TM 1-1520-265-23
1-28 Change 2
1.4.8.1 Magnetic Particle Inspection Equipment. Considerations involved in the selection of
magnetic particle inspection equipment include the type of magnetizing current and the location and
nature of the inspection. The purpose of this manual is to support the accomplishment of NDI at the
AVUM and AVIM levels. This dictates equipment that can be used on or off the helicopter at remote
sites. Therefore, magnetic particle procedures in this manual use the electromagnetic yokes or
probes and hand-held coils as shown in Figure 1-6. This equipment is common and readily available
to AVUM and AVIM levels. Stationary magnetic particle equipment can be used if facilities, required
shop equipment, and qualified NDI technicians are available. Refer to TM 1-1500-335-23
(Nondestructive Inspection Methods manual) for stationary magnetic particle inspection
techniques.
1.4.8.1.1 Magnetic Yokes and Probes.. Portable induced field inspection equipment is generally
referred to as either a probe or a yoke. These terms are synonymous and differ due to
manufacturer’s nomenclature. They are small, portable, easy to use, and can be used on or off the
helicopter. They induce a strong magnetic field into that portion of a part that lies between the poles
or legs. This limits the magnetization to longitudinal; however, by turning the probe 90_ on the part
for the second position, cracks, either perpendicular or parallel to the axis of the part, can be
detected. Some yokes and probes have both AC and DC capabilities while others have AC only. All
procedures in this manual use AC. AC provides a very desirable and useful field. The vibratory action
of AC adds significantly to the magnetic particle mobility enhancing the formation and build-up of
larger and sharper indications at discontinuities. An AC magnetic field is also used when it is
necessary to reveal only surface cracks, common to in-service parts due to fatigue and stress
cracking. Yokes and probes utilizing AC for magnetization also have the additional advantage that
they can be used for demagnetization.
1.4.8.1.2 Hand-held Coil. For longitudinal magnetization of bolts, shafts, spindles, axles, and
similar small parts, the hand-held coil offers a simple, convenient method of inspecting for
transverse cracks. It allows for equipment maintenance inspections wherever a coil can be applied
around the part. Parts are magnetized and demagnetized with the same coil.
1.4.8.2 Safety Precautions During Magnetic Particle Inspections. Follow safety precautions and
instructions contained in this manual and the Nondestructive Inspection Methods manual listed in
Table 1-1.
WARNING
Black lights generate considerable heat during use. Extreme care must be
exercised to prevent contacting the housing with any part of the body.
To prevent injury to eyes, do not look directly into black light.
Prolonged direct exposure of hands to the filtered black light’s main beam may be
harmful. Suitable gloves shall be worn when exposing hands to the main beam.
a. Follow manufacturer’s instructions when using black lights and filter.
b. Do not wear sunglasses or glasses with light-sensitive lenses during fluorescent magnetic
particle inspections. They can contribute to improper interpretation of defects.
