ToFD - time of flight diffraction

Time-of-flight diffraction (TOFD) method of ultrasonic testing is a sensitiveandaccurate method for thenondestructive testing of welds for defects. TOFD originated from tip diffraction techniques which were first published by Silk and Liddington[1] in 1975 which paved the way for TOFD. Later works on this technique are given in a number of sources which include Harumi et al. (1989), Avioli et al. (1991), and Bray and Stanley (1997).

Bray and Stanley (1997) summarized TOFD as tip-diffraction techniques which utilized the principle that the tips of a crack when struck by a wave will diffract the signals back to the other location on the surface. The depth of these tips can be determined from the diffracted energy.[2]

TOFD was invented in the UK in the 1970s initially as a research tool.[3] The use of TOFD enabled crack sizes to be measured more accurately, so that expensive  components could be kept in operation as long as possible with minimal risk of 


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