A surveyor records results from a pipeline sonogram. Walls with less than 20 percent of their original thickness are flagged.
Operators of Alaska's giant Prudhoe Bay oil field scramble to inspect pipelines for signs of corrosion, as they try to decide whether it's safe to keep pumping oil from parts of the field.
BP has already shut down about half of Prudhoe Bay, after discovering a small oil spill last weekend, when about 630 gallons of crude oil leaked.
Alaska Gov. Frank Murkowski and other officials toured the Prudhoe Bay oil pipelines, which have been crippled by corrosion problems discovered this week. The threat of a stoppage also endangers Alaska's budget: Oil taxes account for more than 90 percent of its revenues.
For now, workers in hazmat suits have contained the oil in an area about one-quarter the size of a football field, where they're attempting to sponge the oil from the grassy tundra.
Prudhoe Bay is the largest U.S. oilfield, representing 8 percent of domestic production. BP, which controls the oil rights, began shutting down the western portion of the field after a small leak — and extensive corrosion — was found.
Before the shutdown, the Prudhoe Bay field had been producing 400,000 barrels of crude oil a day. BP has announced that it will try to maintain a diminished flow of oil from the field as it works to repair or replace some 16 miles of pipeline.
Located on Alaska's North Slope, the Prudhoe Bay oil field was discovered in 1968. It remains the largest oil field in North America.