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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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