The development of cracks and corrosion in pipelines could pose a potential hazard to the community and the pipeline industry. Particularly for buried or insulated pipelines, corrosion and other types of defects may remain invisible unless the pipe is physically excavated or the insulation layers are removed. In this regard, advanced guided wave techniques are rapidly growing due to the advantages that they offer over traditional direct assessment inspection methods.

To overcome the challenges associated with the use of conventional ultrasonic techniques, a non-contact laser-based non-destructive evaluation system is proposed in this research work. Compared to conventional ultrasonic transducers, a laser-based technique remains functional at elevated temperatures and can result in high-resolution damage visualization. Using the laser Doppler vibrometer as the ultrasonic detection subsystem, and the pulsed Nd:​YAG laser for the ultrasonic generation, a complete non-contact ultrasonic system was implemented. The pulsed laser heats the surface of the specimen, and as a result, thermal and ultrasonic waves are generated in the structure. A reliable numerical model was created using the finite element analysis. The numerical results were validated with experiments in the time and frequency domains.

The application of a Nd:​YAG laser for ultrasonic wave generation was limited due to a lack of repeatability in the signals and low signal-to-noise ratio and potential damages to the surface. Instead, a piezoelectric transducer in combination with the laser Doppler vibrometer was used to enhance defect identification in aluminum plates. The results show that the proposed method can successfully identify the location and the approximate shape of hidden defects.