The main risk posed by an oil or gas pipeline is the existence of a spill or a leakage that threatens to cause an environmental disaster, not to mention the risk of an explosion. Pipeline systems are often located underground or run for many kilometres where access roads are restricted, the surrounding nature is not attained and access to pipelines is incredibly difficult or impossible. It is not humanly possible to visually check everything and fitting built-in measuring systems (pressure meters, flow meters) is financially demanding and not too reliable because it does not cover all risky places. A common solution to this problem is using aircraft to visually inspect. However, due to the costs of employing a pilot, purchasing an airplane, and fuel some companies are seeking alternative inspection methods. The number one solution for keeping costs down and maintaining high quality inspections is the use of a drone.  Drone based monitoring is increasingly viable because sensor technology is advancing at a sufficient pace to allow small, yet powerful sensors to be fitted to the drone. One of the main benefits of using drones for this analysis is that they can be programmed to cover large areas in a systematic way, as well as get to difficult to reach areas.

https://www.huffingtonpost.com/entry/using-drones-to-monitor-oil-pipelines_us_59390907e4b014ae8c69ddd4

Pipeline inspection with thermal diagnostics