Guided wave based-occupancy grid robotic mapping

Asset inspection of large structures such as storage tanks in the oil, gas and petrochemical industry is challenging, either requiring labour-intensive manual measurements or using robotic deployment to make the measurements. Current robotic systems employ point-by-point scanning, which is time-consuming. Using guided waves for such inspections is attractive as they provide a mechanism for monitoring the inaccessible areas and simultaneously providing structural location data to speed up the inspection process. In this research, shear horizontal (SH) guided waves generated by electromagnetic acoustic transducers (EMATs) are used to screen a large area using a crawler. EMATs with 22 mm wavelength are used to generate the first two SH modes: a non-dispersive SH0 and highly dispersive SH1 on a 10 mm thick steel sample. Previously, we have demonstrated the feasibility of guided wave-based occupancy grid mapping (GW-OGM) for mapping a structure's edges. In this work, the GW-OGM technique is generalised to identify and estimate the location of a flat bottom hole in a pitch-catch mode. The simulation and empirical data demonstrate that the location of damage can be identified as the robot navigates on the component, with full coverage. Moreover, the simulated data are in good agreement with the experimental results on the generation of SH wave modes.