A Natural Focusing Low Frequency Guided Wave Experiment for the Detection of Defects Beyond Elbows

Long range ultrasonic guided wave inspection is advancing rapidly and is quite commonplace today. Benefits of using longitudinal or torsional modes are being established in special circumstances of improved sensitivity, resolution, or penetration power. The possibility of inspection under insulation, coatings, or with water filled pipes or around elbows is possible. Detection of defects beyond a pipe elbow is difficult for axisymmetric wave impingement onto the elbow. For nonaxisymmetric input to the elbow region, however, via partial loading around the circumference, natural focusing occurs because of angular profile variation around the circumference of the pipe. Sample computations of possible angular profiles are illustrated. An experiment is also reported here to demonstrate this inspection process.