ANCHORAGE, AK -- August 6, 1998 -- Alyeska Pipeline Service Company reported today that a segment of the pipeline was overpressured due to human error during a re-start of Pump Station 9 yesterday afternoon. No damage to the pipeline has been found. A review and investigation of the incident is underway. A preliminary evaluation determined the pipeline was 124 percent of the maximum allowable operating pressure for approximately nine minutes. The pipeline is permitted to go up to 110 percent of maximum allowable operating pressure during a restart or upset condition.

At 11:50 a.m. yesterday, newly installed computer software misinterpreted the status of two Remote Gate Valves (RGVs) south of Pump Station 10, and concluded that the valves were not fully open. The computer responded as designed and immediately idled the nearest pump station to the north, Pump Station 9, and began closing the valves in the pipe segment south of Pump Station 10. The pump station was re-started while the RGVs south of Pump Station 10 were closing, which is counter to standard operating practice. The overpressure occurred when the pumps at Pump Station 9 began to move oil against the closing valves. Approximately four minutes after the RGVs started closing, Pump Station 9 was shutdown by the Pipeline Controller.

Aerial and ground surveillance of the pipe segment was completed and no indication of damage to the pipeline was found. Additional surveillance and analysis is planned. The incident is under investigation and a root cause analysis of the situation will be performed.

The maximum allowable operating pressure for a segment of pipe is 72 percent of the yield strength of the pipe, giving a safety margin for pipeline operations. The pipeline is permitted to go up to 110 percent of maximum allowable operating pressure during a restart or upset condition, which corresponds to 79 percent of yield strength. Yield strength is defined as the point at which metal stretches and does not return to its original shape.

The Operations Control Center is located in Valdez and controls the operation of the pipeline and the Valdez Marine Terminal. Pump Station 9 is south of Delta Junction.

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