reading this section you will be able to do
what an immersion ultrasonic test is and why they are needed
way to couple the sound from transducer to a test object is coupling
the sound with water. This can be done with squirters where the
sound travels through a jet of water or by immersing the transducer
and test object in a tank of water. Both techniques are called
immersion testing. In immersion testing, the transducer
is placed in the water, above the test object, and a beam of sound
The graph of peaks using the immersion
method is slightly different. Between the initial pulse and the
back wall peaks there will be an additional peak caused by the
sound wave going from the water to the test material. This additional
peak is called the front wall peak. The ultrasonic tester can
be adjusted to ignore the initial pulse peak, so the first peak
it will show is the front wall peak. Some energy is lost when
the waves hit the test material, so the front wall peak is slightly
lower than the peak of the initial pulse.
Ultrasonic testing is an NDT test
technique that interrogates components and structures to detect
internal and surface breaking defects, and measures wall thickness
on hard (typically metallic or ceramic) components and structures.
ultrasonic testing work?
Ultrasonic operates on the principle
of injecting a very short pulse of ultrasound (typically between
0.1 MHz and 100 Mhz) into a component or structure, and then receiving
and analyzing any reflected sound pulses.
Conventionally, an operator scans
a transducer over the surface of the component in such a way that
he inspects all the area that is required to be tested by means
of a scanning motion. The inspection relies on the training and
integrity of the operator to ensure that he has inspected all
that is necessary.
Sound pulses reflected from features
within the component or structure are conventionally displayed
on a screen. The operator also has to interpret these signals
and report if the component or structure is defective or acceptable
according to the test specification that he is given.
Typical detection limits for fine
grained steel structures or components (hand scanning) are single
millimeter sized defects. Smaller defects can be detected by immersion
testing and a programmed scan pattern with higher frequency ultrasound
(slower testing). Detection limits are in the order of 0.1 to
0.2 mm, although smaller defects (typically 0.04mm diameter) can
be detected under laboratory conditions.
testing is completed with squirters where the sound travels
through a jet of water or by taking the transducer and test
object and immersing them in a tank of water.