Electromagnetic Testing Chapter 3- Electromagnetic Testing

Defect location is a very important consideration. Internal defects in thick
parts may not be detected because the magnetic lines of flux will merely
bypass the defect on both sides and produce little or no leakage flux. Tubular
defects on the outer surface are easily detected by surface-mount probes
scanning the outer surface and inside surface defects are more easily
detected with surface mount probes scanning the inner surface.
Defects oriented so that they are normal or perpendicular to the surface and
normal or at right angles to the magnetic lines of flux will be more easily
detected than defects lying at an angle with respect to the surface or
magnetic lines of flux. Defects lying at shallow angles with regard to the
surface and oriented so that they are parallel to the magnetic lines of flux
produce the weakest lines of flux and will be difficult, if not impossible, to
detect.
Charlie Chong/ Fion Zhang