Influence of Pipeline Misalignment on the Local Buckling Response

Pipeline transportation systems are generally constructed by connecting individual linepipe segments through joint-to-joint end girth welds. The mechanical behavior of shell structures, such as a pipeline, can be sensitive to initial imperfections in geometry, material properties and loading. These initial imperfections can affect the pipeline load-deformation response and reduce the limit moment and strain capacity. Initial geometric imperfections may result from fabrication processes, as related to variations in the pipeline diameter and wall thickness. These geometric imperfections may have circumferential and longitudinal variation. During the construction process, the initial geometric imperfections may be the result of end misalignment due to longitudinal pipeline offset and ovality. This study examines the influence of initial geometric imperfections associated with joint-to-joint misalignment that may be present due to the girth welding process when connecting pipeline segments. A parametric analysis was conducted using finite element methods to assess the effects of diameter-to-wall thickness ratio, internal pressure, axial force, misalignment amplitude, and misalignment orientation, on the local buckling response of pipelines. Through this parametric analysis, the moment-curvature response, variation in section geometry with increasing curvature, limit moment and strain capacity were all examined. Comparison of the results with those obtained from the engineering codes and recommended practice is also presented. This study concludes that offset misalignment orientation, with respect to the bending axis, and the increasing misalignment imperfection amplitude both affect the pipeline peak moment and global strain capacity at the limit moment.