Ultrasonic Computed Tomography − Pushing the Boundaries of the Ultrasonic Inspection of Forgings

Forgings, being usually one of the most critical components especially in power generation machinery, require intensive volumetric inspection to guarantee a sufficient lifetime. This is usually accomplished by manual or automated ultrasonic testing. The authors are reporting about a game changer in ultrasonic testing: Ultrasonic Computed Tomography uses analytics (i.e., a mathematical algorithm) to reconstruct the volume (In fact it uses a linearized diffraction tomographic approach for the solution of the inverse problem). This does not only allow to display indications spatially and visually correct in the 3D volume, but also improves the signal to noise ratio significantly, allowing an increase of sensitivity by up to an order of magnitude. The method is based on the Synthetic Aperture Focusing Technique (SAFT). The applied software is a brand-new implementation of SAFT with a strong focus for a large scale industrial application: the complete 2D as well as 3D reconstruction of ultrasonic inspections of heavy rotor forgings. This paper shows the working principle of the method along with the first results and computation times. Ultrasonic Computed Tomography is also awarded by the Werner von Siemens Award as one of the Top 15 ingenuity programs.