Trans-Alaska Pipeline System

Trans-Alaska Pipeline System

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 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) [see map].

Construction of the pipeline through the sparsely-populated region presented significant challenges due to the remoteness of the rugged terrain and the harsh environment along the route. Between the North Slope and Valdez, there were three mountain ranges, active fault lines, miles of unstable, boggy ground underlain with frost, hundreds of streams and rivers, and migration paths of caribou and moose. Geological activity has damaged the pipeline on several occasions.

Since its completion in 1977, the pipeline has transported over 15 billion barrels (2.4 TL) of oil.

Construction

Oil was discovered at Prudhoe Bay, Alaska in 1968, after explorers had been searching all over Northern Alaska since the 1950s. In 1969, Exxon sent a specially fitted oil tanker, the Exxon Manhattan, to test the feasability of transporting oil via ice breaking tankers to market. The Exxon Manhattan, fitted with a massive ice breaking bow, powerful engines, and hardened propellers successfully transited the Northwest Passage from the Atlantic Ocean to the Beaufort Sea. The ship, its cargo holds filled with salt water, suffered some damage to several of its cargo holds. Wind blown ice forced the Manhattan to change its intended route through the McLure Strait to the smaller Prince of Wales Strait. Although the Exxon Manhattan had successfully transited between the Beaufort Sea and the Atlantic Ocean the concept was considered too risky. A pipeline was considered to be 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 16 November 1973, which authorized the construction of the pipeline, Fmr. Sen. Mike Gravel played a crucial role in bringing about the pipeline.

The single 48 inch (1.22 m) diameter pipeline was built between 27 March 1975 to 31 May 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 workers died in construction accidents.

The 800 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 more than 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.

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, 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 temperature-related 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.

Oil began flowing on 20 June 1977. Since then over 15 billion barrels of oil have been pumped, peaking at in 1988 and currently down to (April 2008 average) 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 1 August 1977.

Maintenance

The pipeline is surveyed several times a day, mostly by air. Due to the placement of the surveillance bases, the pipeline can be surveyed in just two hours, but most surveys take longer to ensure thoroughness. Other methods of surveying include regular pipeline inspection gauges ("pigs"), sent through the line. Some pigs are used to remove the buildup of kerosene inside the pipe, while others have electronics which relay radar scans and fluid measurements as they travel.

The pipeline has been damaged several times. It was built with earthquakes in mind and has survived several, including the 7.9 magnitude event of 7 November 2002. It is vulnerable to intentional attack and to forest fires. The highest losses from the pipeline were in February 1978, when a deliberate explosion led to more than 16,000 barrels (2,500 m³) leaking out at Steele Creek, near Fairbanks. From 1977 to 1994 there were 30 to 40 spills a year on average. The worst years in terms of number of incidents were 1991 to 1994, when there were 164 spills, although none were major. Since 1995 the number of spills has been sharply reduced, with total losses from 1997 to 2000 totalling only 6.89 barrels (1.10 m³).

The steel pipe is resistant to gunshots, but on 4 October 2001, a drunken gunman named Daniel Carson Lewis shot a hole into a weld near Livengood, causing a spill of about . Approximately two acres (20,000 m²) of tundra were soiled and were removed in the cleanup. The pipeline was repaired and was restarted on 7 October 2001. Lewis, known as a troublemaker in the community of fewer than 30 people, was apprehended four hours after the shooting. He was convicted on multiple state and federal felony charges, including a $10,000 fine and 10-year federal sentence for being a felon in possession of a firearm.

In August 2006, after an inspection mandated by the United States Department of Transportation after a March spill, BP announced they had discovered corrosion severe enough to require replacement of 16 of of transit pipelines at their Prudhoe Bay oil field. No part of the main Trans-Alaska Pipeline was affected, although Alyeska said that lower crude oil volumes could slow pumping during the BP shutdown.

See also

References

Alaska Agonistes: The Age of Petroleum - How Big Oil Bought Alaska,Joe LaRocca, an anecdotal political history of the modern oil industry in Alaska and some of the social, economic and environmental conflicts it precipitated.

External links

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