Figure 3-12. Using a Central Conductor to Circularly Magnetize Ring-Like Parts

Figure 3-9. Magnetic Field in Part used as a Conductor

Figure 3-14b. Longitudinal Field produced by the Coil Generates an Indication of Crack in Part

TM-1-1500-335-23 Nondestructive Inspection Methods Manual
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T.O. 33B-1-1 3-8 Figure 3-12. Using a Central Conductor to Circularly Magnetize Ring-Like Parts. 3.1.6.7 Longitudinal Magnetization. Electric current can also be used to create a longitudinal magnetic field in a test part with a current carrying encircling coil. Application of the right hand rule to any segment of a coiled conductor will show that the field within the coil consists of contributions from each turn of the coil and is aligned lengthwise as indicated as shown in Figure 3-13. Figure 3-13. Magnetic Lines of Force (Magnetic Field) in a Coil. 3.1.6.7.1 In Figure 3-14a. If a part is placed inside a coil; the magnetic lines of force created by the coil are aligned along the longitudinal axis of the coil. If the part is ferromagnetic, the high permeability concentrates the lines of flux within the part and induces a strong longitudinal magnetic field. 3.1.6.7.2 Longitudinal Magnetization with Inspection Equipment. Inspection of a cylindrical part using longitudinal magnetization is shown in Figure 3-14b. When a transverse discontinuity exists in the part, as in the illustration, a magnetic leakage field is formed at the crack location. This attracts magnetic particles, forming an MPI indication of the transverse discontinuity. Compare Figure 3-14b with Figure 3-10, and note that in both cases, a magnetic field has been induced in the part that is at right angles to the defect. This is the most desirable condition for reliable inspection. Figure 3-14a. Longitudinal Magnetic Field Produced in a Part Placed in a Coil.

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