NEW YORK (Reuters) - A risk assessment of the Trans Alaska Pipeline System in 2008 recommended replacing a stretch of line that leaked this month, since a concrete casing made it impossible to inspect for corrosion, operator Alyeska told a U.S. lawmaker this week.
A leak discovered on January 8 in a concrete-encased booster line along TAPS forced the 800-mile (1,287-km) pipeline system to shut last week, temporarily cutting off 12 percent of U.S. oil production, and forcing a risky winter-time repair. The pipeline restarted on Monday.
The last corrosion inspection on the leaky stretch of line occurred in 2008 but was deemed too risky and halted, operator Alyeska told Rep. Ed Markey, the ranking Democrat in the House Natural Resources Committee, in a letter dated January 18 and given to Reuters on Friday.
"Attempts to inspect the below ground concrete encased piping were stopped in 2008 due to the risk of potential damage to the piping during necessary removal of the concrete encasement," Alyeska CEO Thomas Barrett wrote.
"A risk assessment completed in October 2008 recommended not removing the concrete, but rather, replacing the pipeline."
Alyeska said it had planned to replace the stretch of pipe in question as early as this year. In 2009, Alyeska began the design and engineering work needed before replacing the stretch, said spokeswoman Michelle Egan.
"There has been progress made. The work that was required has begun," she said.
But Markey's office questioned the plans' pace.
"Despite a risk assessment .... which concluded that the pipe be replaced, that action has not yet even begun," Markey's office said in an email to Reuters.
Corrosion has plagued Alaskan pipeline infrastructure in the past, causing a number of past shutdowns and spills. It could take months to excavate the booster line and determine whether corrosion caused the most recent leak.
Alyeska is owned by the companies that operate on Alaska's North Slope -- BP owns about 47 percent of the venture, while ConocoPhillips and Exxon Mobil hold 28 percent and 20 percent respectively
Alyeska's letter to Markey also shows that oil had spilled from the TAPS line at least 20 different times since 2001. The total volume of oil spilled from TAPS over the period was 397,645 gallons (9,467 barrels), a chart provided to Markey and later sent to Reuters showed.
This month's leak on TAPS measured 317 barrels and shut down the pipeline for much of last week, forcing workers to brave harsh winter conditions to install a bypass pipe around the leak.
The incident shut in at least 4.6 million barrels of oil production, and helped push oil prices to gains of more than 4 percent during the three trading days after the leak was discovered.
Markey also questioned whether Alyeska has an effective leak detection system in place.
The letter shows this month's leak occurred "outside of the TAPS leak detection system, and was detected while someone was merely walking by on 'operator rounds'" Markey's office said. "This may indicate a lower level of leak detection systems than acceptable, especially at a key weak-point in the system."
(Editing by Marguerita Choy and Sofina Mirza-Reid)