UNIT 4.ppt

Karpagam Institute of Technology
Coimbatore-105
Department of Mechanical Engineering
Course Code with Name: ME8097 –Non Destructive Testing and
Evaluation
Staff Name/Designation: VIJAYAN S N/AP
Department: Mechanical Engineering
Year/Semester: IV/VII
1

Course Syllabus
UNIT I OVERVIEW OF NDT 9
NDT Versus Mechanical testing, Overview of the Non Destructive Testing Methods for the detection of
manufacturing defects as well as material characterisation. Relative merits and limitations, Various
physical characteristics of materials and their applications in NDT., Visual inspection – Unaided and
aided.
UNIT II SURFACE NDE METHODS 9
Liquid Penetrant Testing - Principles, types and properties of liquid penetrants, developers, advantages
and limitations of various methods, Testing Procedure, Interpretation of results. Magnetic Particle
Testing- Theory of magnetism, inspection materials Magnetisation methods, Interpretation and
evaluation of test indications, Principles and methods of demagnetization, Residual magnetism.
UNIT III THERMOGRAPHY AND EDDY CURRENT TESTING (ET) 9
Thermography- Principles, Contact and non contact inspection methods, Techniques for applying
liquid crystals, Advantages and limitation - infrared radiation and infrared detectors, Instrumentations
and methods, applications. Eddy Current Testing-Generation of eddy currents, Properties of eddy
currents, Eddy current sensing elements, Probes, Instrumentation, Types of arrangement,
Applications, advantages, Limitations, Interpretation/Evaluation.
UNIT IV ULTRASONIC TESTING (UT) AND ACOUSTIC EMISSION (AE) 9
Ultrasonic Testing-Principle, Transducers, transmission and pulse-echo method, straight beam and
angle beam, instrumentation, data representation, A/Scan, B-scan, C-scan. Phased Array Ultrasound,
Time of Flight Diffraction. Acoustic Emission Technique –Principle, AE parameters, Applications
UNIT V RADIOGRAPHY (RT) 9
Principle, interaction of X-Ray with matter, imaging, film and film less techniques, types and use of
filters and screens, geometric factors, Inverse square, law, characteristics of films - graininess, density,
speed, contrast, characteristic curves, Penetrameters, Exposure charts, Radiographic equivalence.
Fluoroscopy- Xero-Radiography, Computed Radiography, Computed Tomography
2

Course Objective
To study and understand the various Non Destructive
Evaluation and Testing methods, theory and their
industrial applications.
3

Course Outcome
• Explain the fundamental concepts of NDT
• Discuss the different methods of NDE
• Explain the concept of Thermography and
Eddy current testing
• Explain the concept of Ultrasonic Testing and
Acoustic Emission
• Explain the concept of Radiography
4

Program Outcomes
1. An ability to apply knowledge of mathematics and engineering sciences to
develop mathematical models for industrial problems.
2. An ability to identify, formulates, and solve complex engineering problems.
with high degree of competence.
3. An ability to design and conduct experiments, as well as to analyze and
interpret data obtained through those experiments.
4. An ability to design mechanical systems, component, or a process to meet
desired needs within the realistic constraints such as environmental, social,
political and economic sustainability.
5. An ability to use modern tools, software and equipment to analyze
multidisciplinary problems.
6. An ability to demonstrate on professional and ethical responsibilities.
7. An ability to communicate, write reports and express research findings in a
scientific community.
8. An ability to adapt quickly to the global changes and contemporary practices.
9. An ability to engage in life-long learning.
5

Program Specific Outcomes
• An ability to identify, analyze and solve engineering
problems relating to mechanical systems together
with allied engineering streams.
• An ability to build the nation, by imparting
technological inputs and managerial skills to become
Technocrats and Entrepreneurs, build the attitude of
developing new concepts on emerging fields and
pursuing advanced education.
6

UNIT IV
ULTRASONIC TESTING (UT) AND
ACOUSTIC EMISSION (AE)
7

UNIT IV: Topics
• Ultrasonic Testing-Principle, Transducers, transmission and
pulse echo method.
• straight beam and angle beam, instrumentation, data
representation.
• A/Scan, B-scan, C-scan.
• Phased Array Ultrasound.
• Time of Flight Diffraction.
• Acoustic Emission Technique –Principle.
• AE parameters, Applications.
8

Video and Animation
9
IMMERSION TYPE
https://www.youtube.com/watch?v=2n4s66V_238
CONTACT TYPE
https://www.youtube.com/watch?v=UM6XKvXWVFA
DATA PRESENTATION
https://www.youtube.com/watch?v=9zS-_wUBCfw
https://www.youtube.com/watch?v=3jNtSqnhxBc
TOFD

11
Ultrasonic Testing
Ultrasonic Testing (UT) uses high frequency sound waves
(typically in the range between 0.5 and 15 MHz) to conduct
examinations and make measurements. Besides its wide use in
engineering applications (such as flaw detection/evaluation, dimensional
measurements, material characterization, etc.), ultrasonics are also used
in the medical field (such as sonography, therapeutic ultrasound, etc.).
In general, ultrasonic testing is based on the capture and
quantification of either the reflected waves (pulse-echo) or the
transmitted waves (through-transmission). Each of the two types is used
in certain applications, but generally, pulse echo systems are more useful
since they require one-sided access to the object being inspected.

Basic Principles
12
A typical pulse-echo UT inspection system consists of several
functional units, such as the pulser/receiver, transducer, and a display
device. A pulser/receiver is an electronic device that can produce high
voltage electrical pulses. Driven by the pulser, the transducer 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 an
electrical signal by the transducer and is displayed on a screen.

14
Advantages
It is sensitive to both surface and subsurface discontinuities.
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 highly accurate in determining the reflector position and
estimating its size and shape.
Minimal part preparation is required.
It provides instantaneous results.

15
Detailed images can be produced with automated systems.
It is nonhazardous to operators or nearby personnel and does not
affect the
material being tested.
It has other uses, such as thickness measurement, in addition to
flaw detection.
Its equipment can be highly portable or highly automated.

16
Disadvantages
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 the transfer of
sound energy into the 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
the characterization of flaws.

17
Ultrasonic Waves
1. Longitudinal Waves
2. Transverse Waves
3. Surface waves

19
Properties of Acoustic (Sound)Waves
Among the properties of waves propagating in isotropic solid materials are
wavelength, frequency, and velocity. The wavelength is directly proportional to the
velocity of the wave and inversely proportional to the frequency of the wave. This
relationship is shown by the following equation:
𝜆 = 𝑉/𝑓
Where;
𝜆 : wavelength (m)
𝑉 : velocity (m/s)
𝑓 : frequency (Hz)
The velocity of sound waves in a certain medium is fixed where it is a characteristic
of that medium. As can be noted from the equation, an increase in frequency will
result in a decrease in wavelength.

22
Reflection and Transmission Coefficients
Ultrasonic waves are reflected at boundaries where there is a
difference in acoustic impedances (𝑍) of the materials on each side of
the boundary. This difference in 𝑍 iscommonly referred to as the
impedance mismatch. The greater the impedance mismatch, the
greater the percentage of energy that will be reflected at the interface
or boundary between one medium and another.
The fraction of the incident wave intensity that is reflected
can be derived based on the fact that particle velocity and local
particle pressures must be continuous across the boundary. When the
acoustic impedances of the materials on both sides of the boundary
are known, the fraction of the incident wave intensity that is reflected

31
Ultrasonic Transducer
Types of ultrasonic Probes
1. Normal Probe
2. Angle Probe

33
Piezoelectric Transducers
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.

35
The active element of most acoustic transducers used today is a
piezoelectric ceramic, which can be cut in various ways to produce
different wave modes.
A large piezoelectric ceramic element can be seen in the image
of a sectioned low frequency transducer. The most commonly
employed ceramic for making transducers is lead zirconate titanate.
The thickness of the active element is determined by the
desired frequency of the transducer. A thin wafer element vibrates with
a wavelength that is twice its thickness.

36
Characteristics of Piezoelectric Transducers
The function of the transducer is to convert electrical
signals into mechanical vibrations (transmit mode) and
mechanical vibrations into electrical signals (receive mode).
Manyfactors, including material, mechanical and
electrical construction, and the external mechanical and electrical
load conditions, influence the behavior of a transducer.

38
To get as much energy out of the transducer as possible, an
impedance matching layer is placed between the active element
and the face of the transducer. Optimal impedance matching is
achieved by sizing the matching layer so that its thickness is 1/4 of
the desired wavelength.
This keeps waves that are reflected within the matching
layer in phase when they exit the layer. For contact transducers, the
matching layer is made from a material that has an acoustical
impedance between the active element and steel. Immersion
transducers have a matching layer with acoustical impedance
between the active element and water.

39
The backing material supporting the crystal has a great
influence on the damping characteristics of a transducer. Using a
backing material with impedance similar to that of the active
element will produce the most effective damping.
Such a transducer will have a wider bandwidth resulting in
higher sensitivity and higher resolution (i.e., the ability to locate
defects near the surface or in close proximity in the material). As
the mismatch in impedance between the active element and the
backing material increases, material penetration increases but
transducer sensitivity is reduced.

40
The bandwidth refers to the range of frequencies associated
with a transducer. The frequency noted on a transducer is the central
frequency and depends primarily on the backing material. Highly
damped transducers will respond to frequencies above and below the
central frequency.
The broad frequency range provides a transducer with high
resolving power. Less damped transducers will exhibit a narrower
frequency range and poorer resolving power, but greater penetration.

41
The central frequency will also define the capabilities of a
transducer. Lower frequencies (0.5MHz - 2.25MHz) provide
greater energy and penetration, while high frequency crystals
(15.0MHz - 25.0MHz) provide reduced penetration but greater
sensitivity to small discontinuities.

42
Transducer Types
Ultrasonic transducers are manufactured for a variety of
applications and can be custom fabricated when necessary. Careful
attention must be paid to selecting the proper transducer for the
application. It is important to choose transducers that have the
desired frequency, bandwidth, and focusing to optimize inspection
capability. Most often the transducer is chosen either to enhance the
sensitivity or resolution of the system.

43
Transducers are classified into two major groups
according to the application
Contact transducers
Immersion transducers

45
Dual element transducers
Delay line transducers
Angle beam transducers
Normal incidence shear wave transducers
Paint brush transducers

69
Phased Array Ultrasound (PAUT)
The ultrasonic system shall incorporate facilities for
detection of transverse defects, when it is clearly identified that the
weld process, parent material, application and environmental
condition may increase the risk for transversal type flaws

70
Types of focal configurations for linear array probes

71
MANUAL PAUT CONFIGURATIONS
A phased array probe can be configured to have a single
focal law (one angle), and then it is easily used, as might be any
single-element probe used in manual UT, where the operator simply
watches the A-scan display. This may be useful in some cases when
a project requires a “traditional” manual UT assessment.
Scanning techniques can be developed to use the phased
array probe in a hand-held, manually operated raster fashion with a
sectorial scan. Although E-scans could be used with manual raster
scanning, it would seem to be redundant. It is more likely that the S-
scan would be used with manual raster operation of the phased array
probe.

72
S-scan display with adjustable markers that can be used to
indicate the bottom and top of the test piece. With a scale in mm
that indicates a distance from the probe, the operator can estimate
the depth and approximate position of the source of the signal to
make a judgement as to its origin.

73
Manual scanning using an S-scan to locate indications

74
AUTOMATED APPLICATIONS OF PAUT
Mechanisation of weld inspections need not be as complex as
two or three axes of motion control using motorised actuation. The
simplest form of mechanisation would involve connecting an encoder
to the phased array probe and moving it along the weld by hand.
Thissimple “line scan” as it is called, has proven to be the most
popular option for phased array weld inspections.
The variations in standoff that result could be relatively small,
of the order of 2-3mm. But this can be improved upon, using a
straight-edge guide. Magnetic strips work well when inspecting steel
components.

75
Most Standards require that inspection be carried out from
both sides of the weld (when possible). When using a single
phased array probe, this requires two scans. However, some
phased array systems can be arranged to address two phased array
probes simultaneously.
The phased array instrument must then be configured to
collect the data with suitable parameter inputs to ensure that the
flaws located are rotated correctly (i.e. skew is 180° different
between the two probes). Single and dual phased array mounting
with encoders is illustrated in Figure

76
Single and dual probe mountings with encoders attached

77
When used with a guide strip the operator has good control on
the standoff and flaw positioning accuracy is significantly improved.
Having a solid guide strip to move against also tends to improve the
coupling, prevent stuttering motion (which can cause missing data
due to excessive speed) and generally speeds up the entire data
collection process by avoiding re-scans due to missed data and poor
coupling.

78
Mechanised scanning with a guide strip held in place with a magnet

79
Motorised motion control with solid mountings can add a
further degree of mechanisation to the process. Where high
production inspection of a uniformly shaped part is required, (such
as pipe girth welds), positioning rings can be used to facilitate
rapid mounting and dismounting of the scanning apparatus.
The scanning apparatus can be a simple, single or double
probe holder, or may be equipped to hold several phased array
probes in a single fixture for more complex scanning

80
Small diameter 2 PA probes Large diameter multi-probe pipe scanner

81
The image on the left has a quick-connect clam fixture, that
the carriage with probes, motor and encoder attach to, for small
diameter pipe (typically <12” diameter). On the right in Figure is the
underside of a system designed for high production pipeline
inspections.
The drive wheels seen at the bottom of the image connect to
a steel band that is clamped in place at the weld. It is often the same
band that is used by the automatic welding system to make the weld
being inspected. The image shows 2 phased array probes and 4
single element probes (used in T-R mode for transverse
flaw detection) plus a thermal sensor (top left) designed to monitor
wedge temperature.

82
Applications
RAIL
AEROSPACE
POWER GENERATION
CASTINGS
FORGINGS
PLATE
WELDING

83
Time of Flight Diffraction
Overview
Although time-of-flight diffraction (TOFD) can be used for
a variety of applications, its primary use is rapid weld testing of
circumferential and axial weld seams, also known as perpendicular
TOFD scanning.
Manual execution is possible with TOFD, however, it is
most commonly performed in combination with a recording device,
that is, an encoder or industrial scanner. To achieve code
compliance in North America, TOFD is often coupled with pulse-
echo or phased array techniques in order to cover the root and cap
regions of the weld.

84
TOFD Basic Theory
TOFD is usually performed using longitudinal waves as the primary
detection method. Ultrasonic sensors are placed on each side of the weld. One sensor
sends the ultrasonic beam into the material and the other sensor receives reflected and
diffracted ultrasound from anomalies and geometric reflectors. TOFD provides a wide
area of coverage with a single beam by exploiting ultrasonic beam spread theory
inside the wedge and the inspected material. When the beam comes in contact with
the tip of a flaw, or crack, diffracted energy is cast in all directions.

85
Measuring the time of flight of the diffracted beams enables accurate and reliable
flaw detection and sizing, even if the crack is off-oriented to the initial beam
direction. During typical TOFD inspections, A-scans are collected and used to
create B-scan (side view) images of the weld. Analysis is done on the acquisition
unit or in post-analysis software, positioning cursors to measure the length and
through-wall height of flaws.

86
TOFD System- Introduction
The TOFD technique is a fully computerized and automated system able
to scan, store, and evaluate indications in terms of height, length, and position
with a grade of accuracy never achieved by other ultrasonic techniques. TOFD
system consists of UT detector (Computer), transmitter, receiver, pre-amplifier,
encoder and cables. TOFD system is small, light, portable and accessible to
inspection position.

87
The principle and operation of TOFD:
The TOFD technique is based on diffraction of ultrasonic
waves on tips of discontinuities, instead of geometrical reflection on
the interface of the discontinuities. When ultrasound is incident at
linear discontinuity such as a crack, diffraction takes place at its
extremities in addition to the normal reflected wave. This diffracted
energy is emitted over a wide angular range and is assumed to
originate at the extremities of the flaw. The conventional UT relies
on the amount of energy reflected by the discontinuities.

88
The TOFD technique uses a pair of probes in a transmitter-
receiver arrangement. Usually longitudinal probes are applied with
an angle of incidence range of 45° to 70°. The diffracted signals are
received via the receiver probe and are evaluated with the
Ultrasonic System. The difference in the flight of the diffracted
wave fronts carry the information on the spatial relationship of the
tips of the defect and hence the extent of the defect. TOFD method
only evaluates diffracted echoes, which are 20dB less than the
reflected echoes.

89
Transmitter-Receiver arrangement of TOFD
Gray scale imaging techniques are applied to the RF (AC)
signal phases and enable weld integrity to be observed in real time.
The defects are shown like as shell pattern on CRT. A-scan signals
are stored in the memory together with location signals
TOFD – A Scan

90
Scanning is carried out externally by placing the two probes
located at equidistant over the weld centre. The scanned image is
often referred to as D-Scan
TOFD – D Scan of butt weld and defect

91
Advantages of TOFD: There are many advantages for using TOFD for weld
inspection.
1. High Probability of Flaw Detection (POD).
2. Lower False Call Rates (FCRs)
3. High Accuracy of Flaw Location Measurement.
4. High Accuracy of Flaw Sizing in Length.
5. Weld Integrity can be assessed on CRT in Real Time as probes scan and
acquisition of data.
6. All inspection Results/Data is Digitized and Stored so that the same can be
Recalled and Processed for In-Service Inspection.
7. In-service inspection avoids production loss.
8. As TOFD is a substitute for radiography, production is not interrupted since
evacuation of areas is not necessary.
9. Since the equipment is portable, it is possible to perform TOFD on all feasibly
accessible areas.
10. TOFD saves costs
11. By automatic system with the aid of computer and advanced soft wares it is
possible to evaluate signals very rapidly.
12. Most efficient for inspection of thick-walled vessels where X & Gamma ray
would require too much time .

92
Limitations of TOFD: TOFD suffers from certain limitations.
1. TOFD is insensitive to surface defects upto ½” deep. However, R/D
Tech’s equipment allows simultaneous combination of TOFD with
pulse-echo, which complements TOFD and covers the dead zones .
Also, Sonomatic Microplus of AEA Technology have succeeded in
reducing the dead zone to 2 mm.
2. For TOFD the gain must be very high, which produces a very high
back wall echo and it is not suitable for coarse-grained materials
3. TOD Technique is not effective at detecting and sizing defect lying
parallel to the inspection surface
4. High initial cost of TOFD Equipment.
5. The need of experienced and skilled operator.

93
TOFD Principle
Ultrasonic probes are positioned on either side of the weld,
one acting as a transmitter and the other a receiver. The longitudinal
sound beam may encounter obstacles along its path which cause
reflected and diffracted signals (figure 1 and figure 2). When the
probes are moved in a parallel motion along the weld, the resultant
waveforms are digitized, stored on hard disk and displayed on the
video-screen as a grey scale image (Figure 3). The image provides a
sectional view through the weld and can be used for accurate sizing
and monitoring of indications.

95
Data Storage and Reporting
All data collected with the TOFD system is stored for future
reference. Data can be made available on optical disc or CD upon
demand. Analysis software is also available should the client require
any further evaluation of the data. Read-only data and reports are
available in a format compatible with the most commonly used
inspection and maintenance data management systems. For standard
pre-service inspection, pre-formatted reports tailored to client and/or
authorities QA/QC requirements are provided.

96
Acoustic Emission Technique

98
Acoustic Emission Parameters

101
Advantages
•High sensitivity.
•Early and rapid detection of defects, flaws, cracks etc.
•Real time monitoring
•Cost Reduction
•Defective area location: only critical defects provide sustainable Acoustic
Emission sources.
•Minimization of plant downtime for inspection, no need for scanning the
whole structural surface.
•Minor disturbance of insulation.
•Application of Artificial Intelligence (AI) and Technological Packages:
Expert systems for evaluating the condition of metallic pressure systems and
tank bottoms based on the acquired experience of a huge number of tests are
world wide used.

UNIT 4.ppt

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