In the same way, the shaft surface can be scanned for surface defects. In contrast to dye penetrant testing, cracks not open to the surface can be detected. Scheme of leaky Rayleigh wave testing of the valve seat. Test result obtained on a valve. The surface defects appear as nearly vertical lines.
Examples are the transition region and the notch area.
A first technique, which is used to inspect the valve head region, is digital radiography. The raw image is evaluated by digital image processing. A typical image resolution is 512 x 512 pixels with a pitch of 10 m. By subtraction and edge enhancement algorithms small defects are emphasized. In Fig. 4, an image with defects of 200 m size in the head region of the test valves mentioned above is shown.