Trans-Alaska Pipeline System
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The Trans-Alaska Pipeline System (TAPS), usually called the Alyeska Pipeline in Alaska or the Alaska Pipeline elsewhere, is a major U.S. oil pipeline connecting oil fields in northern Alaska to a sea port 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 towns, including Wiseman, Bettles, Livengood, Fox, Fairbanks, and Glennallen [see map].
Construction of the pipeline presented significant challenges due to the remoteness of the terrain and the harshness of the environment it had to pass through. Geological activity has damaged the pipeline on several occasions. Since its completion in 1977, the pipeline has transported over 15 billion barrels (2.4 km3) of oil.
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[edit] Construction
Oil was discovered at Prudhoe Bay, Alaska in 1968, after explorers had been searching all over Northern Alaska since the 1950s. A pipeline was considered the only viable system for transporting the oil to the nearest ice-free port, almost 800 miles (1,300 km) away at Valdez.
The oil companies with exploration rights grouped together as the Alyeska consortium to create a company to design, build, and then operate the pipeline. US President Richard Nixon signed the Trans-Alaska Pipeline Authorization Act into law on November 16, 1973, which authorized the construction of the pipeline.
The single 48 inch (1.22 m) diameter pipeline was built between March 27, 1974 to May 31, 1977 at a cost of around US$8 billion. The pipe was constructed in six sections by five different contractors employing 21,000 people at the peak of work; 31 were killed in accidents during construction.
The 799 mile (1,286 km) route presented special challenges. As well as the harsh environment, the need to cross three mountain ranges and many rivers and streams, the permafrost of Alaska meant that almost half of the pipeline's length had to be elevated rather than buried as normal to prevent the ground melting and shifting. There were five years of surveying and geological sampling before construction began. During construction archaeological teams were repeatedly called in to investigate previously unknown sites which were disturbed by excavation.
[edit] Technical details
Along the pipeline there are eleven pump stations, each with four pumps. Each electric pump is powered by diesel or natural gas generators. Twelve pump stations were planned but Pump Station 11 was never built, though the southward numbering system for the pump stations retains a place for this nonexistent station. Usually only around seven stations are active at one time, and future plans to replace the existing pumps with newer high-efficiency pumps may reduce the number of active stations even further.
The pipeline was built above ground in areas where thaw-sensitive permafrost exists. However, where the line must be buried, such as highway crossings or avalanche-prone areas, the pipe is encased in an insulated, refrigerated ditch. Nearby refrigeration plants pump cold brine through 6 inch (15 cm) pipes which absorb heat and keep the soil cooled. Other areas of burial are either conventional covered ditches or unrefrigerated but insulated ditches, depending on the sensitivity of the surrounding soil.
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 from occurring, 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 VTM. Running through the VSM, the heat pipe transports heat from the VTM base to the heat exchanger. Since ammonia, the working fluid in heat pipes, has a freezing point lower than the permafrost, the heat pipe works throughout the year, even during the coldest winter nights. This relatively simple convection cooling system is thought by TAPS engineers and maintainers to be the greatest technological 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 it does when buried, the zig-zag path of the pipeline allows the pipe to move somewhat from side to side and lengthwise. This movement may be caused by earthquakes or by temperature-related expansion and contraction. The VSMs also include special "shoes" to allow for this horizontal or lateral movement, and crushable blocks to absorb sudden shocks from earthquakes, avalanches, or vehicles.
Oil began flowing on June 20, 1977. Since then over 15 billion barrels (2.3 km³) have been pumped, peaking at 2.1 million barrels (330,000 m³) per day in 1988. Around 16,700 tankers had been loaded at the Marine Terminal at Valdez by 2001. The terminal has berths for four tankers and cost almost US$1.4 billion to build. The first tanker to leave the terminal was the ARCO Juneau on August 1, 1977.
[edit] See also
[edit] References
[edit] External links
- Alyeska Pipeline website
- Pipeline facts
- The Alaska Pipeline - Related American Experience episode
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