Pipe inspection using guided acoustic wave sensors integrated with mobile robots

In this paper we propose an approach to inspect pipelines that can be applied for multiple robots or a single robot with integrated acoustical sensors with high resolution detection and good localization accuracy. The approach is demonstrated by the successful inspection of multiple defects on a steel pipe using manually manipulated guided acoustic wave sensors. The approach was divided into two stages: defect detection and localization. In the detection stage the receiver operating characteristic defines a detection amplitude threshold and a detection zone of a single sensor in which a reference defect (for example, randomly chosen 8.5 mm diameter through thickness circular hole) could be present and requested to screen. The size of this zone decides the sensor sampling pitch distance to ensure 100% detection coverage of an entire pipe. This leads to the successful detection of the reference and other defects. In the localization stage, for each sensor location showing defect detection, five further measurements were made to locate the defect within the detection zone and this led to measured defect location errors less than 30 mm for the reference defect that agrees well with predictions from Monte Carlo simulations. The density-based algorithm for discovering clusters was successfully used to identify and combine multiple measurements on the reference defect.