Ultrasonic thickness measuring in-pipe robot for real-time non-destructive evaluation of polymeric spray linings in drinking water pipe infrastructure

Drinking water pipelines are mainly underground and exposed to corrosion. Polymeric spray liners are used as an economical renewal method to mitigate the consequences of internal corrosion of pipelines and prolong their useful service life by many water utilities around the globe. The quality assurance of such applications is currently limited to closed-circuit television (CCTV), which only provides visual information. As part of the Australian government-funded, thirty-four partner multi-million dollar project (CRC-P: Smart Linings for Pipes and Infrastructure project), this work focuses on measuring the post-application thickness of spray liners in pipes. In this article, we report the innovative development of in-pipe robotic sensing suite that leverages ultrasonic sensing to continuously inspect the thickness of the spray linings through non-destructive measurements. The ultrasonic sensor was calibrated by fabricating laboratory test sample made from polymeric spray linings. Continuous uninterrupted coupling was achieved through a custom designed mechanism which was proven to be reliable through field deployments. Extensive lab tests were conducted to validate the sensor measurements with the benchmark measurements producing results with sub-millimeter accuracy. Following lab validations, field trials in buried pipe assets of Sydney Water were conducted for pipe lengths over 35 $m$, and the field test results show the robotic system is capable of reliably providing accurate spray liner thickness along the pipeline in real-time through non-destructive evaluation.