The effect of probe oscillation (skew) on reflected signal amplitudes

Surprisingly, the effect of ultrasonic probe orientation on defect signal amplitudes has not been studied in detail in the open literature. This has significance for defect detection as the switch from manual to automated ultrasonics continues. This work measured the signal amplitudes from dozens of artificial defects to determine oscillation (also called skew) amplitude changes. As expected, the amplitudes dropped significantly, such that oscillations of 10 or more could easily result in missed defects. This result has significant importance for manual inspections, where operators are mandated to swivel probes. Oscillation effects, and the uncertainty of swivelling in service, could partly explain lower manual detection of defects.