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Radiography
Radiography utilises very
short wavelength electromagnetic radiation, namely
X-rays or γ rays, will penetrate through solid media but
will be partially absorbed by the medium. The amount of
absorption which will occur will depend on the thickness
and density of the material the radiation is passing
through, and also the characteristics of the radiation
the radiation which passes through the material can be
detected and recorded on either film or sensitized
paper, viewed on a fluorescent screen or detected and
monitored by electronic sensing equipment.
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Ultrasonic
Testing
Ultrasonic testing is
widely used for the detection of internal defects in
materials, but they can also be used for the detection
of small surface cracks. Ultrasonic are used for the
quality control inspection of part processed material,
such as rolled slabs, as well as for the inspection of
finished components.
The waves used for the
non-destructive testing of material are usually within
the frequency range 0.5MHz to 20MHz.
In fluids, sound waves are
of the longitudinal compression type in which the
particle displacement is in the direction of
propagation; but in solids, they are shear waves, with
particle displacement is normal to the direction of wave
travel and elastic surface waves can also occur. The
latter are termed Rayleigh waves.
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Hardness
Testing
Per
ASTM E110, this testing is normally used for on-site
applications or on very large samples. The portable
hardness unit performs the hardness testing by applying
a 5 kg. Vickers load indenter and electronically
converts the values in the preferred scale.
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Magnetic
Particle Inspection
Magnetic particle
inspection is a sensitive method of locating surface and
some sub-surface defects in Ferro-magnetic components.
The basics processing parameters depend on relatively
simple concepts. In essence, when a ferromagnetic
component is magnetized, magnetic discontinuities that
lie in a direction approximately perpendicular to the
field direction will result in the formation of strong
‘leakage field’. This leakage field is present at and
above the surface of the component, and its presence is
visibly detected by the utilization of finely divided
magnetic particles. The application of dry or wet
particles in a liquid carrier, over the surface of the
component, results in a collection of magnetic particle
at a discontinuity.
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Liquid Penetrant Testing
Liquid penetrant testing is
a technique, which can be used to detect defects in a wide
range of components, provided that the defect breaks the
surface of the material. The principle of the technique is
that a liquid is drawn by capillary attraction in to the
developer, after subsequent development, any surface
breaking defects may be rendered visible to the human eye.
In order to achieve good defects visibility, the
penetrating liquid will either be coloured with a bright
and persistent dye or else contains a fluorescent
compound. In the former type the dye is generally red and
the developed surface can be viewed in natural or
artificial light, but in latter case the component must be
viewed under ultra-violet light if indication of defects
is to be seen.
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