Strategies for pipeline inspection using mobile robots

Continuous non-destructive monitoring of large-scale pipelines is extremely challenging with traditional manual inspections. In this paper, we explore possible strategies that a collection of inspection robots could adopt to address this challenge. We envision the continuous inspection of a pipe performed by multiple robots or a single robot that combines measurements from multiple locations. The robots use guided ultrasonic waves to detect defects and interrogate their locations. The experimental inspection works were performed on a 3-meter-long steel pipe with multiple defects. The whole inspection process was divided into a defect detection stage and a defect localisation stage. In the detection stage the receiver operating characteristic defines a threshold to find a detection zone in which a defect is thought to be present. In the localisation stage, further six measurements arranged in a pentagon with a central measurement point are made to locate the defect within this zone to a certain accuracy. We also discussed the effect of sensor misposition on defect location accuracy using Monte Carlo simulations. As predicted from simulation, seven of nine defects on the pipe were detected and located with reasonable defect location accuracy. This accuracy was further improved by using additional measurements. A methodology by which mobile robots can inspect large pipelines has been described and demonstrated on detecting and localising multiple defects on a 3-mm-long steel pipe. This will benefit a workable approach to the use of autonomous (or semiautonomous) mobile robots for the inspection of large structures that is just the beginning of exploration in the area.