Shooting led to event that moved pipeline; shift 150 miles from bullet hole wasn’t detected for months
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Allen Baker
A pipeline shift near Pump Station 5 was a result of maneuvers to drain oil from the trans-Alaska oil pipeline after it was punctured by a bullet, according to engineers with Alyeska Pipeline Service Co.
While the 13-inch movement wasn’t detected until four months after the bullet pierced the line on Oct. 4, the pipeline systems did their job, regulators agree.
Nine of the “honeycomb” anchors that absorb energy when the pipeline moves had to be replaced. The job took about six days.
“All of the movement systems that are on TAPS worked just great,” said Rhea DoBosh of the Joint Pipeline Office. “It moved, but the absorbers and saddles and all of the portions of the pipeline that are supposed to move worked well.”
The delay in spotting the movement does raise some questions, however.
“Should some other major event have happened, could it have caused some damage?” she said regulators are wondering. “If it was that major, should it have been detected earlier? These are things we are asking, and looking at in depth.”
The JPO, which includes federal and state regulators, has been looking at what level of surveillance is needed on the line, and this incident will be part of that larger review of “reliability centered maintenance,” she said.
The pipe moved as a result of forces from oil moving upstream when engineers were getting ready to drain oil out of the northern part of the line in the wake of the bullet piercing, according to Mike Heatwole of Alyeska.
When five relief valves at Pump Station 5 were opened, the oil flow from the south reached a rate of more than 1.2 million barrels daily as it surged downhill toward check valve 50, which is about a mile south of Pump Station 5. The valve is designed to close when just such a reverse-flow situation occurs, and it did, halting the flow. The momentum of the oil pushed the valve and adjacent piping 13 inches, crushing the energy absorbers mounted on the anchors.
There was no damage to the pipe, and engineers weren’t even aware of the incident until a ground surveillance crew on a routine inspection noticed it Jan. 4, Heatwole said.
Crews replaced the anchors and used hydraulic jacks to move the pipeline back into its regular position, he said.
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