Unit 4 ultrasonic testing method

Unit -4
Ultrasonic Testing
6/25/2021 SHIVAM SHARMA 1

ULTRASONIC TESTING

CONTENT
• Introduction
• Basic principles of sound generation
• Principles of ultrasonic inspection
• Test techniques
• Equipment
Transducers
Instrumentation
References of standards
• Advantage of ultrasonic Testing
• Limitation of ultrasonic Testing

What are ultrasound?
• Ultrasounds are acoustic waves with frequencies
greater than 20 kHz, which are too high to be
audible by humans.

What are ultrasonic wave?
•Ultrasonic waves are mechanic waves originated by the
vibration/oscillation of the elementary particles (atoms or
molecules) that constitutes the material (medium, more
generally)
• The propagation medium can be solid, liquid or gas
• In liquid and gas only longitudinal waves are possible to
propagate
• The ultrasonic waves do not propagate in the vacuum

Introduction
•Ultrasonic testing (UT) is a family of non-
destructive testing techniques based on
propagation of ultrasonic waves in the object
or the material tested.
•For Ultrasonic testing application very short
pulse of ultrasonic waves are transmitted
into materials to detect internal flaws or to
characterize the material.

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.

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.

Basic Principles of Sound (cont.)
• The measurement of sound waves from crest to crest
determines its wavelength (λ).
• The time is takes a sound wave to travel a distance of one
complete wavelength is the same amount of time it takes the
source to execute one complete vibration.
• The sound wavelength
is inversely proportional
to its frequency. (λ = 1/f)
• Several wave modes of
vibration are used in
ultrasonic inspection.
The most common are
longitudinal, shear, and
Rayleigh (surface) waves.

Basic Principles of Sound (cont.)
• Ultrasonic waves are very similar to light waves
in that they can be reflected, refracted, and
focused.
• Reflection and refraction occurs when sound
waves interact with interfaces of differing
acoustic properties.
• In solid materials, the vibrational energy can be
split into different wave modes when the wave
encounters an interface at an angle other than
90 degrees.
• Ultrasonic reflections from the presence of
discontinuities or geometric features enables
detection and location.
• The velocity of sound in a given material is
constant and can only be altered by a change in
the mode of energy.

Ultrasound Generation
The transducer is
capable of both
transmitting and
receiving sound
energy.
Ultrasound is generated with a transducer.
A piezoelectric element
in the transducer
converts electrical
energy into mechanical
vibrations (sound), and
vice versa.

Principles of Ultrasonic Inspection
• 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.
• The travel time of the sound can be measured and this
provides information on the distance that the sound has
traveled.

Test Techniques
• Ultrasonic testing is a very versatile inspection method, and
inspections can be accomplished in a number of different ways.
• Ultrasonic inspection techniques are commonly divided into
three primary classifications.
• Pulse-echo and Through Transmission
(Relates to whether reflected or transmitted energy is used)
• Normal Beam and Angle Beam
(Relates to the angle that the sound energy enters the test article)
• Contact and Immersion
(Relates to the method of coupling the transducer to the test article)
Each of these techniques will be discussed briefly
in the following slides.

• In pulse-echo testing, a transducer sends out a pulse of energy
and the same or a second transducer listens for reflected energy
(an echo).
• Reflections occur due to the presence of discontinuities and the
surfaces of the test article.
• The amount of reflected sound energy is displayed versus time,
which provides the inspector information about the size and the
location of features that reflect the sound.
f
Test Techniques - Pulse-Echo
plate
crack
0 2 4 6 8 10
initial
pulse
crack
echo
back surface
echo
UT Instrument Screen

Test Techniques – Pulse-Echo (cont.)
Digital display
showing signal
generated from
sound reflecting
off back surface.
Digital display
showing the presence
of a reflector midway
through material, with
lower amplitude back
surface reflector.
The pulse-echo technique allows testing when access to only one
side of the material is possible, and it allows the location of
reflectors to be precisely determined.

Test Techniques – Through-Transmission
0 2 4 6 8 10
2
1
1
• Two transducers located on
opposing sides of the test
specimen are used. One
transducer acts as a transmitter,
the other as a receiver.
• Discontinuities in the sound path
will result in a partial or total loss
of sound being transmitted and
be indicated by a decrease in the
received signal amplitude.
• Through transmission is useful in
detecting discontinuities that are
not good reflectors, and when
signal strength is weak. It does
not provide depth information.
T R
T R
1
1
2

Digital display
showing received
sound through
material
thickness.
Digital display
showing loss of
received signal
due to presence
of a discontinuity
in the sound field.
Test Techniques – Through-Transmission

Test Techniques – Normal and Angle Beam
• In normal beam testing, the sound
beam is introduced into the test
article at 90 degree to the surface.
• In angle beam testing, the sound
beam is introduced into the test
article at some angle other than
90.
• The choice between normal and
angle beam inspection usually
depends on two considerations:
- The orientation of the feature of
interest – the sound should be
directed to produce the largest
reflection from the feature.
- Obstructions on the surface of the
part that must be worked around.

0 2 4 6 8 10
FWE
BWE
DE
2
IP
IP = Initial Pulse
FWE = Front Wall
Echo
DE = Defect Echo
BWE = Back Wall
Echo
0 2 4 6 8 10
FWE
BWE
1
IP
1 2
Defect
Test Techniques – Contact Vs Immersion
• To get useful levels of sound energy into a material, the air
between the transducer and the test article must be removed.
This is referred to as coupling.
• In contact testing (shown on the previous slides) a couplant
such as water, oil or a gel is applied between the transducer
and the part.
• In immersion testing, the part and the transducer are place in a
water bath. This arrangement allows better movement of the
transducer while maintaining consistent coupling.
• With immersion testing, an echo from the front surface of the
part is seen in the signal but otherwise signal interpretation is
the same for the two techniques.

Piezoelectric Effect
• The conversion of electrical pulses to mechanical vibrations and
the conversion of returned mechanical vibrations back into
electrical energy is the basis for ultrasonic testing. This
conversion is done by the transducer using a piece of piezoelectric
material (a polarized material having some parts of the molecule
positively charged, while other parts of the molecule are
negatively charged) with electrodes attached to two of its opposite
faces. When an electric field is applied across the material, the
polarized molecules will align themselves with the electric field
causing the material to change dimensions. In addition, a
permanently-polarized material such as quartz (SiO2) or barium
titanate (BaTiO3) will produce an electric field when the material
changes dimensions as a result of an imposed mechanical force.
This phenomenon is known as the piezoelectric effect

EQUIPMENT FOR ULTRASONIC
APPLICATIONS
• 1. Transducer
• 2. Pulser (clock)
• 3. Receiver/amplifier
• 4. Display (screen)
1. The clock signals the pulser to provide a short, high-voltage pulse to the
transducer while simultaneously supplying a voltage to the time-base trigger
module.
2. The time-base trigger starts the “spot” in the CRT on its journey across the
screen.
3. The voltage pulse reaches the transducer and is converted into mechanical
vibrations (see “piezoelectricity”), which enter the test piece. These vibrations
(energy) now travel along their “sound path” through the test piece. All this
time, the spot is moving horizontally across the CRT.

4. The energy in the test piece now reflects off the interface (back
wall) back toward the transducer, where it is reconverted into a
voltage. (The reconverted voltage is a fraction of its original value.)
5. This voltage is now received and amplified by the
receiver/amplifier.
6. The amplified voltage is sent to the “vertical (Y axis) plates” (top
and bottom) in the CRT. At this time, the upper Y axis plate attracts
the spot upward. This motion produces the “signal” on the screen
that signifies the time that the energy has taken to make the round
trip through the test piece, from the moment the energy leaves the
transducer until it is received by the transducer. The spot is set to
start its trip at the time the energy enters the test piece. This is
manually adjusted by using the delay or zero control. This step is
particularly necessary when using a Plexiglas delay line (see
Glossary of Terms).

Conti…
7. The same “packet” of returning energy has by this time reflected
down off the test piece’s top interface and now makes a second trip
down through the test piece. (The spot continues its horizontal
journey across the screen.) The energy reflects once more off the
back wall interface and returns again to be received and amplified.
The

CRO techniques
• The cathode-ray oscilloscope (CRO) is a multipurpose display instrument
used for the observation, measurement , and analysis of waveforms by
plotting amplitude along y-axis and time along x-axis.
• CRO is generally an x-y plotter; on a single screen it can display
different signals applied to different channels. It can measure amplitude,
frequencies and phase shift of various signals. Many physical quantities
like temperature, pressure and strain can be converted into electrical
signals by the use of transducers, and the signals can be displayed on the
CRO.
• A moving luminous spot over the screen displays the signal. CROs are
used to study waveforms, and other time varying phenomena from very
low to very high frequencies.

The central unit of the oscilloscope is the cathoderay tube
(CRT), and the remaining part of the CRO consists of the
circuitry required to operate the cathode-ray tube.
The CRO consists of the following:
(i) CRT
(ii) Vertical amplifier
(iii) Delay line
(iv) Horizontal amplifier
(v) Time-base generator
(vi) Triggering circuit
(vii) Power supply

Inspection Applications
Some of the applications for which ultrasonic testing may be
employed include:
• Flaw detection (cracks, inclusions, porosity, etc.)
• Erosion & corrosion thickness gauging
• Assessment of bond integrity in adhesively
joined and brazed components
• Estimation of void content in composites and
plastics
• Measurement of case hardening depth in steels
• Estimation of grain size in metals
On the following slides are examples of some
common applications of ultrasonic inspection.

Thickness Gauging
• Ultrasonic thickness gauging is
routinely utilized in the
petrochemical and utility
industries to determine various
degrees of corrosion/erosion.
• Applications
include piping
systems, storage
and containment
facilities, and
pressure vessels.

Flaw Detection - Delaminations
Signal showing multiple back
surface echoes in an unflawed area.
Additional echoes indicate
delaminations in the member.
Contact, pulse-echo inspection for delaminations
on 36” rolled beam.

Flaw Detection in Welds
• One of the most widely used
methods of inspecting
weldments is ultrasonic
inspection.
• Full penetration groove
welds lend themselves
readily to angle beam shear
wave examination.

Equipment
Equipment for ultrasonic testing is very diversified. Proper selection
is important to insure accurate inspection data as desired for specific
applications.
In general, there are three basic components that comprise an
ultrasonic test system:
- Instrumentation
- Transducers
- Calibration Standards

Transducers
• Transducers are manufactured in a variety of
forms, shapes and sizes for varying applications.
• Transducers are categorized in a number of ways
which include:
- Contact or immersion
- Single or dual element
- Normal or angle beam
• In selecting a transducer
for a given application, it
is important to choose the
desired frequency,
bandwidth, size, and in some cases focusing
which optimizes the inspection capabilities.

Contact Transducers
Contact transducers are
designed to withstand
rigorous use, and usually
have a wear plate on the
bottom surface to protect the
piezoelectric element from
contact with the surface of
the test article.
Many incorporate ergonomic
designs for ease of grip while
scanning along the surface.

Contact Transducers (cont.)
• Contact transducers are available with
two piezoelectric crystals in one
housing. These transducers are called
dual element transducers.
• One crystal acts as a transmitter, the
other as a receiver.
• This arrangement improves near
surface resolution because the second
transducer does not need to complete
a transmit function before listening for
echoes.
• Dual elements are commonly
employed in thickness gauging of thin
materials.

Contact Transducers (cont.)
• A way to improve near surface
resolution with a single element
transducer is through the use of a
delay line.
• Delay line transducers have a plastic
piece that is a sound path that
provides a time delay between the
sound generation and reception of
reflected energy.
• Interchangeable pieces make it
possible to configure the transducer
with insulating wear caps or flexible
membranes that conform to rough
surfaces.
• Common applications include
thickness gauging and high
temperature measurements.

Transducers (cont.)
• Angle beam transducers
incorporate wedges to introduce
a refracted shear wave into a
material.
• The incident wedge angle is used
with the material velocity to
determine the desired refracted
shear wave according to Snell’s
Law)
• Transducers can use fixed or
variable wedge angles.
• Common application is in weld
examination.

Transducers (cont.)
• Immersion transducers are
designed to transmit sound
whereby the transducer and test
specimen are immersed in a
liquid coupling medium (usually
water).
• Immersion transducers
are manufactured with
planar, cylindrical or spherical
acoustic
lenses (focusing lens).

Instrumentation
• Ultrasonic equipment is usually purchased to satisfy specific
inspection needs, some users may purchase general
purpose equipment to fulfill a number of inspection
applications.
• Test equipment can be classified in a number of different
ways, this may include portable or stationary, contact or
immersion, manual or automated.
• Further classification of instruments commonly divides
them into four general categories: D-meters, Flaw
detectors, Industrial and special application.

Instrumentation (cont.)
• D-meters or digital thickness
gauge instruments provide
the user with a digital
(numeric) readout.
• They are designed primarily
for corrosion/erosion
inspection applications.
• Some instruments provide the user with both a
digital readout and a display of the signal. A
distinct advantage of these units is that they allow
the user to evaluate the signal to ensure that the
digital measurements are of the desired features.

• Flaw detectors are instruments
designed primarily for the
inspection of components for
defects.
• However, the signal can be
evaluated to obtain other
information such as material
thickness values.
• Both analog and digital display.
• Offer the user options of gating
horizontal sweep and
amplitude threshold.

• Industrial flaw detection
instruments, provide users
with more options than
standard flaw detectors.
• May be modulated units
allowing users to tailor the
instrument for their specific
needs.
• Generally not as portable as
standard flaw detectors.

• Immersion ultrasonic scanning
systems are used for automated
data acquisition and imaging.
• They integrate an immersion tank,
ultrasonic instrumentation, a
scanning bridge, and computer
controls.
• The signal strength and/or the time-
of-flight of the signal is measured
for every point in the scan plan.
• The value of the data is plotted
using colors or shades of gray to
produce detailed images of the
surface or internal features of a
component.

Images of a Quarter Produced With an Ultrasonic
Immersion Scanning System
Gray scale image produced using
the sound reflected from the front
surface of the coin
Gray scale image produced using the
sound reflected from the back surface
of the coin (inspected from “heads” side)

Calibration Standards
Calibration is a operation of configuring the ultrasonic test
equipment to known values. This provides the inspector
with a means of comparing test signals to known
measurements.
Calibration standards come in a wide variety of material
types, and configurations due to the diversity of inspection
applications.
Calibration standards are typically manufactured from
materials of the same acoustic properties as those of the test
articles.
The following slides provide examples of specific types of
standards.

Calibration Standards (cont.)
Thickness calibration
standards may be flat or
curved for pipe and tubing
applications, consisting of
simple variations in
material thickness.
Distance/Area Amplitude
standards utilize flat bottom
holes or side drilled holes to
establish known reflector
size with changes in sound
path form the entry surface.
ASTM Distance/Area Amplitude
NAVSHIPS

Calibration Standards (cont.)
There are also calibration
standards for use in angle
beam inspections when
flaws are not parallel to
entry surface.
These standards utilized
side drilled holes, notches,
and geometric
configuration to establish
time distance and
amplitude relationships.
IIW
DSC DC Rhompas
SC
ASME Pipe Sec. XI

Qualification Standards
Qualification
standards differ from
calibration standards
in that their use is for
purposes of varying
proper equipment
operation and
qualification of
equipment use for
specific codes and
standards.
AWS Resolution
IOW Beam Profile
DC-dB Accuracy

Data Presentation
• Information from ultrasonic testing can be presented in a
number of differing formats.
• Three of the more common formats include:
• A-scan
• B-scan
• C-scan
These three formats will be discussed in the next few slides.

Data Presentation - A-scan
• A-scan presentation displays
the amount of received
ultrasonic energy as a function
of time.
• Relative discontinuity size can
be estimated by comparing the
signal amplitude to that from a
known reflector.
• Reflector depth can be
determined by the position of
the signal on the horizontal
sweep.
Time
Signal
Amplitude
Signal
Amplitude
Time

Data Presentation - B-scan
• B-scan presentations display a profile
view (cross-sectional) of a test specimen.
• Only the reflector depth in the cross-
section and the linear dimensions can be
determined.
• A limitation to this display technique is
that reflectors may be masked by larger
reflectors near the surface.

Data Presentation - C-scan
• The C-scan presentation displays a plan type view of the test
specimen and discontinuities.
• C-scan presentations are produced with an automated data
acquisition system, such as in immersion scanning.
• Use of A-scan in conjunction with C-scan is necessary when
depth determination is desired.
Photo of a Composite
Component
C-Scan Image of
Internal Features

Advantage of Ultrasonic Testing
• 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.
• 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 automated systems.
• Has other uses such as thickness measurements, in addition to
flaw detection.

Limitations of Ultrasonic Testing
• Surface must be accessible to transmit ultrasound.
• Skill and training is more extensive than with some other methods.
• 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
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.

Glossary of Terms
• Acoustical properties: ultrasonic material characteristics such as
velocity, impedance, and attenuation.
• ASTM: acronym for American Society for Testing and Materials.
This society is extensively involved in establishing standards for
materials and the testing of materials.
• Back reflection: a display signal that corresponds to the far
surface of a test specimen, side opposite to transducer when
testing with longitudinal waves.
• Band width: a range of frequencies either transmitted or
received, may be narrow or broad range.
• B-scan: presentation technique displaying data in a cross-
sectional view.

Glossary of Terms
• Calibration: a sequence of instrument control
adjustments/instrument responses using known values to verify
instrument operating characteristics. Allows determination of
unknown quantities from test materials.
• CRT: acronym for Cathode Ray Tube. Vacuum tube that utilizes
one or more electron guns for generating an image.
• C-scan: presentation technique that displays specimen data in a
plan type view.
• DAC (Distance Amplitude Correction-curves): a graphical method
of allowing for material attenuation. Percentage of DAC is often
used as a means of acceptance criteria.
• Discontinuity: an interruption in the physical structure of a
material, examples include fissures, cracks, and porosity.

Glossary of Terms
• IIW: calibration standard meeting the specification of the
International Institute of Welding.
• Longitudinal (Compression) waves: ultrasonic mode of propagation in
which the particle vibration is parallel to the direction of propagation.
• Near Surface Resolution: the ability of an ultrasonic system to display
reflectors located close to the entry surface.
• Pulse-echo: ultrasonic test method that utilizes reflected sound as a
means of collecting test data.
• Rayleigh (Surface) waves: ultrasonic mode of propagation where the
sound travels along the surface, particle vibration is elliptical.

Glossary of Terms
• Reflection: the changing in direction of sound waves as they strike a
surface.
• Snell’s Law: an equation of ratios used to determine incident or
refracted angle of sound, denotes angle/velocity relationship.
• Sweep display: horizontal line on the lower portion of the display,
often called the time base line.
• Through transmission: test technique in which ultrasound is
transmitted from one transducer and received by a separate
transducer on the opposite side of the test specimen.
• Wavelength: the distance that a sound wave travels as it completes
one cycle, normally measured in inches or millimeters.

Case Study – Ultrasonography of human
body.

For More Information
The Collaboration for
NDT Education
www.ndt-ed.org
The American Society
for Nondestructive
Testing
www.asnt.org

Unit 4 ultrasonic testing method

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