2nd pipeline shutdown slated for the weekend 36 HOURS: Workers set to install new piping to fix leak.

The trans-Alaska pipeline is scheduled to shut down again this weekend for about 36 hours while workers install new piping to fix a leak that prompted a four-day emergency shutdown, company officials and regulators said.

The 800-mile line restarted at reduced flow on a short-term basis Tuesday night. The line was carrying oil from the North Slope oil fields on Wednesday at about two-thirds of its normal rate: roughly 400,000 barrels per day.

Federal and state regulators are allowing Alyeska Pipeline Service Co. to pump oil through the line even though it is causing more oil to leak from the faulty pipe encased in concrete at Pump Station 1 that prompted the shutdown on Saturday.

The ranking Democrat on the U.S. House Natural Resources Committee sent a letter to Alyeska on Wednesday with a battery of questions about the leak -- why it happened and whether the decision to restart the 800-mile line has created new spill risks.

Rep. Edward Markey of Massachusetts reminded Alyeska in his letter that the company testified to Congress in 2007 that accelerated corrosion was not a threat for the 800-mile line. The company also testified that it had added new corrosion monitoring locations at Pump Station 1, he wrote.

"It would appear those new monitoring locations were insufficient," Markey wrote. He requested a response to his letter by next Tuesday.

At this time, regulators and company officials have not said whether the leak, which spilled hundreds of gallons of oil into the basement of a building at Pump Station 1, was caused by corrosion. Alyeska said it needs to excavate the line to know for certain.

Alyeska said Wednesday night that it did a risk assessment on concrete-encased piping at the pump station in 2008. The company did not share the results of the risk assessment but said it replaced some concrete-encased piping at the pump station last year. Planning for a project to replace the buried line that is leaking began in 2009 but work wasn't scheduled to begin this until year, with completion in 2013.

Public records show that federal regulators in the past decade have required Alyeska to improve its corrosion detection at Pump Station 1 and replace an aging line that carried most of the oil from the North Slope to the pump station. That line was replaced in December, according to BP.

SMOOTH RESTART

As temperatures dropped at Prudhoe Bay and the shutdown of the pipeline continued into its fourth day on Tuesday, regulators agreed with Alyeska that restarting the flow of oil would reduce the risk of even bigger problems for the pipeline.

Restarting the pipeline was expected to raise the temperature of oil in pipelines and tanks, avoid a more complex cold restart, avoid potentially serious problems with freezing and wax buildup and allow North Slope operators to resume higher levels of production, Alyeska said.

On Wednesday, at least 500 people -- state, federal and company workers -- were working on major tasks related to the restart and the shutdown coming this weekend. Many of them were stationed along the pipeline to watch for possible problems -- new leaks, for example -- that might sprout as the company restarted the chilled pipeline. As of Wednesday night, Alyeska officials said no new leaks had been detected.

Alyeska spokeswoman Michelle Egan said Wednesday that the restart has been "very smooth," and the additional oil that has leaked at Pump Station 1 has been captured in an 800-gallon vault installed for that purpose.

On Wednesday, oil was leaking from the pipe and into the vault at a rate of about 1.8 gallons per minute, according to the federal Environmental Protection Agency.

State spill response coordinator Tom DeRuyter said the restart so far is going as planned. "The pipeline is under intense scrutiny right now," he said.

SECOND-LONGEST SHUTDOWN

Between 8 p.m. Tuesday and 4 p.m. Wednesday, about 2,310 gallons of oil were removed from the vault, company officials and regulators said in a joint statement.

The pipeline shutdown started about 9 a.m. Saturday and lasted about 84 hours, the second-longest shutdown in the pipeline's 33-year history.

Oil producers at the more than two dozen nearby oil fields had cut production from about 630,000 barrels a day to about 30,000, with that limited flow going into storage tanks that by Tuesday were filling up.

BP Alaska spokesman Steve Rinehart said he expects that the oil fields will be able to operate "at some level" during the upcoming pipeline shutdown.

"We are working closely with them to manage that," Egan said.

Find Elizabeth Bluemink online at adn.com/contact/ebluemink or call 257-4317.

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