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182 Part III: Inspection and Test
Part III.D.1
reactors. Video cameras and camcorders are also considered tools for visual
inspection.
Radiation. An X-ray machine or radioactive isotope is used as a source of radiation,
which is directed through the test part and onto a recording medium such as
film. When the film is developed, a radiograph is obtained that can show the internal
condition of a part (Aircrat NDT 2008). This radiation has higher energy and
a shorter wavelength than visible light, which gives it the ability to penetrate different
objects, showing cracks and other object defects (Larson 2000). Figure 17.2
shows the method of inspecting using X-ray.
The different shades on the film indicate different thicknesses, showing
defects existing in the object. Figure 17.3 shows an example of an object that is
being inspected by X-ray.
X-ray and radiation testing can adversely affect the health of the people performing
the tests. Appropriate precautions and policies have to be followed in
order to protect users. Radioactive waste should be taken into consideration for
environmental and biological reasons (NDT-ED 2008b).
Eddy Current. Eddy current is an electromagnetic nondestructive testing method
in which electric currents are generated in a conductive material by an induced,
varying magnetic field. Changes in the flow caused by variations in the object
are reflected into a nearby coil or coils where they are detected and measured by
suitable instrumentation (Aircraft NDT 2008). Figure 17.4 depicts the Eddy current
method. This type of testing can be used for detecting surface cracks but can
High electrical potential
Electrons
+ –
X-ray generator
Radiation
Radiation
penetrates the
sample
Exposure recording device (Film)
Figure 17.2 Inspection using X-ray.