Solutions for the steady state, quasi-static buckle propagation pressure in corroded pipelines have been derived analytically and compared to finite dement predictions (ABAQUS). The corroded pipeline was modeled as an infinitely long, cylindrical shell with nonuniform thickness. A section of reduced thickness was used to describe the corroded region, with angular extent β and depth d. The pipeline was assumed to be rigid, perfectly plastic and a four plastic hinge mechanism is used to describe plastic collapse. The locations of the plastic hinges were found to depend on the amount of corrosion. When β< 90°, the propagation pressure decreased rapidly with increasing values of both fl and d/t, but only within a specified range of values for the corrosion depth. Outside of this range, the propagation pressure was independent of fl and decreased less rapidly with increasing corrosion depth. When β > 90°, the propagation pressure depended only on the corrosion depth and a parametric study showed that the propagation pressure decreased monotonically as the corrosion depth increased. The rigid-plastic solution based on the four plastic hinge collapse mechanisms provided fairly good predictions of buckle propagation pressures when the corrosion depth was within 50% of the pipeline thickness.
Pipelines that transport oil and natural gas from deep ocean wells are designed to withstand very high hydrostatic pressure. For every 100 m, the external hydrostatic pressure increases roughly 1 MPa. Sometimes these pipelines may develop a local buckle due to accidental collisions by anchors or drill collars. If the hydrostatic pressure is high enough, the buckle will propagate along the pipeline, flattening the pipeline in a dog-bone shape as shown in Fig. 1 (Chater and Hutchinson, 1984). In between the buckled and unbuckled regions of Fig. 1 is the transition zone.
