A Review on Inspection Methods of Sewer Pipelines

Pipelines are widely used in transporting large quantities of water and sewage over long distances. These valuable infrastructures attract public attention only when they fail. The quantitative and early detection of defects in sewer pipelines is very important in order to avoid severe consequences. In many countries, sewer pipeline inspection is usually carried out using CCTV (Closed-Circuit TV) cameras and off-line human surveys through raw image assessment for failure identification. CCTV-based techniques have some limitations that restrict their implementation. One of the disadvantages of CCTV-based techniques is the lack of visibility in the interior of the pipes. The other disadvantage of CCTV-based techniques is the poor quality of the obtained imagesbecause of difficult lighting conditions. In consequence, CCTV-based techniques can only detect gross defects reliably. In recent decades, thermography, microwave, laser, and sonar-based techniques have been proposed to complement the conventional CCTV-based technique and to improve inspection results. Also, new inspection devices employing multiple sensors and being capable of carrying out remote sewer inspection tasks have been proposed. This paper presents an overview of the conventional and novel inspection technologies for sewer pipelines. Furthermore, different types of robots for in pipe inspection tasks are discussed