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The Trans-Alaska pipeline's engineers drew on all available 1970s technology to design a pipeline that would transport oil from the Arctic Circle to Prince William Sound. What made this pipeline different was that, in the course of its journey, the oil would have to travel up and down three major mountain ranges. At the height of production, in the late 1980s, the Trans-Alaska pipeline was transporting two million barrels of oil a day. Follow the oil as it flows 800 miles from the North Slope to the year-round port of Valdez.
Pumped Over Mountains
At the source in Prudhoe Bay, oil lies several thousand feet below the earth, sealed in and under pressure. When that pressure is released the oil comes flowing out of a well. It is then channeled to the first of eight pump stations. Pumps are required for two reasons. First, natural friction between the oil and the walls of the pipe means that some force is needed to move it along the line. Second, pumps are used to push the oil over mountain ranges. Oil in the pipeline is heavy. Imagine something weighing thousands of pounds and it has to be hoisted up 4,800 feet.
The pump uses centrifugal energy to boost the oil along. When the oil arrives at the pump station it is sucked in to one of three pump units. Each unit has a pump impeller (similar to vanes on a windmill), which twirls the oil very fast. As the oil gains speed, it moves to the outer edges of the impeller blades. Then it is drawn into a second impeller where it gains more momentum by being twirled again. The oil is then forced back into the pipeline, ready to make its mountain ascent. The centrifugal force gives the oil both speed and pressure to flow up steep inclines. At each of the pump stations, a measuring device always tracks how much oil is coming and going. This helps engineers control the flow in the pipeline and will serve as an alert to any leaks.
There are four pump stations between Prudhoe Bay and Atigun Pass in the Brooks Range. At Atigun Pass, the pipeline climbs to its highest point, at an elevation of 4,800 feet. The oil then flows down into the Yukon Basin where it crosses the Yukon River, passes through Fairbanks and across the Tanana Flats. It then climbs again, up towards the Alaska Range. Pump stations 8, 9 and 10 lift the oil through the Isabel Pass. Then the oil flows down into the Copper River Basin. With the help of pump station 12, the oil makes its last ascent up through the infamous Thompson Pass where laborers and welders scaled near-vertical walls to lay the pipe. From the top of the pass, the oil then flows down to the marine terminal in Valdez. Once the oil arrives in Valdez, it is either loaded onto a tanker and transported to a refinery in the lower 48 states, or housed in a holding tank until an empty tanker arrives. In its heyday, traveling at a speed of about seven miles per hour, it would take approximately four or five days for oil to travel the 800 miles from one end of the line to the other.