Editing Trans-Alaska Pipeline System (section)

== Technical details ==
[[File:Trans-Alaska Pipeline System Slider Supports.jpg|thumb|upright|left|The pipeline simply rests on its supports; it is not actually welded or otherwise affixed in place. This is necessary because the air temperature swings by over {{convert|150|F-change}} from winter to summer, causing extreme heat expansion: the length of the pipeline changes by over 5 miles over the course of a year.<ref>Roscow, p. 111</ref> The pipeline was constructed 11 miles "too long" to account for this.<ref>Roscow, p. 115</ref>]]
Oil going into the Trans-Alaska Pipeline comes from one of several oil fields on Alaska's North Slope. The Prudhoe Bay Oil Field, the one most commonly associated with the pipeline, contributes oil,<ref name="Prudhoefacts"/> as do the [[Kuparuk Oil Field|Kuparuk]],<ref>Nelson, Kristen. [http://www.petroleumnews.com/pntruncate/359622793.shtml "Kuparuk Anniversary"], ''[[Petroleum News]]''. January 27, 2007. Vol. 12, No. 3. Accessed July 15, 2009.</ref> [[Alpine Oil Field|Alpine]],<ref>ConocoPhillips. [http://www.conocophillips.com/newsroom/news_releases/2006news/11-27-2006.htm "ConocoPhillips, Anadarko announce start up of second Alpine satellite field"], [[ConocoPhillips]] November 27, 2006. Accessed July 15, 2009. {{webarchive |url=https://web.archive.org/web/20080705120620/http://www.conocophillips.com/newsroom/news_releases/2006news/11-27-2006.htm |date=July 5, 2008 }}</ref> [[Endicott Island|Endicott]], and [[Liberty Oil Field|Liberty]] oil fields, among others.<ref>Delbridge, Rena. [http://www.newsminer.com/news/2008/jul/14/bp-begin-developing-liberty-oil-field/ "BP begins development of Liberty oil field project on North Slope"] {{Webarchive|url=https://web.archive.org/web/20090828063813/http://www.newsminer.com/news/2008/jul/14/bp-begin-developing-liberty-oil-field/ |date=August 28, 2009 }}, Fairbanks Daily News-Miner. July 14, 2008. Accessed July 15, 2009.</ref> Oil emerges from the ground at approximately {{convert|120|F|C}} and cools to {{convert|111|F|C}} by the time it reaches Pump Station 1 through feeder pipelines that stretch across the North Slope.<ref name="Facts18">Facts, p. 18</ref> North Slope crude oil has a [[specific gravity]] of 29.9 [[API gravity|API]] at {{convert|60|F|C}}.<ref>Facts, p. 17</ref> Pipeline flow rate has been steady from 2013 to 2018, hovering just over half a million barrels per day. The minimum flow year was 2015 which averaged {{convert|508446|oilbbl/d|m3/d}},<ref>{{cite web|url=https://www.alyeska-pipe.com/TAPS/FlowAssurance|title=Alyeska Pipeline Flow Assurance|access-date=February 27, 2020|archive-date=May 11, 2020|archive-url=https://web.archive.org/web/20200511081444/https://alyeska-pipe.com/TAPS/FlowAssurance|url-status=dead}}</ref> which is less than its theoretical maximum capacity of {{convert|2.14|Moilbbl/d|m3/d}}<ref name="Facts64">Facts, p. 64</ref> or its actual maximum of {{convert|2.03|Moilbbl/d|m3/d}} in 1988.<ref>Facts, p. 63</ref> From Pump Station 1, the average time taken by the oil to travel the entire length of the pipeline to Valdez has increased from 4.5 days to 18 days from 1988 to 2018.<ref name=FlowAssuranceOverview>{{cite web|url=https://www.alyeska-pipe.com/assets/uploads/pagestructure/TAPS_FlowAssurance_Overview/editor_uploads/Flow%20Assurance%20PP%20Jan%202019.pdf|title=Trans Alaska Pipeline System Flow Assurance Overview}}{{Dead link|date=December 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

The minimum flow through the pipeline is not as clearly defined as its maximum. Operating at lower flows will extend the life of the pipeline as well as increasing profit for its owners.<ref name=AlanBailey>{{cite news |title=A TAPS bottom line |author=Alan Bailey |work=Petroleum News |date=January 15, 2012 |url=http://www.petroleumnews.com/pntruncate/225019711.shtml |access-date=October 27, 2012}}</ref> The 2012 flow of 600,000 bbl/d is significantly less than what the pipeline was designed for. Low flowrates require that the oil move slower through the line, meaning that its temperature drops more than in high-flow situations. A freeze in the line would [[Pigging|block a pig in the line]], which would force a shutdown and repairs.<ref name=AlanBailey/> A 2011 engineering report by Alyeska stated that, to avoid freezing, heaters would need to be installed at several pump stations. This report noted that these improvements could bring flow as low as 350,000 bbl/d, but it did not attempt to determine the absolute minimum. Other studies have suggested that the minimum is 70,000 to 100,000 bbl/d with the current pipeline. Alyeska could also replace the 48" pipeline from Prudhoe Bay to Fairbanks with a 20" pipeline and use rail the rest of the way, which would allow as little as 45,000 bbl/d.<ref name=AlanBailey/>

[[Pumping station]]s maintain the momentum of the oil as it goes through the pipeline.<ref>[http://www.rigzone.com/training/insight.asp?insight_id=344&c_id=19 How Do Pumping Stations Work?]. Rigzone.</ref> Pump Station 1 is the northernmost of 11 pump stations spread across the length of the pipeline. The original design called for 12 pump stations with 4 pumps each, but Pump Station 11 was never built. Nevertheless, the pump stations retained their intended naming system. Eight stations were operating at startup, and this number increased to 11 by 1980 as throughput rose.<ref>Facts, p. 49</ref> As of December 2006, only five stations were operating, with Pump Station 5 held in reserve.<ref>Facts, p. 50</ref> Pump Stations 2 and 7 have a capacity of moving 60,000 gallons/minute (227,125 L/min), while all other stations have a capacity of 20,000 gal/min (75,708 L/min).<ref>Facts, p. 48</ref> The pumps are natural-gas or liquid-fueled turbines.<ref name="Facts64"/>

Because of meanders and thermal and seismic accommodations, the amount of {{convert|48|in|mm|adj=mid|-diameter}} welded steel pipeline between the pipe stations and the end of the line is {{convert|800.3|mi|km}}, while the linear distance between the Prudhoe Bay and Valdez station endpoints is {{convert|639.34|mi|km}}.<ref name="Facts4">Facts, p. 4</ref> The pipeline crosses 34 major streams or rivers and nearly 500 minor ones. Its highest point is at [[Atigun Pass]], where the pipeline is {{convert|4739|ft|m}} above sea level. The maximum grade of the pipeline is 145%, at Thompson Pass in the Chugach Mountains.<ref name="Facts4"/> The pipeline was created in 40 and 60-foot (12.2 and 18.3-meter) sections. Forty-two thousand of these sections were welded together to make a double joint, which was laid in place on the line. Sixty-six thousand "field girth welds" were needed to join the double joints into a continuous pipeline.<ref>Facts, p. 72</ref> The pipe is of two different thicknesses: {{convert|466|mi|km}} of it is {{convert|0.462|in|cm}} thick, while the remaining {{convert|334|mi|km}} is {{convert|0.562|in|cm}} thick.<ref name="Facts, p. 43"/> More than 78,000 vertical support members hold up the aboveground sections of pipeline,<ref>Facts, p. 71</ref> and the pipeline contains 178 valves.<ref>Facts, p. 70</ref>

At the end of the pipeline is the [[Valdez, Alaska#Oil terminal|Valdez Marine Terminal]], which can store {{convert|9.18|Moilbbl|m3}} of oil across eighteen storage tanks.<ref>Facts, p. 66</ref> They are {{convert|63.3|ft|m}} tall and {{convert|250|ft|m}} in diameter. They average 85% full at any given time—{{convert|7.8|Moilbbl|m3}}.<ref>Facts, p. 68</ref> Three power plants at the terminal generate 12.5 megawatts each.<ref>Facts, p. 67</ref> Four tanker berths are available for mooring ships in addition to two loading berths, where oil pumping takes place. More than 19,000 tankers have been filled by the marine terminal since 1977.<ref>Alyeska Pipeline Service Co. [http://www.alyeska-pipe.com/pipelinefacts/MarineTerminals.html "Pipeline facts: Valdez Marine Terminal"], Alyeska-pipe.com. March 30, 2009. Accessed July 15, 2009. {{webarchive |url=https://web.archive.org/web/20090527042243/http://www.alyeska-pipe.com/pipelinefacts/MarineTerminals.html |date=May 27, 2009 }}</ref>