Electromagnetic Testing Chapter 3- Electromagnetic Testing

The application of eddy current sensing elements is dependent on the
geometry of the part to be inspected. In cases where ferromagnetic parts are
to be inspected, large encircling coils or magnetic yokes may be incorporated
to magnetically saturate the test surface. The type, depth, location, and
orientation of the discontinuity are other important factors that affect probe
selection. Large encircling coils would hardly be suitable for detecting small
imperfections that can be readily detected with magnetic particle or
smalldiameter, surface-mount differential coils. An outer surface inspection of
a tube might not even be employed if the majority of defects encountered
were on the inside surface of the tube. In this case, inspection with an annular
probe might be all that is required.
Charlie Chong/ Fion Zhang