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Timms, Chris M.J. (C-FER Technologies Edmonton, Alberta, Canada) | DeGeer, Duane D. (C-FER Technologies Edmonton, Alberta, Canada) | Chebaro, Mohamed R. (C-FER Technologies Edmonton, Alberta, Canada) | Tsuru, Y. (Nippon Steel Corporation Futtsu City, Chiba-Ken, Japan)
For arctic pipeline systems, designers are required to deal with a number of unique environmental loading conditions not normally present in other regions of the world. For buried arctic onshore pipelines, the key structural design issue is the potential for high bending strains resulting from permafrost: frost heave and/or thaw settlement. Because of the lack of traditional design solutions to these unique deformation-controlled loading conditions, reliability-based limit state design methods are becoming increasingly preferred for arctic applications. They allow the integration of analytical and experimental assessments into the overall design philosophy, which has been shown to improve design concept confidence and reduce overall uncertainty. For a strain-based design approach, high pipeline bending strains due to deformation-controlled ground movements are addressed as a function of the defined allowable tensile and compressive strain limits. Excessive compressive strains may give rise to serviceability issues such as restricted pipeline pig passage or coating damage. In some cases, excessive compressive strains may compromise pipeline integrity due to other loads and could lead to ultimate limit state conditions associated with burst, fatigue or corrosion under damaged coating. To further develop the understanding of pipeline compressive strain capacity, this paper summarizes a test program performed at the C-FER Technologies (1999) Inc. (C-FER) testing facility in Edmonton, Canada, which quantified the critical compressive strain of 36-inch diameter, 19.8-mm wall thickness, grade X80 UOE linepipe. Test variables included heat treatment effects (simulated coating plant heating) and the presence of a girth weld. Work involved performing thermal treatment studies, material coupon tests and three full-scale bend tests on X80 UOE linepipe specimens subject to high internal pressure. As expected, the analysis of the results has shown that the presence of an offset in the girth weld reduced compressive strain capacity.
Varelis, George E. (Structural Integrity Department, Centro Sviluppo Materiali SpA) | Karamanos, Spyros A. (Department of Mechanical Engineering, University of Thessaly) | Gresnigt, A.M. (Department of Civil Engineering and Geosciences, Delft University of Technology)
Kawabata, Toshinori (Graduate School of Agricultural Science, Kobe University Kobe, Hyogo, Japan) | Hanazawa, Takafumi (Graduate School of Agricultural Science, Kobe University Kobe, Hyogo, Japan) | Kashiwagi, Ayumu (Graduate School of Agricultural Science, Kobe University Kobe, Hyogo, Japan) | Izumi, Akira (Graduate School of Agricultural Science, Kobe University Kobe, Hyogo, Japan) | Kanda, Motohiro (Graduate School of Agricultural Science, Kobe University Kobe, Hyogo, Japan) | Mohri, Yoshiyuki (National Research Institute for Rural Engineering Tsukuba, Ibaraki, Japan) | Shimura, Kazunobu (Hokuriku Regional Agricultural Administration Office, Maruoka, Sakai, Fukui, Japan)
Thrust force is generated at pipeline bends due to internal pressure. The thrust forces can induce joint separations of the pipelines. In Case of high internal pressure, effective methods for thrust restraint are required. Methods for thrust restraint using liquefied stabilized soil reinforced with geosynthetics are proposed in this paper. The behavior of the bens backfilled with liquefied stabilized soil is not cleared. We expect that the liquefied stabilized soil is an effective backfill material against the thrust force. In addition, the geosynthetics contributes to restrain the failure of the liquefied stabilized soil. In this paper, bending tests of the liquefied stabilized soil in order to verify the effect of the proposed methods for thrust restraint are discussed. The liquefied stabilized specimen was cured for 7 days in a mold having a length of 1000 mm, a width of 150 mm, and a depth of 150 mm. The geosynthetics were changed in various ways. After cured, the bending tests were carried out. The liquefied stabilized specimen was vertically loaded at 1 mm/min, using a jack to simulate the thrust force. The load and the vertical displacement of the loading plate were both measured. The results show that the bending stiffness in case using the liquefied stabilized soil with geosynthetics was increased. It is verified that the proposed method is extremely effective against thrust restraint.
Generally pipeline for irrigation is subjected to internal water pressure. In bend in such pressure pipeline, thrust force is generated depending on the pressure level and bending angle. This thrust force tends to move the bend of underground pipeline outward. Commonly, the thrust force is resisted by the passive resistance acting on the pipe bend. A concrete block is installed at the pipe bend when the thrust force is larger than the passive resistance. However, it is expected that such heavy concrete block becomes a weak point during earthquake because the concrete block moves largely due to inertia.
This paper addresses bending actions and curvature on pipelines that may occur accidentally due to external loads or ground movements for buried pipelines. The scenario is characterized by extreme plastic de-formations where tensile straining and stability issues (buckling) need to be considered. The structural pipe behaviour is estimated via analytic equations in an isotropic manner using von Mises plasticity. Analytically, limit values for bending actions or plastic strains are derived. The analyses are supported by a full-scale test on a pressurized HFI welded pipe of steel grade X70, accompanied by material testing, from which strain hardening properties were derived.