Robert V. Falsetti

Ultrasonic Inspection of Acoustically “Noisy” Materials

Ultrasonic inspection of large gas turbine rotor forgings made of IN706 (40Ni-15Cr-Ti-Nb superalloy) is complicated by the material’s anisotropic and nonuniform acoustic properties. These properties stem from the intrinsically coarse grain structure of IN706 in forgings weighing up to 22,000 pounds and having axial and radial dimensions up to 20 inches and 90 inches, respectively. Although recent advances in the melting and forging processes have helped to improve the material’s microstructure, many characteristics still preside which make ultrasonic inspection a challenge. The inspection and signal processing techniques described herein compensate for variations in the acoustic properties that we have observed from forging to forging as well as within any given forging. These techniques may be applied to a wide variety of applications dealing with acoustically noisy materials with nonuniform acoustic characteristics.