Headquartered in Anchorage, Alaska, Alyeska Pipeline Service Company was formed to design, build, operate and maintain the Trans Alaska Pipeline System (TAPS). Construction began in 1975 and was completed in 1977. Costing $US8 billion, the pipeline was the largest privately funded construction project at the time.

TAPS transports crude oil from the oil fields of Alaska’s North Slope across 1,200 km of tundra, rugged mountains, and rivers to Valdez — the northernmost ice-free port in North America.

Design engineers faced many challenges, including the stability of permafrost and the three fault lines along the pipeline route.

Alyeska says TAPS was originally designed with 12 pump stations. However, only 11 were determined to be needed and were eventually constructed. Four pump stations (PS 1, 3, 4, 9) currently pump oil through the line.

Breaking the ice

Approximately 600 km of the pipeline is buried, while about 675 km is above ground to avoid burying the pipe in permafrost, which is ground that is continuously frozen for two years or more. Alyeska explains that because the crude oil is warm, heat from a buried pipe could warm the permafrost, making the soil in some areas unstable.

Where the pipeline is buried in permafrost it is either insulated or refrigerated to keep the permafrost from thawing. Refrigeration plants at each of these points circulate chilled brine through loops of 6 inch diameter pipe to maintain the soil in a stable frozen condition.

Above-ground portions of the pipeline sit on vertical support members (VSMs). The majority of the pipeline’s 78,000 VSMs are equipped with heat transfer pipes and radiators that keep the permafrost beneath the supports frozen. In areas where heat might cause undesirable thawing, the supports contain two pipes, 2 inches in diameter, containing anhydrous ammonia, which vaporises below ground, rises and condenses above ground, removing ground heat whenever the ground temperature exceeds the temperature of the air. Heat is transferred through the walls of the heat pipes to aluminium radiators atop the pipes.

In addition, the VSMs allow the pipeline to move a certain amount, both vertically and horizontally, in case of earthquakes and to compensate for expansion and contraction.

The above-ground sections have also been constructed in a zigzag configuration, which allows for expansion or contraction of the pipe due to temperature changes. This design also allows for any pipeline movement that might occur because of earthquakes in the area.

In areas of thaw-unstable soils where the pipeline had to be buried for highway, animal crossings, or avoidance of rockslides and avalanches, the line was insulated, to protect the permafrost from the heat of the pipeline, and buried.

Considering nature

Alyeska’s engineers designed the 48 inch diameter pipeline to endure and protect Alaska’s unique but harsh environment, as the pipeline traverses three mountain ranges, three major earthquake faults and more than 500 rivers and streams.

The pipeline design also took into account wildlife, allowing caribou, moose, and other animals to easily cross the pipeline corridor at some 550 locations.

Alyeska says “One of the three fault lines, the Denali Fault, registered a 7.9 earthquake in 2002. The pipeline withstood the earthquake with only minor damage, much the way the original design team intended.”

The scenery along the pipeline route is magnificent, rivalled only by the picturesque route the tankers transit through Prince William Sound. Alyeska says the pipeline is arguably one of the most photographed in the industry. It has also been the subject of many documentaries over the course of 30 years, most recently featured on the PBS (US-based televsion station) series American Experience.

Operational milestones

Over the pipeline’s lifetime, more than 15 Bbbl of oil have been transported via the pipeline, and over 19,000 tankers have taken the oil to market. At the height of North Slope production, the pipeline was transporting more than 2 MMbbl/d of oil. Current throughput is approximately 740,000 bbl/d.

Currently, Alyeska is dealing with operational issues associated with operating at lower throughput ranges. The company says its engineers are studying these issues and are working on presenting technical solutions to help mitigate these challenges.

Alyeska operates TAPS on behalf of five owner companies: BP Pipelines (Alaska), ConocoPhillips Transportation Alaska, ExxonMobil Pipeline Company, Unocal Pipeline Company, and Koch Alaska Pipeline Company.

In addition to its Anchorage headquarters, the company also maintains operations in Fairbanks and Valdez and at various pump stations along the pipeline route.