Residual stress mapping in a steam turbine disk using the L{sub CR} ultrasonic technique

Circumferential residual stresses in the rim of a steam turbine disk are evaluated using the L{sub CR} (critically refracted longitudinal wave) technique. Further development of the technique will enable an inspector to nondestructively determine the presence of unfavorable circumferential stresses in turbine disks. The effectiveness of the technique was evaluated with stresses mechanically induced in the disk by transverse loading and by removing a rim section. Strain gage and X-ray diffraction data confirmed the character of the stress fields evaluated by the L{sub CR} technique. Differences between L{sub CR} results and those from the other techniques are attributed to the X-ray diffraction and strain gage techniques being surface measurements, while the L{sub CR} wave speeds are affected by the stress gradient below the surface of the part.