Standard Practice for Ultrasonic Examination of Turbine-Generator Steel Retaining Rings Angle beam examination, Back-reflection, Contact method, Generator, Immersion method, Longitudinal wave testing, Nondestructive testing, Reference-block, Reference-notch, Retaining rings, Shear wave testing, Steel forgings-alloy, Turbine, Ultrasonic apparatus, Ultrasonic couplants, Ultrasonic examination