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Construction of the Trans-Alaska Pipeline System

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  • 9 chapters

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Through Construction, Pipeline and Thermal expansion

The first section of pipe was laid in 1975 after more than five years of legal and political arguments. Allegations of faulty welds drew intense scrutiny from local and national observers. A culture grew around the unique working conditions involved in constructing the pipeline, and each union that worked on the project had a different function and stereotype. Thirty-two Alyeska Pipeline Service Company employees and contract workers were killed during the project. The main construction effort lasted until 1977; the first barrel of oil was delivered on July 28 of that year. Several more pump stations, added as oil flow increased, were completed through 1980.

Survey and design

Intensive geological sampling and survey work of the pipeline route started in spring 1970. Aerial photographs were taken, examined, and a preliminary route was detailed. Small survey parties physically visited the route and hammered stakes into the ground. The work was difficult; animal dangers forced the crews to be armed, and they also had to cope with the remote area and limited infrastructure. In places, the foliage was so dense that trees had to be cut down and progress was limited to 20,000 feet (6.1 km) per day. The surveyed route passed through several mountain passes: Atigun Pass, Isabel Pass, Thompson Pass, and Keystone Canyon. In the latter location, surveyors had to rappel down cliffs in order to perform their work.

Surveyors and planners also had to deal with the Denali Fault, a major cause of earthquakes, and with large amounts of permafrost. In 1969, the unincorporated Trans-Alaska Pipeline System group drilled a series of core samples north of the Brooks Range that demonstrated how ubiquitous the permafrost was along the route. This forced the design of an elevated pipeline, which was tested in a 1,000 feet (300 m) loop built near Barrow. This elevation required the pipeline to be insulated, since extreme cold temperatures caused the metal to become brittle, even when hot oil was being pumped through the pipeline.

After ecological objections forced subterranean pipeline crossings (in order to allow caribou to cross), engineers developed a system by which the ground near the pipeline would be refrigerated by chilled brine. These refrigerated sections also would be placed in Styrofoam-lined trenches and covered with gravel for their insulation value. Altogether, 3.5 miles (5.6 km) of the pipeline was designed to be built underground in this way. In other places, a lack of permafrost meant it could simply be placed underground without a special refrigeration plant. Large amounts of gravel were needed for all sections of the pipeline as insulation to keep the heat of above-ground structures from melting the permafrost. Gravel also was needed to build the construction and maintenance road, and surveyors located 470 sites across Alaska where the needed 65,000,000 cubic yards (50,000,000 m3) of rock could be located.

The Pipeline Authorization Act required the pipeline to be able to withstand the maximum earthquake ever recorded in the area it was built. When crossing the Denali Fault, Teflon-coated sliders were designed to allow the pipeline to move side-to-side in an earthquake. To protect against forward-and-backward shocks and to allow for thermal expansion, the pipeline wasn't designed as a straight line. Instead, it was intended to be laid in an S-shape, and the bends would allow for expansion and movement without breaking.

Because most of the pipeline was built above permafrost, each of the pipes holding up the raised sections of pipeline contained a sealed tube of ammonia. As the permafrost below the pipeline warms, the ammonia absorbs the heat and rises to a radiator on top of each stanchion. The ammonia is cooled by the outside air, condenses, and falls back to the bottom of the tube, where the process repeats.

The surveyed route crossed hundreds of streams and rivers. To cross these with the pipeline, engineers designed concrete "jackets" to surround the pipe and weight it down so it would sink to the bottom of the stream or river. Because oil is lighter than water, the pipeline would float without the concrete jackets. Dredging rivers and burying the pipeline in the streambed was not allowed due to environmental concerns. In several places—either out of fear of disturbing the river or because of the river's characteristics—pipeline bridges were constructed. The most notable of these are over the Yukon River and the Tanana River. To protect against corrosion in these wet environments, the pipeline was designed with cathodic protection.

In terms of spill prevention, the pipeline was designed with one-way valves (so oil moving ahead could not leak out of a hole behind a certain point), computer-aided leak detection, and other features. The pipeline was designed to be pressurized, so any leak would be instantly detected by a loss of pressure at one of the pump stations, which could sound an alarm and halt the flow of oil quickly.

The original pipeline proposal called for an initial capacity of 0.6 million barrels per day (95,000 m3/d), then an increase to 1.2 million barrels per day (190,000 m3/d) after two years, and then a further increase to 2 million barrels per day (320,000 m3/d) at an indeterminate time thereafter. The events of the 1973 oil crisis caused a review of these plans, and the initial capacity was revised upwards to 1.2 million barrels per day (190,000 m3/d). This in turn required that eight pumping stations (instead of the originally-planned five) be ready at startup, greatly increasing the construction manpower required.

Valdez Marine Terminal

The Valdez Marine Terminal, the southern end of the pipeline, was planned for a site across the Port Valdez fjord from Valdez proper. Initial studies predicted bedrock would be six feet below the surface of the ground, but when excavation began, it was discovered that bedrock was actually sixty feet down, requiring the removal of 15,000,000 cubic yards (11,000,000 m3) of overburden. The terminal itself was designed to be built with four tanker berths and space for a fifth, should it become necessary. Holding tanks were planned that had a capacity equal to that of the pipeline, allowing the whole pipeline to be emptied if required. As required by the Pipeline Authorization Act, a ballast-water filtration system had to be designed as well. This system removes oil from tankers' ballast water so it is not released into Prince William Sound—something fishermen feared when the pipeline was proposed.

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