FAIRBANKS - BP Exploration (Alaska) Inc. is drafting a response to two Democratic congressmen who have questioned past inspections of a recently discovered leaky pipeline on the North Slope, and the amount of solid material found in that line.
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Reps. John Dingell of Michigan and George Miller of California thanked BP's president, Steve Marshall, for meeting with their staffs in mid-March. But in a letter March 24, the congressmen said there were unanswered questions about the line's history and the cause of the spill.
The more than 200,000 gallons leaked was the largest spill ever on the North Slope, the congressmen said.
The "leading explanation appears to be corrosion," Dingell and Miller said.
Daren Beaudo, BP spokesman in Alaska, said Friday the leak investigation is not finished.
"We haven't come to a conclusion yet as to whether there was a cause or multiple contributing causes," he said.
The congressmen said BP's Marshall and his staff told them the line had been tested with ultrasound within the past six months and the pipe thickness was "within tolerance."
"While we applaud such testing, we still remain unclear where such tests were taken and whether such tests were made on the section that ultimately failed," they said.
BP reported that the pipe was last tested with a "smart pig" in 1998, the congressmen said.
A smart pig, which runs inside the pipe, maps the condition of the entire section through which it moves. The company then looks at specific locations with an ultrasound machine.
"We go back and go over spots that may have some corrosion tendencies," Beaudo said.
BP's corrosion management plan checks about 100,000 inspection points a year, he said. The company in the past has replaced lines because of corrosion.
The line that leaked carries about 15 percent viscous oil, Beaudo said. Viscous oil holds more solids than standard light oil, he said, and makes the line unique on the North Slope.
"We haven't had the same kind of issue with other crude transfer lines," he said.
Dingell and Miller asked why the line had not been "smart-pigged" since 1998.
They also asked detailed questions about solids in the line.
"It has been reported to us that the line in question, while having a low water cut, also has a very low flow rate and that this essentially makes the (oil transit line) a giant 'oil-water separator,"' the congressmen said. "We are advised that this results in the settlement of solids in the underlying layer of stagnant water. Is this the case? If so, what are the implications of this?"
The congressmen noted that the leak occurred near a caribou crossing where the line dips underground. They asked if solids collect in such locations. If so, they asked, could a maintenance pig have removed them.
The congressmen asked for a response by Monday.