Crews have quickly built temporary supports to replace damaged metal brackets supporting portions of the trans-Alaska Pipeline, while officials continue with a full systems check and integrity assessment in the wake of a Nov. 3 earthquake. The 800-mile pipeline was shut down but did not rupture, and no oil leaks have been reported.
"It's pretty early in the game and crews are still on the scene assessing damage," says Leslie Pearson, emergency response program manager for the Alaska Dept. of Environmental Conservation.
The 7.9 earthquake struck at 1:12 p.m. on Nov. 3, according to the Alaska Earthquake Information Center. The epicenter, located about 175 miles north of Anchorage and 40 miles east of Denali National Park, is on the Denali fault line at the relatively shallow depth of 3.1 miles. The quake ruptured eastward toward the pipeline.
The 48-in.-dia pipeline, which normally delivers about 1 million barrels of crude oil a day, is constructed to withstand an earthquake up to magnitude 8.5, depending on the location relative to known fault lines. Alyeska Pipeline Service Company, the consortium that operates the pipeline, reports the earthquake monitoring system performed as designed, automatically shutting down the system with management by the operations control center, says Marnie Isaacs, an Alyeska spokesperson.
The line was fully shut down within an hour after the quake. Helicopter crews began aerial surveillance while ground crews mobilized to begin inspection. The company prioritized 160 inspection action items covering a 200-mile stretch and completed 95 of them as of Nov. 5.
The earthquake damaged at least 13 metal H-brackets that support above-ground portions of the pipeline, which lies up to 18 ft deep in general. The damage is limited to a roughly 1-mile area around Mile 588. The crossbeams of the H structures collapsed, says Isaacs. Although the pipeline has its own rigidity, the lack of support caused it to sag in some places. Workers built temporary wooden support structures to relieve local stress on the pipeline.
So far, weather has not hampered the inspection, but about half of the pipeline is under ground in this area and will take longer to inspect. At press time, there was no word on when the pipeline would restart.