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The Trans-Alaska Pipeline System
, usually called the Alyeska Pipeline in Alaska or the Alaska Pipeline elsewhere, is a major U.S. oil pipeline connecting oil fields in Alaska's North Slope to a North Pacific seaport where the oil can be shipped to the Lower 48 states for refining.The main Trans-Alaska Pipeline runs north to south, almost 800 miles (1,300 km), from the Arctic Ocean at Prudhoe Bay, Alaska to the Gulf of Alaska at Valdez, Alaska, passing near several Alaskan villages and towns, including Wiseman (pop. 21), Bettles (pop.39), Livengood (pop.29), Fox (pop.300), Fairbanks (pop. 34,540), and Glennallen (pop.554)Oil emerges from the ground at up to 180 °F (80 °C), and travels through the pipeline at temperatures above 120 °F (50 °C). In some elevated portions, heat conduction from the oil through the Vertical Support Members (VSMs) would melt the permafrost in which the VSMs are embedded. This would cause the pipeline to sink and possibly sustain damage. To prevent this, these portions of the pipeline include heat exchangers atop each VSM, passively cooled by convection to the air. Each heat exchanger is thermally coupled by a heat pipe to the base of the VSM. Running through the VSM, the heat pipe transports heat from the base to the heat exchanger. Since ammonia, the working fluid in the heat pipes, has a freezing point lower than the permafrost, the heat pipe works throughout the year, even during the coldest winter nights. This convection cooling system is thought by TAPS engineers to be the greatest innovation associated with the pipeline.Another innovation associated with the pipline is the zig-zag configuration aboveground. Since pipe shifts around far more easily aboveground than when buried, the zig-zag path of the pipeline allows the pipe to move from side to side and lengthwise. This movement may be caused by earthquakes or by thermal expansion and contraction. The VSMs also include "shoes" to allow for horizontal or lateral movement, and crushable blocks to absorb shocks from earthquakes, avalanches, or vehicles.