1. 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
2. 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
3. Course Objective
To study and understand the various Non Destructive
Evaluation and Testing methods, theory and their
industrial applications.
3
4. 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
5. 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
6. 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
8. UNIT V: Topics
• 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 8
20. 20
INTERACTIONS OF X-RAYS WITH MATTER
The intensity of an x-ray beam is reduced by interaction with
the matter it encounters. This attenuation results from interactions of
individual photons in the beam with atoms in the absorber (patient).
The x-ray photons are either absorbed or scattered out of the beam. In
scattering, photons are ejected out of the primary beam as a result of
interactions with the orbital electrons of absorber atoms.
21. 21
In the case of a dental x-ray beam, Three mechanisms exist where these
interactions take place.
(1) Coherent scattering
(2) Compton scattering
(3) photoelectric absorption.
22. 22
COHERENT SCATTERING
Coherent Scattering (also know as classical scattering and Thompson
Scattering) may occur when a low-energy incident photon passes near an outer
electron of an atom (which has a low binding energy). The incident photon
interacts with the electron in the outer-shell by causing it to vibrate momentarily at
the same frequency as the incoming photon. The incident photon then ceases to
exist. The vibration causes the electron to radiate energy in the form of another x-
ray photon with the same frequency and energy as in the incident photon. In
effect, the direction of the incident x-ray photon is altered. This interaction accounts
for only about 8% of the total number of interactions (per exposure) in a dental
examination. Coherent scattering contributes very little to film fog because the total
quantity of scattered photons is small and its energy level is too low for much of it to
reach the film.
23. 23
Compton scattering occurs when a photon interacts with an
outer orbital electron, which receives kinetic energy and recoils
from the point of impact. The incident photon is then deflected by its
interaction and is scattered from the site of the collision. The energy
of the scattered photon equals the energy of the incident photon
minus the kinetic energy gained by the recoil electron plus its
bonding energy. As with photoelectric absorption, Compton
scattering results in the loss of an electron and ionization of the
absorbing atom.
Compton scattering
24. 24
Scattered photons travel in all directions. The higher the energy of
the incident photon, however, the greater the probability that the angle of
scatter of the secondary photon will be small and its direction will be
forward. Approximately 30% of the scattered photons formed during a
dental x-ray exposure (primarily from Compton scattering) exit the patient’s
head. This is advantageous to the patient because some of the energy of the
incident x-ray beam escapes the tissue, but it is disadvantageous because it
causes nonspecific film darkening (or fogging of the film). Scattered
photons darken the film while carrying no useful information to it
because their path is altered.
26. 26
Photoelectric Absorption
Photoelectric absorption occurs when an incident photon collides
with an inner-shell electron in an atom of the absorbing medium resulting in
total absorption and the incident photon ceases to exist. The electron is
ejected from its shell, resulting in ionization and becomes a recoil electron
(photoelectron). The kinetic energy imparted to the recoil electron is equal
to the energy of the incident photon minus that used to overcome the
binding energy of the electron. In the case of atoms with low atomic
numbers (e.g. those in most biologic energy of the incident photon. Most
Photoelectric interactions occur in the K shell because the density of the
electron cloud is greater in this region and a higher probability of
interaction exists. About 30% of photons absorbed from a dental x-ray
beam are absorbed by the photoelectric process.
27. 27
An atom that has participated in photoelectric interaction is
ionized. This electron deficiency (usually in the K shell) is instantly filled,
usually by an L- or M- shell electron, with the release of characteristic
radiation. Whatever the orbit of the replacement electron, the
characteristic photons generated are of such low-energy that they are
absorbed within the patient and do not fog the film.
28. 28
The frequency of photoelectric interaction varies directly with
the third power of the atomic number of the absorber. For example,
because the effective atomic number of compact bone (Z = 7,4), the
probability that a photon will be absorbed by a photoelectric interaction
in bone is approximately 6.5 times greater than in an equal distance of
water. This difference is readily seen on dental radiographs. It is this
difference in the absorption that makes that production of a radiographic
image possible.
36. 36
Film and Filmless Technique (Digital)
Industrial X-ray testing techniques can generally be divided into
conventional and digital methods. With film techniques, the image
information is captured by a film that is radiation sensitive on both sides.
After the exposure the film is processed by a chemical treatment, either
manually or fully automated by a film processing machine.
Film viewing and evaluation is done by using special
illuminators. The optical density of any point of the film can be
measured by densitometers. Areas that represent too thick walls to show
the minimum required optical densities cannot be evaluated initially.
37. 37
The same applies to areas with too high densities representing
too thin walls. These areas require additional films with suitable
densities. This can be achieved by using several films with different
sensitivities in one light protective bag (multi film technique). This
increases the so called covered thickness range, which is the maximum
wall thickness difference that can be captured with one exposure.
38. 38
Usually, films are put between two metal screens (mostly lead), in order
to reduce the disturbing influence of scattered radiation and to intensify the image
building radiation.
The evaluation of visible discontinuities is -especially for castings- done
by comparison with reference radiographs. The discontinuities are classified by
their types and sizes.
Radiographic testing with film is characterized by a complex work of
standards that have been under development for decades. These standards define
rules for the execution of tests, qualification of personnel, properties and
verifications of used tools and devices and the evaluation of films. In most cases
European standards (e.g. EN 17636 for weld inspection or EN 12681-1 for
inspection of castings) or US standards according to the ASME Code are
postulated.
39. 39
The advantages of the film technique are a much larger range of
applications and lower investment costs. X-ray films can be cut to the
required sizes, are flexible, lightweight and easy to place. The image
quality of thick-walled objects is much better than with digital methods.
X-ray films can be digitized. This offers an easy alternative for archiving
and copying.
The disadvantages of film radiography are the high material
costs because of film and chemistry consumption as well as the missing
real-time imaging. The result of an exposure cannot be discovered before
film processing.
40. 40
With digital techniques the image information is captured by a
radiation sensitive detector. There is a distinction between detectors that
are directly read out (e.g. rigit flat panels) and detectors that are read out
by scanners, so called CR systems (computed radiography systems) with
flexible storage imaging plates.
Signals of detectors with direct read-out are converted to gray
value images that can be displayed on monitors. Storage imaging plates
have to be read out by special scanners before a digital image is
produced.
42. 42
The sensitivity of digital detectors is much higher for low energy
radiation (e.g. scattered radiation) than for the image building high energy
radiation. As a result, the (low energy) scattered radiation produced in the
test object causes high counting rates that decrease contrast and image
quality. This effect is much lower with film techniques.
As primary energies for the inspection of thin-walled or lighter
objects are lower, the detectability of discontinuities is comparable
between film and digital techniques. But the thicker the walls and the
denser the material, the higher is the required radiation energy, which
means, that the achievable image quality is more and more reduced with
digital techniques in comparison to film techniques.
43. 43
The advantages of digital techniques are
•The operating costs are low because there are no consumables
necessary.
•Digital detectors are characterized by a high dynamic range, thus
large differences in radiation intensity and wall thicknesses can be
captured at the same time.
•The evaluation of X-ray images can be supported by computerized
image enhancement.
•Many digital systems are real-time capable. Therefore test areas can
be moved in the live image by manipulators.
•Image archiving is easier and more comfortable.
44. 44
The disadvantage of digital techniques
•High investment costs
•For both flat panel detectors and storage imaging plates the necessary
effort for the preparation of exposures to reduce scattered radiation is
higher than in film radiography. This applies particularly, if the detector
is not completely covered by the test object (Example: ellipse
technique for welds or inspection of small castings).
•For complex shaped objects with large differences in wall thickness it
is often not possible to reduce the scattered radiation generated inside
the object sufficiently, in order to produce an image that can be
evaluated.
45. 45
Types and use of filters and screens
Radiation filters
When a metal plate, usually lead or copper, is placed between the
tube window and the object, radiation “hardening” occurs leading to a
lower image contrast. This may be counter-balanced by a metal filter
placed immediately behind the object (i.e. between object and film). This
filter will cause the (softer) scattered radiation passing through the object
to be absorbed by the filter to a greater extent than the primary (harder)
radiation.
This also improves the image quality. If the edges of an object
being radiographed are not close to the film considerable scatter of the
primary radiation can occur, leading to fogging. This scatter can be
prevented by positioning sheets of lead foil between the object and the film
as illustrated in this figure.
46. 46
Reducing the contrast by filtration is also desirable when a radiographic
image of an object of widely varying thicknesses has to be obtained on a
single film see section 18.2.
Typical filter thicknesses are :
0.1 – 0.25 mm lead for 300 kV X-rays
0.25 – 1.0 mm lead for 400 kV X-rays
47. 47
Lead screens
Steel and copper screens
Fluorescent screens
Fluorescent salt screens
Fluorometallic screens
To utilise more of the available radiation energy, the film is
sandwiched between two intensifying screens. Different types of
material are being used for this purpose.
Intensifying screens
48. 48
The radiographic image is formed by only approximately 1 %
of the amount of radiation energy exposed at the film. The rest passes
through the film and is consequently not used. To utilise more of the
available radiation energy, the film is sandwiched between two
intensifying screens. Different types of material are being used for this
purpose.
49. 49
Intensifying screens are made up of two homogeneous sheets of
lead foil (stuck on to a thin base such as a sheet of paper or cardboard)
between which the film is placed: the so called front and back screens.
The thickness of the front screen (source side) must match the
hardness of the radiation being used, so that it will pass the primary
radiation while stopping as much as possible of the secondary radiation
(which has a longer wavelength and is consequently less penetrating).
The lead foil of the front screen is usually 0.02 to 0.15 mm
thick. The front screen acts not only as an intensifier of the primary
radiation, but also as an absorbing filter of the softer scatter, which
enters in part at an oblique angle, see figure 2-6. The thickness of the
back screen is not critical and is usually approx. 0.25 mm.
50. 50
The surface of lead screens is polished to allow as close a
contact as possible with the surface of the film. Flaws such as scratches
or cracks on the surface of the metal will be visible in the radiograph and
must, therefore, be avoided.
There are also X-ray film cassettes on the market with built-in
lead screens and vacuum packed to ensure perfect contact between
emulsion and lead foil surface.
Figure clearly show the positive effect of the use of lead screens.
Summarizing, the effects of the use of lead screens are :
• improvement in contrast and image detail as a result of reduced scatter
• decrease in exposure time
69. 69
Fluoroscopy is an imaging technique that uses X-rays to
obtain real-time moving images of the interior of an object. In its
primary application of medical imaging, a fluoroscope allows
a physician to see the internal structure and function of a patient,
so that the pumping action of the heart or the motion
of swallowing, for example, can be watched. This is useful for
both diagnosis and therapy and occurs in
general radiology, interventional radiology, and image-
guided surgery.
Fluoroscopy
70. 70
In its simplest form, a fluoroscope consists of an X-ray
source and a fluorescent screen, between which a patient is placed.
However, since the 1950s most fluoroscopes have included X-ray
image intensifiers and cameras as well, to improve the image's
visibility and make it available on a remote display screen. For
many decades, fluoroscopy tended to produce live pictures that
were not recorded, but since the 1960’s, as technology improved,
recording and playback became the norm.
The original difference was that radiography fixed still
images on film whereas fluoroscopy provided live moving
pictures that were not stored. However, t
day radiography, CT, and fluoroscopy are all digital
imaging modes with image analysis software and data storage
and retrieval.
83. 83
Computed Radiography (CR) is a digital imaging and
diagnosis technology that uses a special fluorescence plate called
“photostimulable phosphor” instead of the conventional X-ray
films to process X-ray images in a short time with high sensitivity.
When an X-ray is irradiated to the plate, electrons
generated in the plate are accumulated. A laser beam then scans
(excites) the image formed on the phosphor plate, causing visible
light to be emitted according to the amount of accumulated X-rays.
A photomultiplier tube is then used to convert this weak visible
light into electrical signals, which are then digitally processed to
reconstruct an image.
85. 85
Computed tomography (CT) is an imaging procedure that
uses special x-ray equipment to create detailed pictures, or scans, of
areas inside the body. It is sometimes called computerized
tomography or computerized axial tomography (CAT).
The term tomography comes from the Greek words tomos (a
cut, a slice, or a section) and graphein (to write or record). Each
picture created during a CT procedure shows the organs, bones, and
other tissues in a thin “slice” of the body. The entire series of
pictures produced in CT is like a loaf of sliced bread—you can look
at each slice individually (2-dimensional pictures), or you can look
at the whole loaf (a 3-dimensional picture). Computer programs are
used to create both types of pictures.
86. 86
Modern CT machines take continuous pictures in a helical
(or spiral) fashion rather than taking a series of pictures of
individual slices of the body, as the original CT machines
did. Helical CT (also called spiral CT) has several advantages over
older CT techniques: it is faster, produces better quality 3-
D pictures of areas inside the body, and may detect small
abnormalities better.
87. 87
CT scanners use a rotating X-ray tube and a row of
detectors placed in the gantry to measure X-ray attenuations by
different tissues inside the body. The multiple X-
ray measurements taken from different angles are then processed
on a computer using reconstruction algorithms to
produce tomographic (cross-sectional) images (virtual "slices") of
a body. The use of ionizing radiations sometimes restricts its use
owing to its adverse effects. However, CT can be used in patients
with metallic implants or pacemakers
where MRI is contraindicated.
88. 88
In addition to its use in cancer, CT is widely used to help
diagnose circulatory (blood) system diseases and conditions, such
as coronary artery disease (atherosclerosis), blood vessel
aneurysms, and blood clots; spinal conditions; kidney and bladder
stones; abscesses; inflammatory diseases, such as ulcerative
colitis and sinusitis; and injuries to the head, skeletal system, and
internal organs. CT imaging is also used to detect abnormal brain
function or deposits in adult patients
with cognitive impairment who are being evaluated for
Alzheimer’s disease and other causes of cognitive decline.
90. 90
Electron beam tomography
Electron beam tomography (EBT) is a specific form of CT
in which a large enough X-ray tube is constructed so that only the
path of the electrons, travelling between the cathode and anode of
the X-ray tube, are spun using deflection coils. This type had a
major advantage since sweep speeds can be much faster, allowing
for less blurry imaging of moving structures, such as the heart and
arteries. Fewer scanners of this design have been produced when
compared with spinning tube types, mainly due to the higher cost
associated with building a much larger X-ray tube and detector
array and limited anatomical coverage.
