Practical Long Range Guided Wave Inspection - Applications to Pipes and Rail

The inspection of large structures using conventional ultrasonic bulk wave techniques is slow because scanning is required if the whole structure is to be tested. Ultrasonic guided waves potentially provide an attractive solution to this problem because they can be excited at one location on the structure and will propagate many metres. However, guided wave testing is complicated by the presence of many possible wave modes, most of which are dispersive. These guided wave characteristics offer a wealth of opportunities for the extraction of information about the structure, but it is crucial to manage this complexity if the test is to be useable in industrial practice. This paper concentrates on long range testing using frequencies below 100 kHz. The progress from research work to a robust, commercial pipe testing system will be discussed, together with more recent research on applications to plates and railroad rails. The paper concludes with a discussion of future research opportunities.