Primarily for general aviation discussion, but other aviation topics are also welcome.
By markpodbery
#1912976
Quick question to any eddy current testers for this PA28 AD.

I was randomly reading about the general process and I know the AD was to do with the bolt holes does this apply or is it in general? I know they spin the device in the bolt holes but I think the below is to do with general eddy current testing on anything…

“A disadvantage of the testing what does this actually mean?

ECT current always runs parallel to the surface of a material, so a defect that doesn’t come in direct contact with the current can’t be detected—and this means that some defects may go undetected

Maybe irrelevant! Just interested.
User avatar
By lobstaboy
#1912980
Eddy currents flow through the surface of the metal under examination. Depending on the frequency they penetrate down to a short distance, known as the skin depth. The detection process relies on a defect getting in the way of these surface currents. Cracks will always appear at the surface, so are well detected by ECT. Fatigue, stress corrosion etc.
Where ECT is less good is for things like porosity in welds (bubbles frozen into the metal, basically) because they don't break the surface and hence don't interrupt the current. Not really so relevant in many aircraft structures.
Flyin'Dutch' liked this