Editing Trans-Alaska Pipeline System (section)

== Maintenance ==
[[Image:PipelinePIG.jpg|thumb|right|This scraper [[Pig (pipeline)|pig]] was retired from use in the pipeline and is on display near Fairbanks (2007).]]
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 as little as twenty one days, but most surveys take longer to ensure thoroughness.<ref>Carber, Kristine M. [http://www.pobonline.com/CDA/Articles/Cover_Story/da45ca66ea80f010VgnVCM100000f932a8c0____ "Scanning the Alaska Pipeline"], Point of Beginning. December 1, 2006. Accessed July 30, 2009.</ref> These external inspections are only part of standard maintenance, however. The majority of pipeline maintenance is done by [[Pig (pipeline)|pipeline pig]]s—mechanical devices sent through the pipeline to perform a variety of functions.<ref>Facts, pp. 40–41</ref>

The most common pig is the scraper pig,<ref>Facts, p. 40</ref> which removes [[Paraffin wax|wax]] that [[Precipitation (chemistry)|precipitate]]s 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.<ref>Roehner, R.M., Fletcher, J.V., and Hanson, F.V. [http://pubs.acs.org/doi/abs/10.1021/ef010218m "Comparative Compositional Study of Crude Oil Solids from the Trans Alaska Pipeline System Using High-Temperature Gas Chromatography"], ''Energy Fuels''. 2002, 16 (1), pp. 211–217.</ref> 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.<ref>Facts, p. 41</ref> "Smart" pigs, which contain a variety of sensors, can perform multiple tasks.<ref name="newpigs">Bohman, Amanda. [http://www.newsminer.com/news/2009/jul/19/trans-alaska-oil-pipeline-shut-down-maintenance/ "Trans-Alaska oil pipeline shut down for maintenance"]{{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=no }}, ''Fairbanks Daily News-Miner''. July 19, 2009. Accessed July 29, 2009.</ref> 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.<ref name="newpigs"/>

A third type of common maintenance is the installation and replacement of [[sacrificial anode]]s 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.<ref>Alyeska Pipeline Service Co. [http://www.alyeska-pipe.com/Inthenews/LatestNews/2008/August/KeystoneCathodicwork.html "Cathodic protection project wraps up near Valdez"], Alyeska-pipe.com. August 2008. Accessed July 30, 2009. {{webarchive |url=https://web.archive.org/web/20080915200656/http://www.alyeska-pipe.com/Inthenews/LatestNews/2008/August/KeystoneCathodicwork.html |date=September 15, 2008 }}</ref>