Time Of Flight Diffraction (TOFD)


The Time Of Flight Diffraction (TOFD) is a conventional NDT method.

The TOFD method typically uses a pair of conventional probes located on each side of a zone of interest (weld) (see pictures below). The probes are mounted on a scanning device that maintain a constant distance between the two probes.

TOFD inspection uses the “lateral wave echo” directly traveling from one probe to the user as reference for the surface, and the back-wall echo, indirectly traveling from one probe to the other via reflection off the back-wall, as reference for the back-wall.

On a “defect free” specimen, no indications above a selected threshold should be present in between these two echoes. On a “flawed” specimen, the TOFD inspection should show indications in between the lateral wave and the back-wall echoes. When a crack is present, there is a diffraction of the ultrasonic wave from the tips of the crack. Using the measured time-of-flight of the pulse, the depth of a crack tips can be calculated automatically by simple trigonometry.

TOFD_technique

TOFD

 

TOFD IMAGING

illustration TOFD

 

 

 

OUT OF INDICATION

Out of indication


TOFD Out of indication

 

THROUGH WALL NOTCH

Through wall notch

 

TOFD Through wall notch

 

 

 

USE OF TOFD IN FLAW DETECTOR GEKKO

gekko-3-4_2PA+TOFD-SOFTWARE

 

 

 

2PA+TOFD

GEKKO software showing the combination of two phased-arrays and TOFD