BP's old bugaboo, corrosion, might have struck again in the giant Prudhoe Bay oil field.
The oil company suspects corrosion contributed to a pressurized natural gas pipeline blowing apart on Sept. 29, BP spokesman Steve Rinehart said.
No one was hurt, though some workers were in the vicinity when the line ruptured violently, hurling a length of pipe across the tundra.
Automated safety systems and field workers rushed to shut down the pipeline, which was 8 inches in diameter and carried gas for shooting underground, part of a technique to help coax out additional crude oil.
The incident forced the shutdown of two well pads producing about 5,000 barrels of oil per day -- less than 1 percent of total North Slope oil output. The pads remained out of service on Friday.
BP will do a metallurgical analysis of the failed pipe before declaring corrosion as the culprit for the rupture, Rinehart said. Some possibilities have been ruled out, he said, such as a bad weld.
Investigators found the corrosion had attacked the outside surface of the above-ground pipe at a point where insulation that normally jackets the line was missing, Rinehart said.
Moisture had wicked beneath the exposed insulation and come into contact with the steel, causing corrosion that can eat through metal and weaken a pipeline, he said.
As a safety measure, BP workers will look for any pipes that might be in a similar condition, Rinehart said.
State and federal pipeline regulators are investigating the pipeline rupture.
BP runs Prudhoe, the nation's largest oil field, on behalf of itself and other owners including Conoco Phillips and Exxon Mobil.
Corrosion has bedeviled BP since 2006, when oil leaks from major Prudhoe pipelines drew intense regulatory and congressional scrutiny of the London-based company. The lines were found to be riddled with corrosion.
The leaks ultimately forced BP's Alaska subsidiary to plead guilty to a federal misdemeanor pollution crime. A judge put the company on probation for three years and imposed $20 million in penalties.
BP executives acknowledged lapses in pipeline maintenance, but since have said the company is investing hundreds of millions of dollars to replace miles of bad pipelines and improve upkeep.
Corrosion is a common industrial threat and a constant worry at Prudhoe with its vast maze of pipelines and processing plants that have been producing oil since 1977.
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