High-Sensitivity, Immersion, Ultrasonic Testing of Steel Forgings

Present industry-wide standards covering ultrasonic inspections of forgings such as ASTM Recommended Practice for Ultrasonic Examination of Heavy Steel Forgings (A 388-80) specify the contact method of inspection. Sensitivity settings vary as to inspection technique—longitudinal or shear wave (straight or angle beam). Normally, the sensitivity is established using a back reflection or test sample technique in order to resolve equivalent flat-bottom hole (EFBH) sizes of 3.175 mm (0.125 in.) at the centerline or bore surface of the forging. The assumption is made that most indications will be oriented parallel to the direction of the longitudinal axis of cylindrical forgings and in a circumferential plane of ring forgings. On occasion, discontinuities occur in forgings that are different than normal, requiring changes in normal procedures and techniques. Size, orientation, location, and distribution require special considerations. This paper outlines how a high-sensitivity, immersion, ultrasonic technique is utilized to inspect a group of gear component and miscellaneous forgings suspected of having internal hydrogen flakes. The technique is successful in locating the discontinuities and distinguishing between the flakes and other types of discontinuities, specifically nonmetallic inclusions.