles (wrinkles) in the pipe wall grow under sustained deformations.