INTRODUCTION
TO ULTRASONICS TESTING (UT)
Introduction to Ultrasonics
Basic Applications of Ultrasonics
Objective of Ultrasonics Testing
Training & Certification
Introduction to UT
Use of sound as a means of testing is known to man since
long. Audible sounds are generated when the breath of air
through the vocal chords that get excited and perform mechanical
oscillations. These oscillations are transferred through
the air in the form of pressure fluctuations that on falling
on the ear drum set it in motion. This perceive as audible
sound. We are aware that the sound waves are reflected when
they fall upon an obstacle which partly reflects and partly
transmits the energy. The audible sound waves lie in the
frequency range of 20 - 20000 Hz.
Frequencies above 20 kHz cannot be heard by man and sound
waves in these frequencies are called ultrasonic waves.
Ultrasonic waves are generated by some animals like dolphin,
bats they are also generated by mechanical means for example
during grinding of metals.
Early work of generation and application of ultrasonic
waves follow the discovery the piezoelectric effect in 1880.
Sokolov patented a through transmission technique in 1929
for assessment material condition. However the pulse echo
technique, which is widely applied today, gathered momentum
after the second world war.
Basic Application of Ultrasonics
Ultrasonic testing is a versatile inspection technique,
it is used to test a variety of both metallic & non-metallic
products, such as, welds, forgings, castings, sheet, tubing,
plastics & ceramics.
Ultrasonic testing has an advantage of detecting subsurface
discontinuities, with access to only one side of the specimen.
Objective of UT
1. Obtaining information related to discontinuities.
2. Disclosing the nature of the discontinuities without
impairing usefulness of product.
3. Separating acceptable and unacceptable materials in accordance
with predetermined standards.
Training & Certification
It is recognised that the effectiveness of nondestructive
testing depends on the capabilities of the personnel who
are responsible for, and perform NDT. Thus all customers
will require an assurance that NDT personnel whose specific
jobs require appropriate knowledge of the technical principles
underlying the nondestructive tests they perform, witness,
monitor, or evaluate be qualified and certified. In addition
every country may also have a program of training &
certifying personnel responsible for performing radiography
be qualified & certifies in safety aspects related use
of radiation sources.
The American Society for Nondestructive Testing recommends
the use of the documents “recommended practice no.
SNT-TC-1A”. This document provides
the employer with the necessary guidelines to properly qualify
and certify the NDT technician in all methods. To comply
with this document the employer must establish a “written
practice” which describes in detail how the technician
will be trained, examined and certified.
Current edition of SNT-TC-1A may be referred
to determine the recommended number of hours of classroom
instruction and months of experience necessary to be certified
as a radiographic testing technician. Certification of NDT
personnel always rests with the employer and is usually
at three levels.
Level I - is qualified to perform specific
calibrations, specific tests, and specific evaluations.
Level II - is qualified to set up and
calibrate equipment and to interpret and evaluate results
with respect to codes, standards and specifications. Must
be able to prepare written instructions and report test
results.
Level III - must be capable and responsible
for establishing techniques, interpreting codes, and designating
the test methods and techniques to be used . Must have a
practical background in the technology and be familiar with
other commonly used methods of NDT.
The SNT-TC-1A document recommends that
level I and level II NDT technicians be examined in the
following areas:
A. General examination.
B. Specific examination.
C. Practical examination.
The SNT-TC-1A document recommends that
NDT level III personnel be examined in the following areas:
A. Basic examination.
B. Method examination.
C. Specific examination.
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