page_title: Construction of the Trans-Alaska Pipeline System
section_title: Survey and design
hierarchical_section_title: Construction of the Trans-Alaska Pipeline System / Survey and design
caption_attribution_description: English: A vertical support member of the Trans-Alaska Pipeline is seen topped by two radiators connected to heat pipes.
context_page_description: The construction of the Trans-Alaska Pipeline System included over 800 miles of oil pipeline, 12 pump stations, and a new tanker port. Built largely on permafrost during 1975–77 between Prudhoe Bay and Valdez, Alaska, the $8 billion effort required tens of thousands of people, often working in extreme temperatures and conditions, the invention of specialized construction techniques, and the construction of a new road, the Dalton Highway.
  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.
context_section_description: Intensive geological sampling and survey work of the pipeline route started in spring 1970. Aerial photograph 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 gravel 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 
caption: Radiators atop heat pipes keep permafrost below the pipeline frozen.
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