Chapter 18 Weld Inspection and Repair
269
A fl uorescent penetrant test requires an ultra-
violet light (black light) to observe the test results. It
may be necessary to enclose the viewing area in order
to properly read the test results.
Magnetic Particle Test
A magnetic particle test (MT) is a nondestruc-
tive method of detecting cracks, seams, inclusions,
segregations, porosity, or lack of fusion in magnetic
materials. This test can detect surface defects that
are too fi ne to be seen with the naked eye or that lie
slightly below the surface.
When a magnetic fi eld is established in a ferro-
magnetic material, minute poles are set up at any
defects. These poles have a stronger attraction for
magnetic particles than the surrounding material has.
In a magnetic particle test, the ferromagnetic material
is magnetized by an electric current, and iron parti-
cles or powder is applied to the magnetized area. If
the magnetic fi eld is interrupted by a defect, the iron
particles form a pattern on the surface. The pattern is
the approximate size of the defect. Figure 18-6 shows
how magnetic particle tests are performed.
Small, portable, permanent magnets can be used
for thin-gauge materials. Heavier material requires
power from transformers, generators, or rectifi ers. A
typical magnetic particle unit is shown in Figure 18-7.
The magnetic particle test can be performed
using either the wet or the dry method, depending on
the individual application. The wet method, in which
the particles are suspended in a fl uid, is generally
more sensitive than the dry method. Wet magnetic
particle inspection allows for a more even distribution
of particles over a large area and is better for detecting
very small discontinuities on a smooth surface. The
dry method, which uses fi nely divided dry particles
that are dusted onto a magnetized surface, is better
for rough surfaces. Either red or gray particles can
be used in the test. The color selected should provide
good contrast with the material being tested.
A
B
Penetrant
Penetrant
Apply penetrant on the
inside of the vessel.
Apply developer on the
outside of the vessel.
Figure 18-5. Minute leaks in tanks or vessels can be
located using penetrant inspection. A—Dye penetrant
inspection of an open-top tank. B—Dye penetrant
inspection of a closed tank.
Yoke
Part
Weld
Magnetic lines
of force
Figure 18-6. Magnetic particle tests. One pole of the yoke
is placed on each side of the weld.
Figure 18-7. Magnetic particle units are very useful on
small weldments and require only 110 volts for operation.
(Magnafl ux, A Division of Illinois Tool Works)
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Chapter 18 Weld Inspection and Repair
269
A fl uorescent penetrant test requires an ultra-
violet light (black light) to observe the test results. It
may be necessary to enclose the viewing area in order
to properly read the test results.
Magnetic Particle Test
A magnetic particle test (MT) is a nondestruc-
tive method of detecting cracks, seams, inclusions,
segregations, porosity, or lack of fusion in magnetic
materials. This test can detect surface defects that
are too fi ne to be seen with the naked eye or that lie
slightly below the surface.
When a magnetic fi eld is established in a ferro-
magnetic material, minute poles are set up at any
defects. These poles have a stronger attraction for
magnetic particles than the surrounding material has.
In a magnetic particle test, the ferromagnetic material
is magnetized by an electric current, and iron parti-
cles or powder is applied to the magnetized area. If
the magnetic fi eld is interrupted by a defect, the iron
particles form a pattern on the surface. The pattern is
the approximate size of the defect. Figure 18-6 shows
how magnetic particle tests are performed.
Small, portable, permanent magnets can be used
for thin-gauge materials. Heavier material requires
power from transformers, generators, or rectifi ers. A
typical magnetic particle unit is shown in Figure 18-7.
The magnetic particle test can be performed
using either the wet or the dry method, depending on
the individual application. The wet method, in which
the particles are suspended in a fl uid, is generally
more sensitive than the dry method. Wet magnetic
particle inspection allows for a more even distribution
of particles over a large area and is better for detecting
very small discontinuities on a smooth surface. The
dry method, which uses fi nely divided dry particles
that are dusted onto a magnetized surface, is better
for rough surfaces. Either red or gray particles can
be used in the test. The color selected should provide
good contrast with the material being tested.
A
B
Penetrant
Penetrant
Apply penetrant on the
inside of the vessel.
Apply developer on the
outside of the vessel.
Figure 18-5. Minute leaks in tanks or vessels can be
located using penetrant inspection. A—Dye penetrant
inspection of an open-top tank. B—Dye penetrant
inspection of a closed tank.
Yoke
Part
Weld
Magnetic lines
of force
Figure 18-6. Magnetic particle tests. One pole of the yoke
is placed on each side of the weld.
Figure 18-7. Magnetic particle units are very useful on
small weldments and require only 110 volts for operation.
(Magnafl ux, A Division of Illinois Tool Works)

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