Multi-mode tandem ultrasonic technique for tube inspection

Tubes used in aerospace and petrochemical industries for fluid transport and are subjected to high temperature and stress levels. Over a period of time, these tubes are expected to degrade owing to different creep mechanisms, sometimes leading to catastrophic failure. The damages ranging from formation of isolated cavities to presence of micro cracks are expected as result of creep mechanism. The existing method of ultrasonic inspection involves the generation of a longitudinal wave at appropriate angle of incident in order for the mode to travel across the chord of the tube and then received using an identical transducer. This technique has been shown to be un-reliable due to the variations in the type and orientation of the cracks. Here, a new multi-mode tandem configuration ultrasonic technique, that utilizes the two bulk wave modes in a tandem configuration, i.e. both Longitudinal and Transverse modes propagating along the chord of the tube, has been employed in order to improve the reliability of inspection. The transverse waves were found to be more sensitive to flaw orientations that were more circumferential. Eight different configuration of inspection were carried out using the multi mode inspection technique. Experimental and FEM model validate improved sensitivity and consequently validate the reliability of the tandem approach.