GUIDED-WAVE TUNING PRINCIPLES FOR DEFECT DETECTION IN TUBING

Dispersion diagrams for longitudinal modes and several flexural modes are given. A partial loading oblique incidence technique was introduce d for non-axisymmetric guided wave generation. Acoustic fields for par tially loaded generation of guided waves were obtained along a sample Inconel steam generator tube surface. The axial field and the circumfe rential fields were non uniform. Even though the acoustic field was mu ch more complicated than in the case of axisymmetric modes, the study of non-axisymmetric mode cannot be avoided; excitation of a single sym metric mode is often difficult due to limited access and transducer ef ficiency and there is also mode conversion after scattering from defec ts. For 100% inspection coverage of tubing and piping, three dimension al tuning (distance, frequency, and incident angle tuning), was employ ed. A single combination of incident angle, position, and frequency ma y miss defects in ''blind spots''. However, complete inspection covera ge of a whole cross sectional area over a certain distance of tubing w as successfully demonstrated through a multi crack detection experimen t by using the three dimensional tuning concepts. Also, the use of non -axisymmetric guided waves for a large distance inspection capability was successfully demonstrated.