Ultrasonic

Introduction to Ultrasonic Testing

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Introduction to
Ultrasonic Testing

Basic Principles of Ultrasonic Testing
Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make
measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional
measurements, materialcharacterization, and more. To illustrate the general inspection principle, a
typical pulse/echo inspection configuration as illustrated below will be used.
A typical UT inspection system consists of several functional units, such as the pulser/receiver,
transducer, and display devices. A pulser/receiver is an electronic device that can produce high
voltage electrical pulse. Driven by the pulser, thetransducer generates high frequency ultrasonic
energy. The sound energy is introduced and propagates through the materials in the form of waves.
When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected
back from the flaw surface. The reflected wave signal is transformed into electrical signal by the
transducer and is displayed on a screen. In theapplet below, the reflected signal strength is displayed
versus the time from signal generation to when a echo was received. Signal travel time can be
directly related to the distance that the signal traveled. From the signal, information about the
reflector location, size, orientation and other features can sometimes be gained.

Introduction
Basic Principles
History
Present State
FutureDirection
Physics of Ultrasound
Wave Propagation
Modes of Sound Waves
Properties of Plane Waves
Wavelength/Flaw Detection
Elastic Properties of Solids
Attenuation
Acoustic Impedance
Reflection/Transmission
Refraction & Snell's Law
Mode Conversion
Signal-to-noise Ratio
Wave Interference
Equipment &
Transducers
Piezoelectric Transducers
Characteristics of PT
Radiated FieldsTransducers Beam Spread
Transducer Types
Transducer Testing I
Transducer Testing II
Transducer Modeling
Couplant
EMATs
Pulser-Receivers
Tone Burst Generators
Function Generators
Impedance Matching
Data Presentation
Error Analysis
Measurement
Techniques
Normal Beam Inspection
Angle Beams I
Angle Beams II
Crack Tip Diffraction
Automated Scanning
Velocity Measurements
Measuring AttenuationUltrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of
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Introduction to Ultrasonic Testing

ultrasonic inspection that are often cited include:
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It is sensitive to both surface and subsurfacediscontinuities.
The depth of penetration for flaw detection or measurement is superior to other NDT methods.
Only single-sided access is needed when the pulse-echo technique is used.
It is high accuracy in determining reflector position and estimating size and shape.
Minimal part preparation required.
Electronic equipment provides instantaneous results.
Detailed images can be produced with automatedsystems.
It has other uses such as thickness measurements, in addition to flaw detection.

As with all NDT methods, ultrasonic inspection also has its limitations, which include:
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Surface must be accessible to transmit ultrasound.
Skill and training is more extensive than with some other methods.
It normally requires a coupling medium to promote transfer of soundenergy 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 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...