ULTRASONIC TESTING

INTRODUCTION:

• This module presents an introduction to the NDT method of ultrasonic testing.
• Ultrasonic testing uses high frequency sound energy to conduct examinations and make measurements.
• Ultrasonic examinations can be conducted on a wide variety of material forms including castings, forgings, welds, and composites.

A considerable amount of information about the part being examined can be collected, such as the presence of discontinuities, part or coating thickness; and acoustical properties can often be correlated to certain properties of the material

OUTLINE FOR ULTRASONIC TESTING :

• Basic Principles of sound generation
• Transducers
• Instrumentation
• Advantages and Limitations

BASIC PRINCIPLES OF SOUND:

• Sound is produced by a vibrating body and travels in the form of a wave.
• Sound waves travel through materials by vibrating the particles that make up the material.
• The pitch of the sound is determined by the  frequency of the wave  (vibrations or cycles  completed in a certain
  period of time).
• Ultrasound is sound with a pitch too high to be detected by the human ear.

ULTRASONIC GENERATION IN ULTRASONIC TESTING:

              Ultrasound is generated with a transducer in ultrasonic testing.

PRINCIPLES OF ULTRASONIC GENERATIION:

• Ultrasonic waves are introduced into a material where they travel in a straight line and at a constant speed until they encounter a surface.
• At surface interfaces some of the wave energy is reflected and some is transmitted.
• The amount of reflected or transmitted energy can be detected and provides information about the size of the reflector.

TRANSDUCERS IN ULTRASONIC TESTING:

• Transducers are manufactured in a variety of forms, shapes and sizes for varying applications.

Transducer

INSTRUMENTATION IN ULTRASONIC TESTING:

• In Ultrasonic testing, Ultrasonic equipment is usually purchased to satisfy specific inspection needs, some users may purchase general purpose equipment to fulfill a number of inspection applications.

Instrument

ADVANTAGES OF ULTRASONIC TESTING:

• Ultrasonic testing is sensitive to small discontinuities both surface and subsurface.
• Depth of penetration for flaw detection or measurement is superior to other methods.
• Only single-sided access is needed when pulse-echo technique is used.
• Ultrasonic testing has high accuracy in determining reflector position and estimating size and shape.
• Minimal part preparation required.
• In Ultrasonic testing, Electronic equipment provides instantaneous results.
• Detailed images can be produced with automated systems.
• Has other uses such as thickness measurements, in addition to flaw detection.

LIMITATIONS OF ULTRASONIC TESTING:

• In Ultrasonic testing, surface must be accessible to transmit ultrasound.
• Skill and training is more extensive than with some other methods.
• Ultrasonic testing normally requires a coupling medium to promote transfer of sound energy into test specimen.
• Materials that are rough, irregular in shape, very small, exceptionally thin or not homogeneous are difficult to inspect.
• Cast iron and other coarse grained materials are difficult to inspect in ultrasonic testing  due to low sound transmission and high signal noise.
• Linear defects oriented parallel to the sound beam may go undetected.
• Reference standards are required for both equipment calibration, and characterization of flaws in Ultrasonic testing.

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