A multi-helical ultrasonic imaging approach for the structural health monitoring of cylindrical structures

In the past few years, several efforts have been made to combine guided ultrasonic waves and imaging algorithms such as tomography for detecting and locating damage in complex structures. In this article, we introduce a multi-helical ultrasonic imaging approach for the structural health monitoring of cylindrical structures. An array of permanently installed piezoelectric transducers is used to generate and receive high-order helical guided waves around the cylindrical structure to artificially increase the ray density/resolution without increasing the number of sensors. A probabilistic-based imaging algorithm is used to identify metal loss defects. Experimental tests are carried out on a steel pipe instrumented with six piezoelectric transducers to validate the proposed approach. Three thickness recesses simulating corrosion are considered. Results demonstrate the efficacy of the proposed approach by identifying the simulated damage at the correct locations and qualitatively monitoring damage growth. No attempt is made in this study to quantify the extent of thinning.