One way to get oil and gas from its source to a refinery and then from a refinery to the people who use the gasoline and other products made there is with a pipeline. Oil pipelines are made from steel or plastic tubes with inner diameter typically from 4 to 48 inches (100 to 1,200 mm) and can be as short as the length from a production facility to a nearby storage tank or as long as several thousand kilometres. Pipelines may also be used to get oil or gas from its source to a terminal, a special facility where ocean-going tankers fill up for their journeys across open waters.
Pipelines can be built above land, under land or under water*. When a pipeline runs through an environmentally sensitive area or close to a city or town, burying it is one way to minimize the likelihood and impact of potential accidents. Most pipelines are typically buried at a depth of about 3 to 6 feet (0.91 to 1.8 m). To protect pipes from impact abrasion and corrosion, a variety of methods are used. These can include wood lagging (wood slats), concrete coating, rockshield, high-density polyethylene, imported sand padding and padding machines.
Oil pipelines are generally the most economical way to transport large quantities of oil, refined oil products or natural gas over land. Where the alternative of sea going vessels is not available, for example when the oil is produced in a land locked country, then the alternatives to pipelines are very much more expensive.
The oil or gas in a pipeline is kept in motion by a system of pump stations built along it and usually flows at speed of about 1 to 6 metres per second (3.3 to 20 ft/s). Workers walk the length of the pipeline regularly to check for any signs of potential leaks or other complications. Usually in multi-product pipelines there is no physical separation between the different products. Some mixing of adjacent products occurs, producing interface, also known in the industry as « transmix ». At the receiving facilities this interface is usually absorbed in one of the products based on pre-calculated absorption rates. Alternately, transmix may be diverted and shipped to facilites for separation of the commingled products.
For natural gas, pipelines are constructed of carbon steel and vary in size from 2 to 60 inches (51 to 1,500 mm) in diameter, depending on the type of pipeline. The gas is pressurized by compressor stations and is odourless unless mixed with a mercaptan odorant where required by a regulating authority.
Pipelines have the major disadvantages that they are vulnerable to sabotage, they require significant capital cost and time to build, and they are the least flexible option. Where a pipeline crosses a number of countries, the geopolitical problems can be very significant.
* Although pipelines can be built under the sea, that process is economically and technically demanding, so the majority of oil at sea is transported by tanker ships