(Editor’s Note: This article is the fourth in an occasional series on iconic United States construction projects.)
The Trans-Alaska Pipeline System is not only one of the most remarkable and difficult construction feats in U.S. history, it also is beautiful as it climbs over mountains, hangs over deep blue rivers, and zigzags over arctic tundra.
Chances are good that many haven’t thought of the Prudhoe Bay oilfield, or the pipeline, very often over the past few years. Now, with two feeder (transit) lines on the east side of the field closed because of corrosion cutting pipeline throughput from the 750,000-barrels-per-day average for August to probably between 550,000 to 600,000 barrels per day, the pipeline is probably on people’s minds a lot, especially at the gas pump.
It’s a good time to reflect on how the nation met — and conquered — a stupendous challenge when it constructed, in just two years (between March 27, 1975, and May 31, 1977) the 800-mi.-long (1,287 km), 4-ft. diameter (1.2 m) steel pipeline from Prudhoe Bay on Alaska’s North Slope, through Fairbanks, to Valdez, the state’s northernmost ice-free port, on Prince William Sound.
Geologists had been looking for oil on Alaska’s North Slope as early as 1959. When Atlantic Richfield Co. (ARCO) and Humble Oil and Refining Co. (now EXXON Co., U.S.A.) verified in 1968 that there was a large oil field there, oil companies leapt at the opportunity of drilling the new field.
The two-year construction project cost $8 billion and was, at the time, the largest privately funded construction project in U.S. history. Building the pipeline used just about every type of earthmoving equipment, from backhoe loaders to tractors, excavators and trucks, for everything from clearing the right of way to digging trenches, cutting through bedrock and erecting bridges.
The new find turned out to be a real bonanza. It’s the 18th largest oil field yet discovered, and the largest yet found in North America.
“At first, they thought the new oil field held about nine million barrels of oil, but it proved to hold much more and be the nation’s largest oil field,” said Curtis Thomas, corporate communications manager in Fairbanks, AK, of Alyeska Pipeline Service Co., which is responsible for the design, construction, operation and maintenance of the pipeline for the owner companies. The owners are BP Pipelines (Alaska) Inc., Exxon Pipeline Co., Mobil Alaska Pipeline Co., Amerada Hess Pipeline Corp., Phillips Alaska Pipeline Corp., and Unocal Pipeline Co.
(The name Alyeska comes from a middle-ranking female wolf of the Gallatin pack.)
Pipeline Handles Big Output
The Prudhoe Bay oil field, owned by BP, ExxonMobil and Conoco Phillips, with the 13 North Slope oil fields operated by BP Exploration (Alaska) Inc., is now estimated to hold at least 25 billion barrels of oil. Since one barrel equals approximately 42 gallons, that’s approximately 1,050 billion gal. The field has produced more than 1,500,000 barrels a day in some past years. Output at the time of the shutdown was approximately 850,000 barrels a day, or approximately 17 percent of domestic oil production.
An estimated 15 billion barrels of crude have been pumped through the pipeline from the North Slope since 1977. The pipeline is now a central part of an immense infrastructure covering 5,000 acres (2,023 ha) of the North Slope. Prudhoe Bay now includes 3,898 exploratory wells, 170 drilling pads, 500 mi. (804.7 km) of road, 1,100 total mi. (1,770.3 km) of pipeline (including feeders), five docks, and 25 production, processing, sea water treatment and power plants.
Six-Year Planning Effort
After the big news in 1968, oil firms, including Humble, Atlantic, BP Pipeline, Amerada Hess, Home Pipe Line, Mobil Pipe Line, Phillips Petroleum and Union Oil Co. of California, formed a joint venture for a planning study and for engineering, design and construction of the Trans-Alaska Pipeline System (TAPS).
The pre-construction planning was itself a huge project, taking six years. A $2.2-million archaeological survey by the University of Alaska and Alaska Methodist University excavated approximately 330 sites. Surveying the soil from Prudhoe to Valdez involved 3,500 bore holes and approximately 15,000 soil samples. A total of 515 federal and 832 state permits were required for right of way and other purposes.
Approximately 2,000 contractors and subcontractors were selected. Five contractors were each given responsibility for different sections of the pipeline. These were Morrison-Knudson-Rivers, Perini Arctic Associates, H. C. Price, Associated Green, and Arctic Constructors.
A total of 70,000 contractor personnel worked on the pipeline over the life of the project, from 1969 to 1977. At its peak, in October 1975, the project involved 28,072 people, including Alyeska employees and contractors. There were 31 fatalities directly related to the construction, including Alyeska, contractors and subcontractors.
Crossing the Mountains
Planners chose a direct route south. This meant first going over the Atigun Pass, which at 4,728 ft. was the highest point on the pipeline, and later crossing the Isabel Pass (3,566 ft.) and Thompson Pass (2,810 ft.). The steel pipe also would cross three major mountain ranges (the Brooks, the Chugach and the Alaska), and 800 rivers or streams.
“Up and over is a lot shorter than around and about,” Thomas said. “The construction was remarkable because we crossed some of the most hazardous, delicate and environmentally sensitive terrain in the world.”
The oil is pumped over the mountains hydraulically. Four different pump stations, for instance, successively raise the pressure of the oil to pump it over the Atigun.
Fourteen temporary airfields were built. Seven of these were 2,500 to 3,000 ft. long and seven were 5,000 ft. long. Two of the latter continue to be used for the pipeline.
Between 1974 and 1977, contractors built 29 construction camps. The largest of these, at the Valdez Marine Terminal, held 3,480 beds. The largest at the pipeline itself, at Isabel Pass, held 1,652 beds.
More than 225 access roads were built, linking state roads with the pipeline, pumping stations and airfields.
Thirteen bridges also were built for the pipeline system, including two suspension types in which the pipe is suspended from large steel cables draped over towers and anchored to massive foundations on opposite banks. The Tanana River suspension crossing is 1,300 ft. (396 m) long.
Construction Begins
The first 48-in.-diameter (122 cm), .5-in.- thick (1.3 cm) pipe section actually arrived at Valdez from Japan (the pipe supplier) in September, 1969.
As the project picked up steam, the Trans-Alaska Pipeline Act became law in 1973, a federal right of way grant was issued in January 1974, and a $150-million, 360-mi. (579.4 km) road, now known as the Dalton Highway, was built from Prudhoe Bay to the Yukon River between May and September 1974, to supply the North Slope facilities.
The first pipe was laid at the Tonsina River on March 27, 1975, the official start of the actual construction. The pipeline bridge over the Yukon River, the only span across that river in Alaska, was completed on Oct. 11. By Oct. 26, the pipeline project was 50 percent complete.
The first crude oil flowed through the pipeline from Pump Station 1 (PS 1) on June 20, 1977. Oil, natural gas, water, and sediments, pumped from wells, were sent through pipelines to processing plants to be separated. The oil, gathered in tanks at the station, was then pumped through the pipeline. At Valdez, the oil was loaded on the tanker ARCO Juneau on Aug. 1. (Eighteen storage tanks at Valdez can hold 9.1 million barrels of oil. More than 20,000 tankers have been loaded at Valdez, which is the operations control center for TAPS.)
Three million tons of materials, including pipes, were shipped to Alaska for the pipeline system. The project used a total of 73 million cu. yds. (55.8 million cu m) of gravel. A total of 42,000 double joint welds and 66,000 field girthweld were used on the pipe.
Conquering the Obstacles
Considering the obstacles, completing the job in just two years was an amazing feat.
Since the oil is heated, approximately 420 mi. of the pipeline is elevated on vertical supports above the ground.
“We elevated the pipe in these areas to protect the permafrost,” Thomas said.
Permafrost is any rock or soil material that has remained below 32F continuously for two or more years.
The hot pipeline, if on the ground, could thaw unstable, poorly drained, fine-grained soils, which usually contain large amounts of ice, especially when they are “warm permafrost” just below 32F. This melting could cause the pipeline structure to sink into the ground.
Engineers also had to contend with “frost-heaving” when ice forms and pushes the ground surface upward, with “frost-jacking” of the pipeline structure.
The elevated system includes specially designed vertical supports, which are placed in drilled holes or driven from 15 ft. to 70 ft. (4.6 to 21,3 m) into the ground. TAPS includes 78,000 of these supports, usually 18 in. (45.7 cm) in diameter and 60 ft. (18.3 m) apart.
If the pipeline had to be buried in these areas to go under highways, provide animal crossings, or to avoid possible avalanches, the line was insulated to protect the permafrost from the pipeline’s heat.
In warm permafrost and other areas where heat might cause thawing, the supports contain two 2-in. (5 cm) “heat pipes” containing anhydrous ammonia. The ammonia vaporizes below ground, but rises and condenses above ground, removing ground heat whenever the ground temperature exceeds the temperature of the air.
Above-ground sections of the pipeline are built in a zigzag configuration. This allows for expansion or contraction of the pipeline because of temperature changes. When the first warm oil was put in the pipeline during start-up in 1977, the above-ground pipe lengthened almost 4 ft. (1.2 m) per mile. A straight pipeline would not have the flexibility to absorb that much growth. When the pipeline crosses the Denali Fault, it is designed to slide up to 20 ft. (6.1 m) horizontally and 5 ft. (1.5 m) vertically. The zigzag design also allows for pipeline movement caused by an earthquake.
TAPS includes 554 elevated (often arched) animal crossings, with a minimum height of 10 ft. (3 m), allowing caribou and other wildlife to pass under it on their trails.
Below-Ground Sections
Approximately 376 mi. (605 km) of the pipeline, where there is solid bedrock not threatened by permafrost, is conventional below-ground construction. The pipeline is buried in a ditch that is 8 to 16 ft. (2.4 to 4.9 m) deep in most locations, but up to 49 ft. (14.9 m) deep in one place.
Below-ground pipe is underlain with a layer of fine bedding material and covered with prepared gravel padding and soil fill.
In one 4-mi. area, the line is insulated and buried in a refrigerated ditch. Refrigeration plants circulate chilled brine through loops of 6-in. (15.2 cm) diameter pipe to maintain the soil in a stable frozen condition.
Protecting Against Corrosion
The pipeline includes special corrosion protection (especially relevant because corrosion has been called the cause of the current feeder line problem).
Zinc ribbons, which serve as “sacrificial anodes” to inhibit corrosion of the pipe, are buried alongside the pipeline. An 8.5-mi. (13.7 km) Atigun Pass replacement section uses four magnesium ribbon anodes instead of zinc.
The pipeline and zinc anodes pick up electrical (telluric) currents in the earth’s surface, which are caused by the same phenomenon that generates the Northern Lights. The anodes act like grounding rods to safely return these currents back to the earth, reducing the risk of corrosion damage.
Alyeska also uses an inspection device, called a “smart pig,” to travel through the inside of the pipeline and measure wall thickness. Sources said the feeder lines where corrosion was found had not been inspected with this device since 1992 because the pipes were too clogged with sludge.
There have been numerous leaks throughout the pipeline’s history. BP discovered a 270,000-gal. (1.02 million L) spill, also attributed to corrosion in a transit line, on the oil field’s west side last March. This was the worst spill since production began on the North Slope
Sabotage
Besides corrosion, the pipeline also has been subject to sabotage. Alyeska’s chronological list of events said there was a large oil spill due to sabotage on Feb. 15, 1978. One Web site said approximately 670,000 gal. (2.536 million L) of oil spilled in 1978 after a hole was blasted with explosives near Fairbanks. It also said the pipeline was “shot by a drunk” in October 2001. A surveillance crew detected a bullet hole in the pipe from a rifle, causing production to be reduced by 50 percent. A suspect was charged with shooting the pipeline with a rifle, criminal mischief, driving while drunk and assault.
New Advances
Alyeska is in the middle of reconfiguring the pipeline.
“We’re switching the way we pump the oil in certain locations, switching to electricity at certain pumping stations,” Thomas said. “There’s still drilling going on for new discoveries.”
Thomas said Alyeska has maintained a comprehensive program of monitoring, inspections and maintenance to fight against corrosion of the pipeline, and that the company began a high-tech inspection of the line after the March spill.
Possible Effects
Observers said the loss of production could cause gas prices to rise on the West Coast, though other worldwide suppliers, and use of the nation’s strategic oil reserve, are filling some of the shortfall.
Alaska receives 89 percent of its income from oil revenue. It has no state sales tax and no personal income tax.
Gov. Frank Murkowski imposed a hiring freeze in the state because of the lost revenue. He said he would ask the state attorney general to investigate whether the state could hold BP fully accountable for the state’s losses.
(More information is available on www.alyeska-pipe.com or www.trans-alaska/pipeline.com) CEG
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