TWI explains that TOFD was originally developed in the UK nuclear sector during the 1970s and has become widely recognized for its ability to size the height of embedded planar flaws. Its engineering value lies not in replacing every ultrasonic technique, but in providing stronger flaw-height assessment for defects such as cracks and lack of fusion.
Evident’s application material shows that TOFD is particularly useful for weld-root corrosion, erosion and heat-affected-zone metal loss where geometry is irregular and conventional pulse-echo methods can become difficult to interpret. For pressure piping, this makes TOFD a strong option for screening and quantitative assessment of long welds where a recorded scan is desirable.
At the same time, both TWI and Evident indicate that TOFD often works best as part of a combined inspection approach. Pulse-echo or phased array techniques are often needed to complement root, cap and position information. In practice, TOFD should therefore be selected as part of a coordinated inspection strategy based on thickness, weld geometry, access and code requirements.