9: Non-destructive Examination

The pattern formed by the particles will represent the shape and size of any
existing discontinuities as seen in Figure 23. The particles used during
the exam can be either dry or wet. If the examination is performed in normal
lighting the color of the particles should provide adequate contrast with the
exam surface.
The best results are achieved when the lines of flux are perpendicular to the
discontinuity. Typically, two inspections are performed,
one parallel to the weld and one across the weld to provide the maximum
coverage. When a magnetic force is applied to the material, a magnetic flux
field is created around and through the material. Discontinuities that are
perpendicular to the lines of flux will attract the magnetic particles causing an
indication as shown in Figure 24. Figure 25 illustrates the setup for detecting
transverse indications. The yoke is placed parallel on the weld to detect
discontinuities transverse to the weld. Figure 26 shows the setup for detecting
indications that run parallel to the weld. In this case, the yolk is placed across
the weld to detect discontinuities parallel to the weld.