FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 5. Nondestructive Inspection (NDI) | 3. Eddy Current Inspection | 5-30. Corrosion Inspection
9/8/98
AC 43.13-1B
(3) A reference standard is required for
the calibration of Eddy Current test equipment.
A reference standard is made from the same
material as that which is to be tested. A refer-
ence standard contains known flaws or cracks
and could include items such as: a flat surface
notch, a fastener head, a fastener hole, or a
countersink hole.
before performing the eddy current corrosion
inspection. The following are typical eddy
current equipment requirements for corrosion
inspection.
a. Use a variable frequency instrument
with frequency capability from 100 Hz to
40 kHz.
5-29. SUBSURFACE INSPECTION.
Eddy current inspection techniques are used to
inspect for subsurface cracks such as those
shown in figure 5-7. The following are typical
eddy current equipment requirements for sub-
surface crack inspections.
a. Use a variable frequency instrument
with frequency capability from 100 Hz to
500 MHz.
b. The probe used would be a low-
frequency; spot, ring, or sliding probe.
c. Use a reference standard appropriate
for the inspection being performed.
5-30. CORROSION INSPECTION.
Eddy current inspection is used to detect the
loss of metal as a result of corrosion. An esti-
mation of material loss due to corrosion can be
made by comparison with thickness standards.
Figure 5-8 shows typical structural corrosion
that may be detected by the use of eddy current
inspection. Remove all surface corrosion
b. Use a shielded probe with coil diame-
ter between 0.15 and 0.5 inch and designed to
operate at the lower frequencies.
c. A reference standard made from the
same alloy, heat treatment, and thickness as
the test structure will be required.
5-31. ESTABLISHING EDDY CURRENT
INSPECTION PROCEDURES. When es-
tablishing eddy current inspection procedures,
where no written procedures are available, the
following factors must be considered: type of
material to be inspected; accessibility of the
inspection area; material or part geometry, the
signal-to-noise ratio, test system; lift-off ef-
fects, location and size of flaws to be detected;
scanning pattern; scanning speed; and refer-
ence standards. All of these factors are inter-
related. Therefore, a change in one of the fac-
tors may require changes in other factors to
maintain the same level of sensitivity and reli-
ability of the eddy current inspection proce-
dure. Written procedures should elaborate on
these factors and place them in their proper or-
der.
Par 5-28
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