Crack Measurement in Steel Plates Using TOFD Method

Abstract

In this study, the ultrasonic time of flight diffraction (TOFD) method to locate and size flaws in steel members was evaluated. This was done by measuring the location and depth of flaws implanted in steel plate specimens and of a fatigue crack in the flange of a full-scale steel plate girder. The data showed that the TOFD procedure was very accurate to locate flaws (within 5% of the actual location). The accuracy of the procedure to measure flaw depth depends, however, on the proximity of the flaw tip to the scanning surface. Flaw tips at depths ≥6 mm below the scanning surface were measured to an accuracy of 20% of the actual value. When the flaw tip was at a depth ≤3 mm below the scanning surface, flaw depth was overestimated. Additional scans on the opposite surface of the material may be used, however, to overcome this limitation and to obtain an accurate measurement of such flaws. The method offered good repeatability and can be used to accurately locate and size flaws with an appropriate scanning scheme.