TM 1-1520-253-23
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 55-1500-335-23 (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 degrees 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 should 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.
