Quantitative Inspection of Small Size Cracks by TOFD Based on Autoregressive Spectral Extrapolation

When time of flight diffraction (TOFD) is applied to detect small size crack in alloy steel weld, the diffraction waves at upper and lower points of crack will overlap and cause difficulty in quantifying the crack height due to restriction in the pulse width. In this paper, autoregressive spectrum extrapolation (ARSE) technique was applied to deal with the overlapped signals and extend effective band range to compress time domain pulse width and improve time resolution. The results showed that ARSE technique could effectively separate overlapped signals. Focusing on 100 mm thickness alloy steel of having a crack of 1.0 mm in height and 50 mm in depth, the quantitative error of crack height was no more than 5.3%.