How Do Pipelines Work?

Key Takeaways

  • Gathering lines transport oil and gas from the production site to a central collection point.
  • Transmission lines deliver oil and gas from these central collection points to refineries and processing centers across the country.
  • Transmission line carry different products, including crude oil, refined products, natural gas liquids and natural gas.

Different types of pipelines

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

The U.S. pipeline network is a highly-integrated transmission and distribution grid that can transport crude oil, petroleum products and natural gas to and from nearly any location in the lower 48 states and Alaska. There are more than 2.5 million miles of natural gas pipelines and 218,000 miles of liquids pipelines in the United States.

Within the liquid petroleum pipeline network, there are crude oil lines and refined product lines. Crude oil pipelines are subdivided in to 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 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 (the wellhead) to refineries. There are approximately 80,000 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 State like the Trans-Alaska Pipeline System, which is 48 inches in diameter.

The Trans-Alaska Pipeline System is one of the largest crude oil transmission lines in the US.

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 62,000 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 70,000 miles of these lines located in the U.S.

Stack of shiny metal steel pipes with flame

Natural 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.

Natural gas and NGLs then travel on separate pipeline systems until they reach their end users. There are over 2.2 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.

Before commissioning, a pipeline and all associated facilities are tested and 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 natural 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 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 actually transported, a ticket shows the type of product transported, the amount, transportation origination and destination points, and 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.