It is commonly believed that bending and other secondary loading will reduce the rupture pressure of a corroded pipe. This paper shows through theory, full-scale tests and finite element analysis (FEA) that this need not be the case in the field where displacement controlled bending and axial loading are induced by differential settlement and axial constraint. Based on this result, a new strain-based rupture prediction model is developed for buried corroded pipes subjected to internal pressure, lateral bending, thermal loading and residual stress. The selection of an appropriate “bulging factor,” the determination of a biaxial strain limit and the treatment of the heat affected zone (HAZ) are also discussed in the paper. The predicted rupture pressures agree well with the full-scale test results.
During the summer of 1996, the TransAlaska Pipeline System (TAPS) experienced vibrations in a section of the pipeline near Thompson Pass, north of Valdez, Alaska. Alyeska Pipeline Service Company, operator of TAPS, initiated an extensive investigation, and determined that the vibrations were caused by pressure pulses originating near a slackline-packline interface. The pressure pulses are thought to have been caused by the collapse of vapor bubbles trapped in the flow. The vibrations occurred only when the interface was positioned near a terraced portion of the pipeline topography on the downstream side of the pass. This knowledge allowed Alyeska Pipeline to control the vibrations by back-pressuring the pipeline to move the slackline-packline interface well above the terrace location.
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