In the Field
Routine surveillance identifies needed valve stem repair

Trans Alaska Pipeline System workers repaired a minor check valve stem leak after a routine maintenance inspection revealed a problem near Pump Station 12.

The leak was stopped almost immediately and no oil reached the environment. Workers monitored the valve after the initial repair and determined that a permanent repair was warranted.

Check valves are one-way valves located at strategic points along the pipeline to stop and isolate the flow of oil. They are important safety mechanisms that are held open by the forward flow of oil and close to limit the potential spill size if a leak causes a drop in oil pressure.

“Pipeline managers determined that some preventive action was necessary because of the valve’s sensitive location near the south bank of the Gulkana River,” said Randy Smith, Alyeska Pipeline Service Company’s central maintenance manager. Smith said evidence indicates that a hydraulic surge event on the pipeline in January forced crude oil and Drag Reducing Agent past Check Valve 99’s clapper shaft seals.

Alyeska administered a “mini shutdown” that stopped the flow of oil for about three hours on April 28 to repair the valve.

“The shutdown reduced line pressure to an acceptable rate to insure worker safety,” said Smith. “Draining the crude from the actuator followed by regular monitoring determined the crude leak was not an ongoing problem but more likely a onetime event,” said Smith.

Neither North Slope production nor Valdez tanker loading were affected by the shutdown. The 800 mile-long pipeline transports nearly one million barrels of oil per day from Prudhoe Bay to tankers in Valdez.