Resolution enhancement of ultrasonic defect signals for crack sizing

A practical algorithm has been developed to increase the time resolution of an ultrasonic system for inspecting pipeline girth welds via deconvolution with autoregressive spectral extrapolation. The full-width-half-maximum of the analytic signal magnitude of experimental echo pulses was reduced by an average of 80% by this technique. There is also a reduction in the size of the dead zone at the weld root by close to 80%, in addition to a corresponding decrease in uncertainty of sizing estimates of cracks through crack-tip diffraction methods. The algorithm is used to inspect a test plate containing manufactured flaws with nominal depths ranging from 0.5 mm to 5 mm. Calculated values of crack depth were found to be consistent with destructive measurements of crack profiles.

► Autoregressive spectral extrapolation sharpened ultrasonic echo resolution.
► Uncertainty in ultrasonic echo timing has been reduced by 80%.
► Major improvements in TOFD crack sizing by using spectral extrapolation.
► Dead zone for defect detection at weld root reduced by 75%.