Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

5.2.1.4 Flaw signals from absolute probes
At f 90 , the signals obtained using an absolute probe from a tube with a shallow
inside surface flaw, a shallow outside surface flaw, and a through hole appear
as shown in FIG. 5.33 when the display is rotated so that the orientation is
similar to that obtained from the same conditions during surface testing. Note
that a signal from decreasing fill factor is not normally obtainable. Instead, for
tube testing, the phase control is adjusted so that the signal from a shallow
inside surface flaw is approximately horizontal. Note that the illustration of
absolute probe signals in the ASME code is rotated 180° and is therefore upside
down with respect to FIG. 5.33. However the Code states that signals may be
rotated to the upper quadrants at the convenience of the operator. Since it is
standard practice internationally when performing surface testing to adjust the
phase to give the signal orientation shown in FIG. 5.33, it is strongly
recommended that the same orientation be used during tube testing to avoid
possible confusion.
Note: need further reading on ASME code
related subject matters
Charlie Chong/ Fion Zhang