How Do Pipelines Work?

Different types of pipelines

There are two general types of energy pipelines – liquid energy pipelines and gas pipelines.

The U.S. pipeline network is a highly integrated transmission and distribution grid that can transport energy products to and from nearly any location in the lower 48 states and Alaska. There are more than 2.6 million miles of natural gas pipelines and roughly 230,000 miles of liquids pipelines in the United States. Despite significant increases in both pipeline mileage and barrels delivered from 2016 to 2022, total incidents as well as those incidents impacting people and the environment have fallen.

Within the liquid pipeline network, pipes may transport crude oil, carbon dioxide, natural gas liquids, and refined products. Crude oil pipelines are subdivided into gathering lines and transmission lines.

Gathering Lines

Gathering lines are very small pipelines (usually 2 to 12 inches in diameter) that operate at relatively low pressures and flow rates and are used to transport crude oil or natural gas from the production site (the wellhead) to a central collection point.

Crude Pipelines

Cross-country crude oil transmission pipelines (or trunk lines) are larger (usually 12 to 24 inches in diameter) and transport crude oil from producing areas to refineries. There are approximately 84,000 miles of crude oil system lines in the United States that connect regional markets. There are also a few very large trunk lines in the United States like the Trans-Alaska Pipeline System, which is 48 inches in diameter.

Refined Product Pipelines

Refined product pipelines carry refined petroleum products like gasoline, jet fuel, home heating oil and diesel fuel. These pipelines vary in size from relatively small (12 inches in diameter) to much larger (42 inches in diameter). There are approximately 64,000 miles of refined product pipelines nationwide.

Product pipelines deliver petroleum products to large fuel terminals with storage tanks that are then loaded into tanker trucks. Trucks cover the last few miles to make local deliveries to gas stations and homes. Major industries, airports and electrical power generation plants are supplied with refined products directly by pipelines.

Natural Gas Liquids (NGL) Pipelines

NGL pipelines transport products such as propylene, propane, ethane, and liquified gas often used for manufacturing. These products power a number of modern comforts, including propane’s use as a common home heating fuel and ethane as a feedstock for plastics. These pipelines also vary in diameter, and there are over 75,000 miles of these lines in the U.S.

Carbon Dioxide Pipelines

Pipelines may also carry carbon dioxide from areas of capture to storage or utilization sites, including depleted reservoirs or aquifers. There are over 5,300 miles of carbon dioxide pipeline in the U.S., largely concentrated in the Gulf Coast and Southwest regions. CO2 pipelines have been safely operating in the U.S. for more than 50 years with an established record of performance and no fatalities associated with CO2 pipeline transportation. Our nation’s energy transition may require further buildout of low carbon energy infrastructure, including carbon dioxide pipelines, to meet energy and environmental demands in the coming decades.

Gas Pipelines

The natural gas pipeline system is organized somewhat differently than liquid pipeline systems. Natural gas is delivered directly to homes and businesses through distribution pipelines. Natural gas can contain natural gas liquids (NGL) when produced. Processors remove water, NGLs, and impurities from the natural gas stream to make the natural gas suitable for sale.

Regulators classify hydrogen as a gas when transported in pipelines. In the state of California, regulators have set a blend limit of 20% hydrogen by which pipelines must thereafter retrofit compressors, coatings, etc. to avoid leakage and pipeline embrittlement.

Natural gas and NGLs travel on separate pipeline systems until they reach their end users. There are over 2.3 million miles of natural gas distribution pipeline and over 300,000 miles of transmission pipeline.

What is commissioning?

After construction, pipelines undergo a series of tests before they are commissioned or placed in service. This “pre-commissioning” phase may include pipeline cleaning to remove any debris and hydrotesting, where the pipeline is filled with water at a pressure above the normal operating pressure to detect leaks. Pipeline coatings are also inspected.

Pipeline systems include pumps, storage tanks, and other associated infrastructure needed to make pipelines work. Pump stations are strategically located along a pipeline to safely boost internal pipeline pressure to keep crude oil and other liquids moving through the pipeline system. In gas pipeline systems, compressor stations are placed at intervals to keep the gas flowing smoothly to its destination. Storage tanks on each end of the liquid pipeline can temporarily store and/or receive shipped product.

What is batching?

Many liquid petroleum pipelines transport different types of products in the same pipeline. To do so, the pipeline operator sends different products in “batches.” For example, an operator might send gasoline for several hours, and then switch to jet fuel, before switching to diesel fuel. The process of tracking the customer’s batch or product through the pipeline is done through scheduling. Once the product has been scheduled and transported, a ticket shows the type of product transported, the amount, transportation origination, and destination points, as well as the owner.

Throughout the process, the product is measured at the receipt point in the pipeline and again upon delivery to document the amount of product moved from point A to point B.