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40 Years at Prudhoe Bay: Pipeline tops for moving oil to market Companies organize unprecedented engineering feat to overcome technical challenges of transporting Prudhoe Bay crude to tidewater Petroleum News
Even while Put River No. 1 was being drilled, the three companies most concerned with Prudhoe Bay at that time — British Petroleum, Atlantic Richfield and Humble (predecessor to ExxonMobil) — initiated a full-scale study of all possible alternative routes for moving the oil off the North Slope.
In October 1968, BP, ARCO and Humble formed a joint venture to organize, design and build a pipeline to transport Prudhoe Bay oil to market. The new enterprise was called Trans-Alaska Pipeline System, or TAPS.
ARCO and BP each initially held a 37.5 percent interest in the line and Humble held a 25 percent share. Those ownership interests changed over the next 40 years. Today, BP owns 50.3 percent, while ConocoPhillips holds 28.1 percent and ExxonMobil retains a 20.3 percent stake.
In 1968, the big three soon-to-become producers extended an invitation to other companies that might wish to transport oil from the North Slope in the future. This led to four other companies — Mobil Alaska Pipeline Co., Amerada Hess Pipeline Co., Phillips Alaska Pipeline Corp. and Unocal Pipeline Co. — joining TAPS.
Trans-Alaska pipeline chosen to move oil In February 1969 TAPS announced plans to build a trans-Alaska crude oil pipeline south from Prudhoe Bay to the nearest ice-free port. TAPS aimed to build a 789-mile (revised later to 798 miles), 48-inch diameter pipeline from Prudhoe to the port of Valdez on Prince William Sound on Alaska’s southern coast. The initial estimated cost of the project was $900 million - the most expensive ever proposed by private industry at the time. Inflation and environmental considerations eventually drove the final cost to more than 10 times that amount.
Route feasibility studies indicated that an obscure pass through the Brooks Range was the best route for the pipeline. The pass had never been named. “Early on,” Mull said, “the companies referred to it as Dietrich Pass,” but later it was officially named Atigun Pass.
“All of us working on the Slope at the time just assumed the line would go through Anaktuvuk Pass,” he said.
Though Atigun was higher than Anaktuvuk Pass, an alignment of the route linking these principal points — Atigun Pass, Rampart Canyon and Valdez — was selected. Criteria included keeping the pipeline profile within the limits of past experience in relation to mountain crossings. This involved intensive studies to ensure the pipeline was not pressured past design specifications; minimizing the length of the line; ensuring that the line could be buried for the greatest possible distance; minimizing the distance it would have to run in high ice-content permafrost areas; bypassing identifiable geologic hazards; avoiding terrain and soil conditions which could present undue construction difficulties, minimizing alignments requiring large amounts of grading, such as side-hill construction; bypassing population centers; and wherever possible, avoiding sites of antiquities and important fish spawning or wildlife areas.
Soil conditions along the route, which could influence the pipeline’s alignment or mode of construction, were studied in considerable detail. More than 3,000 bore holes were drilled from Valdez to Prudhoe Bay, from which more than 30,000 core samples were taken.
Pre-construction costs of the Alyeska pipeline totaled more than $100 million. The bulk of that was in soil investigations, in determining methods of pipe support, in testing the pipe itself, which came from three companies in Japan, and in compiling environmental baseline data.
The size and scale of the project was daunting. The pipeline would cross the Denali fault line on the north side of the Alaska Range, an area known to be seismically active, and 600 streams and rivers.
Three mountain ranges also would be crossed by the pipeline – the Brooks, Alaska and Chugach mountains. The point of highest elevation is 4,739 feet at Atigun Pass in the Brooks Range. The steepest grade is 55 degrees at Thompson Pass in the Chugach Range.
Unprecedented technical challenge Designing the pipeline was an unprecedented engineering challenge. Thousands of bore-hole core samples were analyzed. Seismic experts at the U.S. Geological Survey in Menlo Park, Calif., reviewed reams of data to assess earthquake risk. Extensive stress analyses on the pipe were conducted
Several factors made the design of the line unprecedented in terms of complexity.
The 48-inch pipeline system had to be able to achieve a throughput of 1.5 million barrels per day . It had to be built to address three different soil conditions – normal soil where the pipeline could be buried in a conventional manner, discontinuous permafrost where the pipeline could be buried if adequately insulated and continuous permafrost where the pipeline would have to rest on an elevated pipe rack, or vertical support members, whose pilings were constantly cooled to prevent heating and thawing of the permafrost.
The 48-inch diameter mainline pipe was delivered to Alaska in the early 1970s from three companies in Japan – Sumitomo Metal Industries, Yawata Iron and Steel, and Nippon Kokan. The 69,000 lengths of pipe were stockpiled at large sites in Valdez, Fairbanks and Prudhoe Bay. Total pipe cost about $120 million.
The pipe had to be strong with wall thicknesses of 0.462 and 0.562 inches and specified minimum yield strengths of 60,000-70,000 pounds per square inch. These specifications would meet or exceed the requirements for safety and special low temperature considerations as well as all U.S. government and American Petroleum Institute standards.
The pipeline system had to be built to withstand the combined stress of internal pressure of thermal, bending and seismic forces.
At river crossings and in certain flood plains, it required anti-corrosive coating and an outside layer of concrete to anchor it to stream bottoms. All buried sections required anti-corrosion costing and cathodic protection with sacrificial zinc anodes to prevent chemical and electrolytic corrosion of the pipeline.
Above-ground sections (about half the line) required thermal insulation to slow the drop in oil temperature in the event of a pipeline shutdown.
Geotechnical, geological, civil and Arctic engineering, stress analysis, thermal engineering, agronomics, hydraulics, mechanical and welding engineering were all required. This wide-ranging array of engineering disciplines produced the most detailed design of any pipeline ever constructed. Also significant was that it was constructed within a short period of time — a mere three years.
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