RESIDUAL-STRESS MAPPING IN A STEAM-TURBINE DISK USING THE L(CR) ULTRASONIC TECHNIQUE

Circumferential residual stresses in the rim of a steam turbine disk a re evaluated using the L(CR) (critically refracted longitudinal wave) technique. Further development of the technique will enable an inspect or to nondestructively determine the presence of unfavorable circumfer ential stresses in turbine disks. The effectiveness of the technique w as evaluated with stresses mechanically induced in the disk by transve rse loading and by removing a rim section. Strain gage and X-ray diffr action ata confirmed the character of the stress fields evaluated by t he L(CR) technique. Differences between L(CR) results and those from t he other techniques are attributed to the X-ray diffraction and strain gage techniques being surface measurements, while the L(CR) wave spee ds are affected by the stress gradient below the surface of the part.