Robots called pigs crawl through oil pipelines to scrape and inspect them
Crude oil carries paraffin wax, and in cold climates it builds up inside pipelines. Operators clear it by launching devices called pigs, also known as scrapers or go-devils, which ride the flow from one station to the next. Smart pigs go further, recording dents, cracks and corrosion so crews can find weak spots before they leak.
Pipelines are the cheapest way to move large amounts of oil or gas overland. In 2014 shipping crude by pipe cost about 5 dollars a barrel, against roughly 10 to 15 by rail, and trucks cost more still because they need so many drivers; a finished pipeline employs about 1 percent as many people as trucking. In the United States, 70 percent of crude and petroleum products travel by pipe, and in Canada the share for gas and petroleum products reaches 97 percent.
The idea started small. In the 1860s the Oil Transport Association laid a wrought-iron pipe just 2 inches wide over 6 miles, linking a Pennsylvania oil field to a railway station at Oil Creek. In 1944, Operation Pluto ran lines under the English Channel that supplied an estimated 8 percent of the petroleum used by the Allies on the Western Front after the Normandy landings. China's first long-distance oil line, 147 kilometres from the Karamay field to the Dushanzi refinery, opened on 10 January 1959.
Today the world has around 2.19 million kilometres of trunk and transmission lines, and the United States alone accounts for 65 percent of them. Oil lines range from 4 to 48 inches across and are usually buried about 3 to 6 feet down, wrapped in concrete, plastic, sand or wooden slats and protected by sacrificial cathodes against corrosion. Pump stations push oil along; gas lines of carbon steel, up to 60 inches wide, rely on compressor stations instead. Natural gas has no smell, so regulators often require an odorant called mercaptan.
Almost any chemically stable fluid can go by pipe, from sewage and slurry to steam and even beer over short distances. Ethanol is harder: it corrodes pipes and absorbs water and impurities, so in the United States most of it still travels by rail.
Source: Pipeline
