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Please note this is a free NDT training UT
ultrasound class review for a non-technical look at the ultrasonic
NDT method in reference to nondestructive testing. Some terms in
this article might not be industry appropriate and other things are
simply skipped. For an ultrasound course per SNT-TC-1A or NAS-410
or CP-189 contact a training facility and schedule your NDT
training, something we can easily accomplish for you. (shameless
plug). UT is commonly used on composites, metals and plastics in
the aerospace, nuclear, and industrial industries.
Ultrasound (UT) is also called ultrasonics, UT
straight beam (longitudinal), UT shear wave, UT immersion testing,
UT phased array and UTT for ultrasonic thickness. They are all
essentially ultrasound, but in the NDT industry UTT, straight beam
and shear wave are quick ways to define the type of inspector you
are. When determining an inspector’s certification level, a UT
shear wave weld inspector usually represents a well-versed
technician in the art of ultrasonics. Longitudinal inspector is
someone familiar with ultrasonics, but uses it for sending sound on
a straight path and usually does not have much experience with the
interaction of sound reflecting within metals or materials being
inspected. A UTT inspector has usually undergone minimal training
and is certified to utilize direct readout instrumentation for the
thickness determination of metals. A good longitudinal or thickness
technician does not constitute a shear wave inspector.
So what is NDT UT ultrasound testing? The
text book answer is sound over what human hearing is capable of
detecting, which is 20,000 HZ. For some this answer is too easy
and to others it is quite complicated. Let’s start with the
basics of a car stereo played very loud with very large speakers
driving through your neighborhood at night. When you hear the car
approaching you usually do not hear the voices of the music
playing, you hear the deep base and perhaps the car muffler.
These frequencies are very low in the 50 Hz range. You ask
yourself how can that person stand that music, he is probably
going to go deaf? You say this to yourself because you feel the
vibrations from the speakers even inside of your house. There is
no hesitation from you when asked if sound can move things,
because it is moving your windows .
When utilizing an
ultrasonic machine you can put your ear up to the ultrasonic
transducer (ultrasound speaker and microphone) and you will not hear
a thing,
you place the transducer on your finger and you will feel nothing. But
within a part or metal the sound is displacing and vibrating things,
you just cannot see it or feel it. That is how an ultrasonic
cleaner at a jewelry store works. The fluid in the tank allows the
sound to travel efficiently and the ultrasound cleans the jewelry.
The next conversation of UT ultrasound that you
would normally receive in a class is the dropping a stone in a lake
speech. This is a great
way to create a visual of motion and an acceptable visual
representation of sound transferring through the material.
This imagery makes it possible to understand how a calibrated ultrasonic instrument could measure each
sound wave or ripple. That is how the instrumentation
measures how far sound travels in a material. If you could
t put a
ruler to the ripples you would be able to measure how far apart they are
and how far they traveled. Another important part is to
realize that the ripples get disappear do to attenuation (absorption
of sound) by the body of water
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