Alyeska investigates shifting of pipeline

Posted: Wednesday, May 17, 2000

ANCHORAGE (AP) -- A mile-and-a-half section of the 800-mile trans-Alaska oil pipeline has abruptly shifted south, shearing bolts that hold the pipe to supports.

The pipeline moved between 3 and 6 inches on the section south of the Brooks Range, said Tim Woolston, spokesman for Alyeska Pipeline Service Co., which runs the pipeline. The problem was discovered Monday.

As designed, the bolts that hold the pipe to supports sheared off, allowing the pipe to move without breaking.

''Everything worked as designed,'' Woolston said. ''Now, we're all very curious about why this happened.''

The pipeline shift happened on the south side of Atigun Pass, where the pipeline levels off after the steep descent from the 4,739-foot pass that cuts through the Brooks Range.

Engineers have not determined what caused the shift. But unique conditions created by oil falling steeply from the pass have caused the pipe to shudder and vibrate in the past and will be examined, Woolston said.

The shift poses no immediate risk to the strength of the pipe and the flow has not been affected, Woolston said.

Alyeska says the pipe has never shifted off its supports since start-up in 1977. However, a similar incident happened during a test before start-up, Woolston said.

The pipeline is buried for about half its length, and 78,000 supports prop up the pipe where it runs above ground. The pipeline is designed to adsorb shifts due to earthquakes and other forces.

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