Pipelines are used to transport a number of substances including natural gas, fuels, hydrogen, water, beverages, and petroleum. Most people are familiar with the Trans Alaska Pipeline System (TAPS), but may be less well acquainted with the other 55,000 miles of crude oil trunk lines running throughout the United States. This number does not account for the estimated 30,000 to 40,000 miles of “gathering” lines that connect oil production sites to main trunks. The Pan-European Oil Pipeline, which is proposed to run from Romania to Italy, would connect with the Transalpine Pipeline that continues to Germany. If the extension is completed, the total length of the pipeline would reach 2608 kilometers.
Oil pipelines are generally divided into two basic sections called trunks and gathering lines. Trunks range in size from 20 to 60 centimeters in diameter while gathering lines range from 5 to 15 centimeters in diameter. Even at these large diameters, it takes a substantial amount of force to propel oil through a pipeline.
Propulsion and Speed of Delivery
In general, oil is propelled through the use of centrifugal pumps. Pumps are located at the originating station of the line and then at 30 to 160 kilometer intervals along the line. The length of the pipeline, type oil being transported, capacity requirements, and topography of the land all determine the spacing of the pumps. Most pumps are driven by electric motors, but diesel engines or gas turbines may be used on oaccasion. Computers are used to remotely control the pumps as well as other aspects of pipeline operation.
Most pipelines are operated and monitored 24 hours a day, every day of the year. They are capable of moving the oil at speeds of 5 to 13 kilometers per hour. Transport speed depends upon the diameter of the pipe, the pressure under which the oil is being transported, they topography of the terrain, and viscosity of the oil. At average speeds, it takes 14 to 22 days to move oil from Huston, Texas to New York City.
The particular type of crude oil that can be pumped through a given pipeline is dependent on the characteristics of a line such as length and diameter. In general, batch operation or sequencing is used to transport one refined product or crude oil grade after another. The interface between two products is referred to as the transmix, and it must be reprocessed before use.
Batch processing gets its name from the fact that different pipelines require different batches or volumes of petroleum be transported at a given time. This is done to reduce cost and to ensure that there is as little transmix as possible.