Localization, Mapping, Navigation, and Inspection Methods in In-Pipe Robots: A Review

Pipelines are backbone of the transportation of gases and liquids such as oil, gasoline, water, and sewage. However, pipelines are constantly aging and sustaining damage, which may result in significant resource loss and environmental contamination. Pipelines must be inspected and maintained on a regular basis for effective functioning and to avoid cost overrun. Due to the fact that pipes are often located underground and they have different sizes and configurations, inspection including condition assessment, leak detection, and fluid quality monitoring of pipelines are challenging. For this purpose, in-pipe robots have shown promising solutions to reach the inaccessible parts of pipeline networks. In this paper, we first categorize the mechanical systems of in-pipe robots. Then, we review four missions performed by these robots, including localization, mapping, navigation, and inspection, along with the core methods used in each mission. Further, since image processing is a common and important approach to accomplish all the mentioned missions, we decided to dedicate a separate section for reviewing comprehensive categorization of image processing techniques. We also provide the list sensors used in in-pipe robots classified by the mission and the method of use.