Maintenance
The pipeline is surveyed several times per day, mostly by air. Foot and road patrols also take place to check for problems such as leaks or pipe settling or shifting. The pipeline can be surveyed in just two hours, but most surveys take longer to ensure thoroughness. These external inspections are only part of standard maintenance, however. The majority of pipeline maintenance is done by pipeline pigs—mechanical devices sent through the pipeline to perform a variety of functions.
The most common pig is the scraper pig, which removes wax that precipitates out of the oil and collects on the walls of the pipeline. The colder the oil, the more wax buildup. This buildup can cause a variety of problems, so regular "piggings" are needed to keep the pipe clear. A second type of pig travels through the pipe and looks for corrosion. Corrosion-detecting pigs use either magnetic or ultrasonic sensors. Magnetic sensors detect corrosion by analyzing variations in the magnetic field of the pipeline's metal. Ultrasonic testing pigs detect corrosion by examining vibrations in the walls of the pipeline. Other types of pigs look for irregularities in the shape of the pipeline, such as if it is bending or buckling. "Smart" pigs, which contain a variety of sensors, can perform multiple tasks. Typically, these pigs are inserted at Prudhoe Bay and travel the length of the pipeline. In July 2009, a pig launcher was installed at Pump Station 8, near the midpoint of the pipeline.
A third type of common maintenance is the installation and replacement of sacrificial anodes along the subterranean portions of pipeline. These anodes reduce the corrosion caused by electrochemical action that affect these interred sections of pipeline. Excavation and replacement of the anodes is required as they corrode.
Read more about this topic: Trans-Alaska Pipeline System
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