Data interpretation in ACPD crack inspection

Abstract

The voltages measured in the ACPD crack-sizing technique are sharply peaked at the crack edge for a short crack in a material of small skin depth, or for any crack in a material of large skin depth. The conventional sizing method uses these voltages as a first estimate of crack depth. A number of situations arise where these voltages may not be measured accurately, however, including rapid automated scanning and hand-held readings at weld toes. In such cases, more accurate sizing may be obtained using methods based on the saddle voltage with the probe straddling the crack. Multipliers have been calculated which allow crack depths to be estimated from the saddle voltage for circular arc or semi-elliptical cracks in the extremes of either small or large skin depth. These multipliers are presented in graphical form together with guidelines for their use.