Radiography, Eddy Current and ACFM
Five videos on the NDT methods CSWIP 3.1u and 3.2u expect you to recognise even if you never run them. I did not make them. I picked them, put them in teaching order, and wrote under each one what the exam wants you to take from it.
Video by video, with the exam angle
Each video teaches the concept. The line under it tells you how that concept turns up in the exam and where divers lose the mark.
Radiography: seeing inside the weld
Exam angle. X-rays or gamma rays go through the weld onto film. Solid steel soaks up radiation. A pore is a void, so more gets through and it shows dark on the film. That is why radiography is the method for internal porosity and slag, which no surface method can see.
Exam angle. Two things the exam asks every time. It gives a permanent record you can archive and compare. And it uses ionising radiation, so it needs a cleared exclusion zone and a certified radiographer. It is the most safety-critical method offshore.
Eddy current: surface flaws in conductive metal
Exam angle. An AC coil sets up a swirl of current in the metal under it. A crack breaks the swirl and the coil signal jumps. It needs a conductor, not a magnet, so it works on non-ferrous metals where MPI cannot. Surface and near-surface only, because the swirl fades fast with depth.
ACFM: find and size through paint
Exam angle. ACFM lays a smooth AC field in the steel surface. A crack forces the current around its ends and the probe reads the detour. Bigger detour, deeper and longer crack. It works through paint, so almost no cleaning. That is why it often beats MPI at weld toes offshore.
Exam angle. Watch it find and size in one pass. That is the exam point. MPI, eddy current and close visual are search tools. ACPD is a sizing tool. ACFM does both. Search first to find the crack, then size it, because depth decides how serious it is.
The course is the exam practice
These videos explain the methods. The NDTPrep 3.1u Interactive Theory course puts them in the order the syllabus uses, with the diagrams, the plain-English explanations, and a quiz at the end of every module. Then the Q&A and Flashcards drill it until it sticks.
The videos on this page belong to their creators. I have not edited them. My notes are my own reading of the CSWIP syllabus and are not endorsed by the video makers.