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There are two types of oil pipeline: crude oil pipeline and product pipeline. While the former carries crude oil to refineries, the latter transports refined products such as gasoline, kerosene, jet fuel, and heating oil from refineries to the market. Different grades of crude oil or different refined products are usually transported through the same pipeline in different batches. Mixing between batches is small and can be controlled. This is accomplished either by using large batches (long columns of the same oil or product) or by placing an inflated rubber sphere or ball between batches to separate them. Crude oil and some petroleum products moving through pipelines often contain a small amount of additives to reduce internal corrosion of pipe and decrease energy loss (drag reduction). The most commonly used drag-reducing additives are polymers such as polyethylene oxides. Oil pipelines almost exclusively use steel pipe without lining but with an external coating and cathodic protection to minimize external corrosion. They are welded together and bent to shape in the field.
Some of the oil pipelines constructed in the United States include the “Big Inch” and “Little Big Inch” pipelines built during World War II to counter the threat of German submarine attacks on coastal tankers; a large product pipeline from Houston, Texas, to Linden, N.J., built by the Colonial Pipeline Company in the 1960s to counter the strike of the maritime union; and the Trans-Alaska Pipeline built to bring crude oil from the North Slope to Prudhoe Bay for meeting the challenge posed by the Arab oil embargo of 1973.
Offshore (submarine) pipelines are needed for transporting oil and natural gas from offshore oil wells and gas wells to overland pipelines, which further transport the oil to a refinery or the gas to a processing plant. They are more expensive and difficult to build than overland pipelines. Offshore construction usually employs a barge on which pipe sections are welded together and connected to the end of the overland pipe. As more sections are welded to the pipe end, the barge moves toward the oil or gas field, and the completed portion of the pipe is continuously lowered into the sea behind the barge. Construction progresses until the barge has reached the field and the pipe is connected to the oil or gas well. In deep seas with large waves, ships instead of barges are used to lay the pipe. The most notable offshore oil pipeline is one linking the British North Sea oil fields to the Shetland Islands.
Gas pipelines
Practically all overland transportation of natural gas is by pipeline. To transport natural gas by other modes such as truck, train, or barge would be more dangerous and expensive. While gas collection and transmission lines are made of steel, most distribution lines (i.e., smaller lines connecting from the main or transmission lines to customers) built in the United States since 1980 use flexible plastic pipes, which are easy to lay and do not corrode.
The United States operates the world’s largest and most sophisticated natural gas pipeline network. Most other nations in the world also use natural gas and have natural gas pipelines.
Pipelines for transporting other fluids
Pipelines have been built to transport many other fluids (liquids and gases). For instance, liquid fertilizers are often transported long distances via pipelines. The mixture of oil and natural gas coming out of a well must be transported as two-phase flow by pipelines to processing facilities before the oil can be separated from the gas. Liquefied natural gas (LNG) transported by ships (tankers) also requires short pipelines to connect the ships to onshore storage tanks. Pipelines as long as 180 miles have been built in the United States to transport carbon dioxide to oil fields for injection into reservoirs to enhance oil recovery. Finally, on a smaller scale, most chemical, food, and pharmaceutical plants use pipe to transport various liquids and gases within the plants. When such fluids are corrosive or cannot tolerate impurities, the pipe must be of inert materials.
Slurry pipelines
Slurry is the mixture of solid particles and a liquid, usually water. The particles can range in size from greater than four inches in equivalent diameter to less than one-thousandth of an inch. When the solid particles in the liquid are small and finely ground, the mixture is called fine slurry, and when the particles are larger, it is called coarse slurry. Traditionally, the mining industry has employed pipelines to transport mine wastes and tailings in slurry form to disposal sites, using water as the fluid. Dredging also uses slurry pipeline. The sand, gravel, or soil dredged from a river is often pumped with water through a pipeline to a construction site for a distance of up to a few miles.
In general, when pipelines are used to transport coarse slurry, the slurry velocity must be relatively high in order to suspend the solids. Such slurry transport is very abrasive to the pipe and the pump, and the power consumed is high. Consequently, coarse-slurry pipelines are economical only over relatively short distances, normally not more than a few miles. An important application of coarse-slurry pipeline is “concrete pumping,” in which concrete is pumped from a parked truck through a portable steel pipe attached to a side boom to reach rooftops and bridge decks. It is a method of conveying and laying concrete employed increasingly in construction.
Long-distance transport of solids by slurry pipeline must use relatively fine slurry. Existing coal-slurry pipelines carry fine slurry consisting of about 50 percent coal and 50 percent water by weight. The solid is first pulverized and mixed with water to form a paste. The slurry then enters a mixing tank, which contains one or more large rotating wheels or propellers that keep the particles uniformly mixed. Next, the slurry enters the pipeline. Special plunger or piston pumps are used to pump the slurry over long distances. The United States pioneered the coal-slurry pipeline technology. The first long-distance coal-slurry pipeline was constructed in Ohio in 1957. The line was discontinued later when the competing railroad agreed to lower its freight rate. The pipeline was then mothballed for years and used as a leverage against rail rate increases. It was said to have prompted railroads to modernize and become more competitive, introducing the concept of the unit train, which employs about 100 cars to haul coal nonstop from mines to power plants.
The world’s longest coal-slurry pipeline is the Black Mesa pipeline in the United States. Built in 1970, this 18-inch pipeline transports 4.8 million tons of coal per year from Black Mesa, Ariz., to southern Nevada, over a distance of 273 miles. This coal pipeline has been highly successful. Many other long-distance slurry pipelines exist in the world to transport coal and other minerals such as iron concentrate and copper ore.
Pneumatic pipelines
Pneumatic pipelines, also called pneumo transport, transport solid particles using air as the carrier medium. Because air is free and exists everywhere, and because it does not wet or react chemically with most solids, pneumo transport is preferred to hydro transport for most cargoes wherever the transportation distance is short. Owing to high energy consumption and abrasiveness to pipe and materials, pneumatic pipelines are usually adopted for distances not more than a few hundred feet or metres. Large-diameter pneumatic pipelines can be used economically for longer distances, sometimes more than a mile or a kilometre.
Pneumatic pipelines are employed extensively throughout the world in bulk materials handling, and hundreds of different cargoes have been transported successfully. Common applications include the loading of grain from silos or grain elevators to trucks or trains parked nearby, transport of refuse from collection stations to processing plants or from processing plants to disposal sites, transport of cement or sand to construction sites, and transport of coal from storage bins to boilers within a power plant.
There are two general types of pneumatic pipelines. The first employs suction lines, which create a suction or vacuum in the pipe by placing the compressor or blower near the downstream end of the pipe. The line operates like a vacuum cleaner. The second type is pressure lines, which have compressors or blowers located near the upstream end. This creates a pressure in the line that drives the air and the solids through the pipe. Pressure lines are used for longer distances and in places where solids concentrated at one location are transported to several separate locations using a single blower or compressor. In contrast, suction lines are more convenient for shorter distances and in places where solids from several locations are to be transported to a common destination by means of a common blower or compressor.
In addition to the pipe and blower, a pneumatic pipeline system also must have a tank or hopper connected near the pipeline inlet to feed solid particles into the pipeline and a tank near the pipeline outlet to separate the transported solids from the airstream. The exhaust air also must be filtered to prevent air pollution.
Combustible solids such as grain or coal transported pneumatically through pipe, if handled improperly, can cause fire or even explosion. This is due to the accumulation of electric charges on fine particles transported pneumatically. Prevention of such hazards can be accomplished by using metal rather than plastic pipes; by grounding the pipe, valves, and other fixtures that accumulate charges; by cleaning the interior of the pipe to rid it of dust; and by increasing the moisture of the air used for pneumatic transport.
Capsule pipelines
Capsule pipelines transport freight in capsules propelled by a fluid moving through a pipeline. When the fluid is air or another gas, the technology is called pneumatic capsule pipeline (PCP), and, when water or another liquid is used, it is termed hydraulic capsule pipeline (HCP). Owing to the low density of air, capsules in PCP cannot be suspended by air at ordinary speeds. Instead, the capsules are wheeled vehicles rolling through pipelines. In contrast, because water is heavy, the capsules in HCP do not require wheels. They are both propelled and suspended by water under ordinary operational speeds. HCP systems are operated normally at a speed of 6 to 10 feet per second (1.8 to 3 metres per second), whereas the operational speed of PCP is normally much higher—20 to 50 feet per second. Owing to high frictional loss at high velocity, PCP consumes more energy in operation than HCP.
PCP has been in use since the 19th century for transporting mail, printed telegraph messages, machine parts, cash receipts, books, blood samples (in hospitals), and many other products. Since 1970, large wheeled PCP systems have been developed for transporting heavy cargo over relatively long distances. The largest PCP in the world is LILO-2 in the republic of Georgia, which has a diameter of 48 inches and a length of 11 miles. The system was built for transporting rock.
In contrast to the long history of PCP, the technology of HCP is still in its infant stage. HCP was first considered by the British military for transporting war matériel in East Asia during World War II. The concept received extensive investigation in Canada at the Alberta Research Council during 1958–75. Interest in this new technology soon spread to many other nations. In 1991, the United States established a Capsule Pipeline Research Center at the University of Missouri in Columbia, jointly funded by industry and government.
A new type of HCP being developed is coal-log pipeline (CLP), which transports compressed coal logs. The system eliminates the use of capsules to enclose coal and the need for having a separate pipeline to return empty capsules. Compared with a coal-slurry pipeline of the same diameter, CLP can transport more coal using less water.
Capsule pipelines of large diameter (greater than seven feet) can be used to transport most of the cargoes normally carried by trucks or trains. In both Europe and the United States, large-diameter capsule pipelines (mostly PCPs) have been proposed for intercity freight transport in the 21st century. Proponents of such projects point out that such underground freight pipeline systems not only allow land surface to be used for other purposes but also reduce the number of trucks and trains needed, which in turn reduces air pollution, accidents, traffic jams, and damage to highway and rail infrastructures caused by the high traffic volume.
