ANCHORAGE, AK – MARCH 30, 2000 – Because of renewed concerns brought to his attention by several employees in recent weeks, Alyeska Pipeline Service Company President Bob Malone is reiterating that pressure pulses in the pipeline near Thompson Pass pose no threat to the structural integrity of the pipeline.

The employees raised their concerns after the back-pressure control system used to eliminate the pulses was taken off line for three weeks starting January 31, when a “pig” used to clean the inside of the pipe broke up.

The pulses are caused by a slackline condition in the pipeline as it runs down the south side of Thompson Pass, north of Valdez. When faster moving oil at the top of the pass hits slower moving oil at the bottom, it causes turbulence, much like a waterfall hitting a pool of water below. The turbulence causes bubbles in the oil which sometimes travel down the line before collapsing, causing pulses, or brief vibrations in the pipeline. As throughput in the pipeline has declined in recent years, the slack line interface (surface of the pool) has moved farther down the pass, causing vibrations that could be felt by residents in the Heiden View subdivision. In 1997, Alyeska installed a back pressure control system at the Valdez Marine Terminal, effectively pushing the pool being hit by the waterfall back up the mountain, reducing the turbulence and eliminating the pulses.

Previous inspection of the pipe in that area had detected a dent and ovality that had been caused during construction of the pipeline. To determine whether the pulses were reducing the fatigue life of the pipe in the area of the dent, Alyeska hired consultants who did extensive computer analysis and determined that with the back pressure control system, the fatigue life of the pipe would be over 63 years. And it showed that occasionally operating without back pressure control, even for periods of up to a month, do not significantly affect fatigue life.

Alyeska will analyze the effect of the pulsations on much smaller anomalies in the same area to determine a fatigue life. That analysis is being done by the same consultants and is expected to take several weeks. The results will be provided to the Joint Pipeline Office.

The employees have also raised concerns about the effect of the pulses on Remote Gate Valves and Check Valves in that area of the pipeline. The valves were designed to withstand major seismic activity, far greater than the vibrations that were occurring at Thompson Pass.

Malone said, “We appreciate the employees who raised these concerns, and we take them seriously. We are confident in the findings of the initial study and expect this further study will confirm our view that these pulses pose no threat to the integrity of the pipeline.”

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