Pipelines

The nation’s network of more than 2.5 million miles of pipeline is largely regulated by the Department of Transportation’s (DOT) Pipeline and Hazardous Materials Safety Administration (PHMSA) and state entities. Part of this network consists of more than 200,000 miles (estimated) of onshore "gathering" pipelines, which transport hazardous liquid and natural gas products from wells to processing facilities and to larger transmission pipelines. Many of these gathering pipelines, however, have not been subject to PHMSA regulation because they are generally located away from population centers and operate at low pressures.

Pipelines transport roughly two-thirds of domestic energy supplies throughout the United States. These pipelines carry hazardous liquids and natural gas from producing wells to end users (residences and businesses). Within this nationwide system, there are three main types of pipelines.

Gathering pipelines

Gas gathering pipelines collect natural gas from production areas, while hazardous liquid gathering pipelines collect oil and other petroleum products. These pipelines then typically transport the products to processing facilities, which in turn refine and send the products to transmission pipelines. According to PHMSA officials, traditionally, gathering pipelines range in diameter from about 2 to 12 inches and operate at pressures that range from about 5 to 800 pounds per square inch (psi). These pipelines tend to be located in rural areas but can also be located in urban areas. PHMSA estimates there are 200,000 miles of gas gathering pipelines and 30,000 to 40,000 miles of hazardous liquid gathering pipelines.

Transmission pipelines

Transmission pipelines carry hazardous liquid or natural gas, sometimes over hundreds of miles, to communities and large-volume users (e.g., factories). For natural gas transmission pipelines, compression stations located periodically along the pipeline maintain product pressure. Similarly, pumping stations along hazardous liquid transmission pipelines maintain product flow. Transmission pipelines tend to have the largest diameters and pressures of any type of pipeline, generally ranging from 12 inches to 42 inches in diameter and operating at pressures ranging from 400 to 1440 psi.

Distribution pipelines

Gas distribution pipelines continue to transport natural gas to residential, commercial, and industrial customers, splitting off from transmission pipelines. These pipelines tend to be smaller, sometimes less than 1 inch in diameter, and operate at lower pressures—0.25 to 100 psi. PHMSA has estimated there are roughly 2 million miles of distribution pipelines, most of which are intrastate pipelines. There are no hazardous liquid distribution pipelines. For the purposes of this report, we use the term transmission pipeline to refer to both hazardous liquid and natural gas pipelines carrying product over long distances to users.

GAO: "PIPELINE SAFETY, Collecting Data and Sharing Information on Federally Unregulated Gathering Pipelines Could Help Enhance Safety," March 2012