You probably know that pipelines transmit oil or gas from location to location. Essentially, they get the materials to the point of consumption, but let's expand on this a little so we can grasp just how important smart pigs are for this hardy, but vulnerable infrastructure.
Pipelines are everywhere. You've probably passed over a buried pipeline many times and never knew it. Pipelines carry crude oil or natural gas over land. It used to be that oil sold by the barrel would be hauled by horse-drawn wagons to the railroad where they were transported for a longer journey. This is where we get our unit of measurement for the amount of oil being sold. One barrel these days equals roughly 42 gallons.
The picture seen here (and above) shows pieces of the Trans-Alaska pipeline. This is the most famous above-ground pipeline that runs 800 miles across Alaska to Valdez. It is raised simply because the permafrost causes some complications which ultimately meant that a buried pipeline was out of the question.
There are a series of different pipes that carry oil and gas from beginning to end that you could imagine is similar to a tree with roots, a trunk and branches. Oil pumped fresh from the ground is pumped into collector pipelines. From the collector pipelines they are pumped to field processing stations where larger pipes push the material to a main-line pipeline.
This main-line pipeline is most often a larger pipe and will carry the product to refineries many miles away. From here the refinery will pump the material through a series of smaller pipelines that divide into smaller branches until they reach distribution depots.
Why use pipelines to transport oil? Simply because it is still more energy efficient to transport through pipelines than it is by train or by truck.
This huge network of pipes is made of a very high-strength steel. These pipes naturally have corrosion over time, so pipes are coated with a special substance and wrapped in thick tape. Although it helps, this doesn't stop leaks from happening over time. This is why smart pigs are so important. The corrosion that takes place that the tape and preventative coatings can't stop can be detected and repaired effeciently with the use of these pigging devices.