[arsal]

It was explained a situation where TOFD is not ideal:
“In a situation where a high-low (poor fitup or mismatch) exists between two welded pieces, the transmitted pulse forms two signals off the opposite wall, one from the
higher side arriving prior to the one from the lower. The amount of high-low can be accurately assessed but if a defect occurred in the lower of the two sides the backwall
signal from the higher side could obscure the defect.
In both cases a pulse-echo technique can be adapted to
inspect these areas to provide improved coverage where TOFD is not ideal”.