Figure 3-27. Stationary Wet Magnetic Particle Inspection Unit
Mobile inspection units are available in several sizes ranging from 2000 to 6000 amperes of AC and half-wave DC
outputs. The units have remote current output, ON/OFF and MAG/DEMAG controls that permit one-man operation at
the site of inspection. The units are used with either rigid or cable-wrapped coils for longitudinal magnetization and
demagnetization. Cables connected to a part or passing through it is used for circular magnetization or
demagnetization. Mobile units can be easily moved to any inspection site where suitable line input voltages and current
capacity are available.
Prods SHALL not be used to inspect aerospace components.
Both half-wave DC and AC outputs are included in most mobile and portable units to increase their versatility. Half-
wave DC current and dry magnetic powder make the best combination for detecting subsurface flaws in welds,
particularly when used with the prod method of inspection. Half-wave DC is also useful for detecting subsurface
discontinuities when the wet method is used. The use of alternating current is limited to the detection of discontinuities
that are open to the surface, such as cracks, and for demagnetizing parts.
A small portable unit that can be hand-carried is shown in Figure 3-28. These units have both AC and half-wave DC
outputs and must be used with portable or cable-wrapped coils for longitudinal magnetization. The units usually have a
remote ON/OFF control permitting a one-man operation. They can be used wherever an adequate 115-volt AC power