Trans-Alaska Pipeline at 60 years of age

The recent acquisition of the NDT contracting company where I work, by a large corporation listed on the New York Stock Exchange, made me more aware of the ongoing NDT requirements associated with the maintenance and integrity of the Trans-Alaska Pipeline. My online research detected a web page article, which lists no author…

The Trans-Alaska Pipeline is 800 miles long and one of the most historic welding and construction projects in history. For three years, tens of thousands of welders braved the harsh climate and terrain of Alaska’s wilderness to weld together the 48-inch diameter of the pipeline. Since then, more than 17 billion barrels of oil have flowed from the Prudhoe Bay Oil Field in Northern Alaska down to Valdez Bay.

Construction of the massive pipeline began in 1975, at a time when construction was in a slump throughout the United States. The men who welded the pipeline came all the way from the Pipeliners Local 798 Union out of Tulsa, Oklahoma. This group specialised in providing welders for large-scale pipeline projects and the Trans-Alaska Pipeline was probably the largest up to that point.

The hiring process was very intense because of the immensity and importance of the pipeline. Welders were first put through a certification process that involved several test welds. If the welder failed any of the test welds, they were not hired and were not allowed to be tested again for several weeks.

The first step in the pipeline construction involved clearing the 800-mile path laid out by surveyors. Workers slowly trudged their way through forest, brush and obstacles using chainsaws and bulldozers. Once the path was cleared, holes were drilled and filled with gravel and water. These served as the foundations for the vertical support members that held up the pipeline using semicircular supports. These support members were carried by crane in 40- or 80-foot segments, lowered into the holes and then welded together. Welds were radiographed for quality acceptance.

With several vertical support members already in place, workers officially laid the first portion of the Trans-Alaska Pipeline on 27 March 1975. 40-foot segments were placed atop the supports, welded together and coated in concrete. So began the two-year long process of welding construction on the pipeline.

The welded joints were made using submerged arc welding and a wire that contained 3% nickel. About 80,000 lb of that wire was used throughout the entirety of the pipeline project.

Midway through the construction process, the US Department of the Interior and a pipeline-coordinating group representing the state of Alaska instituted more stringent requirements for weld toughness. Instead of the conventional electrode that was originally used for the majority of field welds, new requirements necessitated a higher-quality electrode using an E8010-G filler metal. This electrode had to be flown into Alaska from Germany. It was an electrode that most welders on the project had never used before.

Throughout the project, welders worked inside protective aluminium enclosures that shielded them from the wind and other harsh weather conditions. This also gave them the lighting they needed to work through the night. Welds were inspected using radiography. The NDT inspectors travelled alongside the welding crews in mobile film-processing vehicles.

The final pipeline weld was completed on 31 May 1977. The pump station and terminal construction still needed to be completed, but the pipeline could be put into operation before this happened. Three months later, the tanker Arco Juneau sailed out of Valdez with the first load of oil that had travelled through the Trans-Alaska Pipeline.

So impressive was the project and the welding that in 2002 the American Welding Society declared the Trans-Alaska Pipeline an outstanding development in welded fabrication. The Alyeska Pipeline Service Company was presented with an award and congratulated on the immense project they had helped create.

By law, Alyeska is required to remove the pipeline once oil extraction in the Prudhoe Bay Oil Field is complete. Improvements in reducing flow rates seem to suggest the oil could be flowing through the pipeline until at least 2075, meaning this welding wonder could last 100 years.

Numerous current NDT and asset management projects have been applied to the continuing viability of the pipeline. Guided wave ultrasonic technology has been significantly used for testing, with particular importance at road crossings and buried sites, where permanent sensors have been attached for ongoing evaluations.

Traditional NDT methods, such as phased array ultrasonics, UT thickness measurement, eddy current testing, 3D laser scanning, electromagnetic acoustic evaluation and computed radiography, are currently in use.

The entire 800-mile length has been provided with cathodic protection, protective coatings have been applied and the quality assurance and code compliance programmes are assiduously applied under the eagle eyes of state and federal oversight inspectors.

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