Pipes are hollow tubular strucutre used in homes, businesses, drainage systems, and more, to transport water, gas, waste, or other substances from one location to another. Pipelines have pumps, valves, and control systems that allow people to manipulate the flow of the substances that are being transported.

In early history, pipes were made of materials such as lead or stone. Today, pipes are typically made of steel, iron, aluminum, plastic, or clay. Some are as small around as 1.02 centimeters (0.405 inches), while other, large pipes are up to nine meters (30 feet) across.

Pipeline systems are, in most cases, buried underground. Because they often carry environmentally harmful substances, such as waste or oil, they must be carefully constructed of the materials most appropriate for the substance being transported. Pipeline failures, such as corrosion, can lead to serious pollution or explosions. Accidents like these can continue to harm the surrounding environment and wildlife for decades after a leak or break.

In some places, it is impossible to bury pipelines completely underground. An example of an aboveground pipeline is the Trans-Alaska Pipeline, which began in 1975 after the discovery of the United States’ largest oil strike, at Prudhoe Bay north of Alaska, in 1968. The pipeline travels 1,270 kilometers (789 miles) south to Valdez, Alaska, where oil is placed on tankers for shipment. Today, the pipeline carries around 500,000 barrels of oil a day.