The most common form of weld inspection subsea is Eddy Current using divers. This has always been effective if somewhat costly.
At HPRROV we pioneered the use of ACFM (Alternating Current Field Measurement) using a Falcon ROV system
As with any weld inspection, marine growth requires removal for a clear CVI and crack detection. (See our CaviBlaster page)
ACFM has proved itself in that it can detect a surface breaking weld and give depth penetration down to 25mm and beyond.
Mounted on the robotic arm of a Falcon ROV proved very dexterous and allowed readings to be taken through the 360 degrees of the tubular.