A device designed to clean waxy buildup from the walls of the 800-mile Alaska pipeline broke apart inside the pipeline in December, raising the possibility that any remaining shards of machinery might damage sensitive valves, an executive of Alyeska, the company that runs the pipeline, confirmed Thursday.
Most pieces of the broken cleaning device, known as a pig, were recovered in late December, according to an internal e-mail message from Jim F. Johnson, a vice president of Alyeska, but a large metallic ring has not been recovered. Mike Heatwole, a spokesman for Alyeska, confirmed the details in the message.
The pipeline was not shut down during the recovery operation, but, coming less than six months after supplies of Alaskan crude oil were temporarily cut in half after a leak in a feeder pipeline on the North Slope, the disintegration of the pig is a reminder of the maintenance challenges posed by the three-decade-old pipeline system and the increasingly sluggish rate at which the oil travels.
The loss of the device, called a scraper pig, ''is a concern, yeah,'' said Rhea DoBosh, the spokeswoman for the Joint Pipeline Office, a consortium of 12 state and federal agencies that have some jurisdiction over the pipeline. ''But,'' Ms. DoBosh said, ''they have found most of the parts. There's just that one piece remaining, and there's a lingering question of where it might be.''
She added, ''The hope is that this piece is not lodged some place that it's going to do any damage.''
Mr. Heatwole said such a failure was rare in the routine, biweekly practice of running maintenance pigs through the pipe.
''Somewhere along the line,'' he said, one device ''came apart.'' He said the device was designed to do that if it hit a blockage so a stuck pig would not shut down oil deliveries.
Pat Klinger, a spokeswoman for the Pipeline and Hazardous Materials Safety Administration at the Transportation Department, which has authority over the pipeline, said Thursday, ''We're concerned why this happened, and obviously there's a piece missing and we want to make sure that we all find that piece.''
The primary concern, for the pipeline's operators and its regulators, is that the remaining piece could interfere with the valves that control the flow of oil through the system that links the oilfields in northern Alaska with the Port of Valdez.
At a September Congressional hearing into the failure of a BP feeder line in the Prudhoe Bay area, both Republican and Democratic lawmakers held up Alyeska's maintenance program as an object lesson to BP, asking why, if pigs can be run through the 48-inch Alaska pipeline every two weeks, BP had waited years to perform similar maintenance, allowing sludge and sediment to build up and hastening corrosion.
But a letter sent this week to Representative John D. Dingell, Democrat of Michigan and the chairman of the Energy and Commerce Committee, noted that at about the same time Kevin Hostler, the president of Alyeska, was testifying before the committee, a ''smart'' pig, filled with electronic sensors that measure the thickness of pipeline walls, was making an unsuccessful run through the pipe. Committee staff members had no immediate comment on the letter.
The letter, sent by Charles Hamel, who has long been a conduit for worker complaints about management on the North Slope, particularly involving the fight against corrosion, said, and an Alyeska spokesman confirmed, that the ''smart'' pig had been unable to get any readings for most of its run.
A new run of a pig with electronic sensors is planned in a few weeks.
Mr. Heatwole of Alyeska said in an e-mail message that after the scraper pig disintegrated in the pipe in December, a second scraper pig picked up 40 barrels' worth of wax, along with the remnants of the broken pig. The missing ring, he said, was made of stainless steel and was 20 inches in diameter and one inch wide.
He added that, in a separate incident involving a six-inch bypass line, about 800 gallons of oil spilled last month at Atigun Pass in the Brooks Range of northern Alaska. Although there have been several spills in recent years in the network of feeder lines on the North Slope, which are not part of the Alyeska system, this month's spill was only the second on the large pipeline in the past five years. The last, in which 285,000 gallons were spilled, came after a bullet was fired into the pipe.
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