The monitoring approaches and non-destructive testing technologies for sewer pipelines

Sewage pipe deterioration has been one of the factors causing huge asset losses and urban hazards worldwide. For more efficient and reliable management, a variety of monitoring and non-destructive testing techniques has been developed for defect inspection and condition assessment of sewer pipes. In the present paper, the monitoring approaches of sewage pipes in the form of operational monitoring, structural monitoring, and durability monitoring are outlined. The fundamentals and features of various non-destructive testing (NDT) techniques for different target detect locations are presented. The stereo vision, light detection and ranging (LiDAR), and laser 3D scanning technologies that might serve to architect the digital twin of the pipeline are also described. What's more, the capabilities and limitations of these technologies are discussed and summarized in tables. Some possible visions for the development of inspection and quantitative evaluation of sewage pipes are also discussed. In practice, it is suggested that visual inspection techniques are the most feasible for the evaluation of underground pipes. In terms of quantitative and automated evaluation, visual inspection robots equipped with stereo vision or laser 3D scanning technology are the most promising.