Fatigue Damage Calculations for a Dented and Ovalled Section of the TransAlaska Pipeline System at Thompson Pass

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.