Time of Flight Diffraction (TOFD) method of ultrasonic testing, is a sensitive and accurate method for non-destructive testing of welds for defects. TOFD originated from tip diffraction techniques which were first published in 1975 paving the way for TOFD. TOFD was summarized 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. TOFD was invented in the UK in he 1970’s initially as a research tool. 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 failure.