In the Field
Pipeline Support Members Being Repaired

As part of the ongoing maintenance of the Trans Alaska Pipeline System (TAPS), two vertical support members (VSMs) that are shifting vertically and laterally are being replaced at Jim River 2, near Pump Station 5. The project is slated for completion in 2007. There are 78,000 VSMs that support the above-ground pipeline sections throughout TAPS.

The two Jim River VSMs are moving toward a large “pingo,” which is a mound or hill of ice covered by an outer layer of soil. Pingos form because of permafrost and can range from the size of a car to as large as a dome sports stadium. If Jim River comes in contact with the nearby pingo, the river water will melt the inside ice core and the pipeline could move up to 30 feet, resulting from the buried core of ice lifting the soil as it expands. Two VSMs will be replaced. The replacements will be frozen into the ground at slightly different locations before the original VSMs are removed.

Approximately 420 miles of TAPS pipe rests on top of five-foot to 15-foot-tall VSMs that are designed to prevent pipeline heat from melting permafrost. This permanently frozen soil is found beneath about 75 percent of the pipeline corridor. These pipes contain anhydrous ammonia, which vaporizes at temperatures just below freezing, rises and condenses at radiators above ground when the air temperature is well below freezing. This process transfers ground heat into the air during cold periods, thereby lowering the ground temperature. “The VSM replacement project is simply one part of the constant effort to properly maintain this asset now and into the future,” Tom Coghill, Director of Alyeska Civil Projects and Programs said.