ANCHORAGE - An aggressive cleaning device sent through the trans-Alaska oil pipeline failed to find a 20-inch diameter metal ring that went missing in the line in December, a spokesman for the operator said Sunday.
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The stainless steel ring is part of another cleaning tool called a scraping pig that broke apart inside the 800-mile line. A later scraping pig pushed out other missing pieces. The pigs are run every seven to 14 days.
The cleanings removed wax buildup from the pipeline's 48-inch diameter walls, but they failed to turn up the ring. On Saturday Alyeska Pipeline Service Co., the pipeline operator, ran a more aggressive device called a disc pig through the line.
The device scraped out enough wax to fill 11 55-gallon drums, but also failed to find the ring, said Mike Heatwole, an Alyeska spokesman.
"We'll just keep looking," he said.
Now Alyeska plans to strain the paraffin collected earlier to see if the missing part is there. The paraffin is currently on a barge heading south for processing. The barge is expected to arrive in Seattle in late February.
"Results are not expected for as much as two months from now," Heatwole said.
Alyeska has downplayed the risk, saying there is a low probability that the ring would interfere with a check valve that stops the flow of oil in the case of a leak.
Meanwhile, cleaning pigs will be run through the pipeline every five days in preparation for an inspection with a "smart pig," a device that assess the condition of the pipeline.
Smart pigs usually are employed every three years. But Alyeska moved the schedule up by a year after a March 2006 spill from a leaking feeder line at Prudhoe Bay, the nation's largest oil field and the North Slope starting point of the trans-Alaska pipeline.
Alyeska launched the smart pig just before more leaks were discovered at Prudhoe in August, prompting a partial shutdown of the field. But the completion of the inspection was later put on hold after Alyeska found data collected was compromised by excessive wax buildup south of a pump station about 200 miles from the north end of the pipeline, Heatwole said.
The job will be resumed in late February or early March, he said.