BP has closed the largest oilfield in the United States, which provides 8 percent of US oil, after a robot discovered extensive corrosion within a transit pipe connected to the main Alaska Pipeline. The US Pipeline and Hazardous Materials Safety Administration ordered BP to send in a robot to inspect the pipe visually after a 201,000 gallon spill of crude onto the Alaskan tundra in March. BP initially did only random testing with ultrasonic sensors. The robot, called a Smart Pig, discovered 16 weakened areas within the pipe. BP will have to replace 16 miles of pipe and the resulting outage may last several months. The robot, which is designed to inspect the pipeline for just such corrosion, had not been used by BP since 1992. Federal regulators said the robot should have been inspecting the pipeline much more often. BP has been under pressure for several months to improve its pipeline maintanence and inspection procedures. BP's problems prompted an exchange between a US Congressman and PHMSA officials (PDF format) which suggests BP allowed so much sludge to build up in the pipes that it became impossible for the Smart Pig robot to travel through them. Some journalists think there may also be darker motives to BP's timing reminiscent of Enron.