Non-destructive testing (NDT) involves various techniques used to evaluate materials, components, or systems without damaging them. Common NDT methods described in the document include visual inspection, liquid penetrant testing, magnetic particle testing, thermography, radiography, eddy current testing, ultrasonic testing, and acoustic emission testing. Each method has advantages and limitations for detecting surface or internal flaws depending on the material and component being tested. NDT plays an important role in quality control and reliability across various industries.

1. UNIT-3
NON DESTRUCTIVE
TESTING

3. What is NDT?
• Non-destructive testing (NDT) is a wide group
of analysis techniques used in science and
technology industry to evaluate the properties
of a material, component or system without
causing damage.
• The terms non-destructive examination
(NDE), non-destructive inspection (NDI), and
non-destructive evaluation (NDE) are also
commonly used to describe this technology.

4. • Because NDT does not permanently alter the
article being inspected, it is a highly valuable
technique that can save both money and time
in product evaluation, troubleshooting, and
research.

5. • NDT does not directly measure mechanical
properties but they are used to locate defects or
flaws in the component.
• Flaws reduce useful life of component resulting
in premature failure even with a sound design
and proper selection of materials.
• To obtain high level of reliability , defect should
be absent or at minimum level.
• NDT is carried out periodically.
• Replacement of component before its premature
failure to avoid dangerous results.

6. Applications of NDT
• NDT is commonly used in forensic
engineering, mechanical engineering,
petroleum engineering, electrical engineering,
civil engineering, systems engineering,
aeronautical engineering, medicine, and art.
• Innovations in the field of non-destructive
testing have had a profound impact on
medical imaging, including on
echocardiography, medical ultrasonography,
and digital radiography.

7. DIFFERENT NDT METHODS
• VISUAL INSPECTION
• LIQUID/DYE PENETRATION TEST
• MAGNETIC PARTICLE TEST
• THERMOGRAPHY TEST
• RADIOGRAPHY TEST
• EDDY CURRENT TEST
• ULTRASONIC TEST
• ACOUSTIC EMISSION TEST

8. VISUAL INSPECTION
Visual Inspection is one of the most widely used
Non-Destructive Testing methods for the
detection of discontinuities before they cause
major problems, e.g. poor welding, surface
defects, corrosion pits, general condition,
degradation, blockages and foreign materials.

9. Generally, almost any specimen can be visually
examined to determine the accuracy of its
fabrication. • For example, visual inspection can
be used to determine whether the part was
fabricated to the correct size, whether the part
is complete, or whether all of the parts have
been appropriately incorporated into the device.

10. Types of Visual Inspection
1. Unaided Visual Inspection
2.Aided Visual Inspection

11. Unaided Visual Inspection
• It is also Known as Direct Visual Inspection
• It can be accomplished with the help of naked
eye
• It can done with out the help of optical aids
• Defects can be detected are – Absence of
cracks, Corrosion layer, surface porosity,
Misalignment of parts

12. Aided Visual Inspection
• It is also known as Indirect Visual Inspection
• It is performed using optical instruments
• This will identify the defects which cannot
detect with human eye
• It permits visibility to areas are not accessible
to human eye

13. Tools Used in Visual Inspection
• Mirrors
• Magnifying Glasses
• Microscopes
• Borescope
• Endoscope

14. Magnifying Mirrors
• It is also known as concave spherical mirrors
• It is used to magnify the areas which are not
accessible to human eye.

15. Magnifying Glass
• It is also called as Hand Lens
• This lens is used to produce a magnified Image
• Magnification depends upon the position
where it is being placed between the human eye
and the object
• For higher power magnification, double or
multiple lenses are used

16. Microscope
Microscope is used to magnify the image of a
small object
Borescope
• Which is used to inspect the inside of a narrow
tube
• It is a flexible tube with an eyepiece at one
end and objective lens at another end
• Light is passed through the lens and to obtain
a clear image

17. Endoscope
• It is bit superior than borescope
• Magnification factor of 10X is obtained
• Available up to smaller dia. of 1.7 mm and
length up to 100-150mm

18. Applications of Visual Inspection
• It is used to inspect whether there is a
misalignment of parts in the equipment
• It checks for corrosion, erosion, cracks and
deformities of machine components
• It inspect the plant components for any
leakage or abnormal operation
• It is used to identify the defects in weld ments

19. Limitations of Visual Inspections
• Can identify only large discontinuities
• Limited to surface discontinuities
• Skilled labour required
• Result depend on the eye resolution of the
inspector
• It may cause eye fatigue to the inspector

20. Material factors that affect Visual Testing
• Surface Condition – Cleanliness – Colour –
Texture
• Physical Conditions – Specimen Condition –
Shape and Size – Temperature
• Environmental Factors – Atmosphere –
Cleanliness – Humidity and Temperature –
Safety
• Physiological Factors – Physical Comfort –
Health , mental attitude

21. Dye Penetrant Inspection
• Invisible cracks, porosity and other defects on
the surface of components easily detected by
this technique.
• Components may be ferrous, nonferrous,
plastic, glass or ceramic.
Procedure
1. Cleaning of surface.
2. Drying of surface.

22. 3.Applying dye-penetrant on clean and dry surface.
It is allowed to penetrate in surface flaws.
i) Liquid Soluble Penetrant
ii) Fluroscent
4.Removing excess penetrant by soft or clean
cotton.
5.Applying developer on surface. This pulls out dye
from flaws and flaws are revealed by colour of dye.
Instead of developer, fine developing powder or talc
powder can be sprinkled on the surface.

24. Advantages of Dye Penetrant Inspection
• This test can be applied to almost any type of
metals, non-metals, magnetic or non magnetic
type.
• Simple to utilize and control.
• Results of test can be interpreted fastly.
• Cost of test is very less as it does not require
any instrument or electronic display units.

25. Disadvantages of Dye Penetrant Inspection
• Cleaning of components is must before and
after testing to avoid rusting
• Misleading results may be obtained in case of
components with surface films and coatings
• Only surface defects can be detected
• Test is not applicable for powder metallurgical
components

26. Magnetic Particle (Magnaflux) Inspection
• It is used to detect various kinds of flaws in
ferromagnetic components such as weldings,
castings, forgings of iron and steel.
• Component to be inspected for flaws is
magnetized.
• In dry method of inspection special fine
ferromagnetic powder is applied on surface .

27. • This test is a very fast method of inspection
and often used to test aerospace components
and automobile parts.
• This test is generally used to detect internal
cracks like shrinkage cavities, hot tears, zones
of corrosion and non-metallic inclusions

28. Magna flux Test Procedure:-
• Cleaning Surface
• Magnetization
• Application of ferromagnetic Powder
• Observation and Inspection
• Demagnetization

30. Advantages of Magnaflux Test
• Sub-surface cracks can be easily detected
• Almost any shaped and sized component can
be tested for defects
• Instruments are portable and easy to handle
• Highly sensitive method to detect small and
shallow surface cracks

31. Disadvantages of Magnaflux Test
• Method is applicable only to ferromagnetic
materials
• Surface plating or thin paint coating affect the
sensitivity of the test
• After testing, demagnetization is a must
• Local heating and sparking is possible during
test hence proper care must be taken

32. Thermography test
Infrared thermography is equipment or method,
which detects infrared energy emitted from
object, converts it to temperature, and displays
image of temperature distribution. The image of
temperature distribution is called infrared
thermograph and the method to be called as
infrared thermography.

33. Principle
Every object whose surface temperature is
above absolute zero radiates energy at a
wavelength corresponding to its surface
temperature. Utilizing our highly sensitive
infrared cameras, it is possible to convert this
radiated energy into a thermal image of the
object being surveyed .

34. THERMOGRAPHIC CAMERA
The camera converts radiated heat energy into
an electrical signal which is then displayed on
the monitor as a real-time heat image of the
object being scanned.

35. Overall equipment setup

36. ADVANTAGES
It is a non-contact type technique.
A large surface area can be scanned in no time.
Presented in visual & digital form.
Software back-up for image processing and
analysis.

37. DISADVANTAGES
Cost of instrument is relatively high.
 Unable to detect the inside temperature if the
medium is separated by glass/polythene
material etc.
Difficult to interpret even with experience
Training and staying proficient is time
consuming

38. • Testing is not viable during periods of adverse
weather (rain or wind).
• Testing can be adversely affected by several
surface conditions such as
Water
Wearing
Discolouration
Crack sealant
Strong wind, etc.,

39. APPLICATIONS
Printed circuit board evaluation and
troubleshooting.
Thermal mapping of semiconductor device
services
Circuit board component evaluation
Production-type inspection of bonded structures
Inspection of hybrid microcircuits
Inspection of solder joints

40. Radiography Test
• NDT method that utilizes x-rays or gamma
radiation to detect discontinuities in materials,
and to present their images on recording
medium.
• This includes X-rays, gamma rays and radio-
isotopes. This method is used to check internal
cracks, defects in materials which are made by
casting, welding, forging.
• Nowadays, radiography techniques are finding
more extensive applications in the field of
physical metallurgy and in the treatment of
various diseases.

41. • Rays are absorbed by the materials through
which they are passed in the proportion of
their density. The rays, after passing through
the components, show a picture on a
fluorescent screen or on a photographic plate.
• The cracks, blow holes and cavities appear
lighter, whereas inclusions of impurities
appear darker than the metal component.
• Developed photographic film show lighter and
darker areas to represent the radiograph of
defects in the component.

43. Advantages of Radiography Test
• X-ray radiography is highly sensitive, fast
method of finding defects
• X-ray radiography is suitable for various
applications due to its adjustable energy levels
• Gamma ray radiography has high penetrating
power hence can be used for more denser and
thicker materials
• A number of samples can be inspected at a
time by gamma ray radiography

44. Disadvantages of Radiography Test
• X-ray radiography can be applied for thinner
components due to its less penetrating power
• X-ray radiography allows only one component
to be tested at a time
• X-ray radiography involves high initial cost
• X-ray and gamma ray radiography involve
radiations which are hazardous to living
beings
• Trained operators are required

45. Eddy Current Testing
Basic Principle
When coil carrying alternating current is
brought near metallic specimen, eddy currents
are developed in specimen due to
electromagnetic induction. EMI depend on
i)Magnitude and frequency of alternating
current flowing in coil.
ii) Electrical conductivity of specimen.
iii) Magnetic permeability of specimen.

46. iv)Shape of specimen.
v)Relative positions of coil and specimen.
vi)Microstructure and hardness of Specimen.
vii)Amount and type of defects in the specimen.

49. Advantages ECT
• Test is quick and less time consuming
• Test can be automated easily
• Permanent record of test results can be easily
available
• Test is versatile and can be used for various
applications

50. Disadvantages of ECT
• The instrument standardization and
calibration is necessary from time to time
• Instruments and display units are costly
• Test can be applied to components of limited
size and shape

51. 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.

52. 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.

53. Spectrum of sound
Frequency range Description Example
(Hz)
0 - 20 Infrasound Earthquake
20 – 20,000 Audible sound Speech,music
> 20,000 Ultrasound Quartz crystal

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

55. • 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 travel time of the sound can be measured
and this provides information on the distance
that the sound has travelled.

56. • 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

57. 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.

58. • D-meters or digital thickness gauge
instruments provide the user with a digital
(numeric) readout.
• They are designed primarily for corrosion
inspection applications.
• 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.

59. • 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.

60. 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

61. 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.

62. • 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.

63. Angle beam transducers
• Angle beam transducers incorporate wedges
to increase the versatility of transducer
enabling it to become an angle transducerof
45,60 or 70 degrees.
•Transducers can use fixed or variable wedge
angles.
•Common application is in weld examination.

64. Immersion transducers
• 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).

65. Calibration
• 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.

66. • 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

67. •A-scan presentation displays the amount of
received ultrasonic energy as a function of time.

68. • 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.

69. The C-scan presentation displays a plan type
view of the test specimen and discontinuities.

70. 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 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)

71. • In pulse-echo testing, a transducer sends out a
pulse of energy and the same 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.

72. Through-Transmission
• 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.

73. 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.

74. • 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 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.

75. Advantage of Ultrasonic Testing
•Sensitive to both surface and subsurface discontinuities.
•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.
•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.

76. Limitations of Ultrasonic Testing
•Surface must be accessible to transmit ultrasound.
•Due to manual operation, careful attention and
highly skilled operators are required
•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.

77. Application
• Flaw detection(cracks,porosity etc.,)
• Estimation of void content in composites and
plastics
• Thickness measurement of pipelines,reactor
vessels

78. ACOUSTIC EMISSION TESTING
• Acoustic emission may be defined as a
transient elastic wave generated by the rapid
release of energy within a material
• When a structure is subjected to an external
stimulus (change in pressure,load or
temperature) ,localized source trigger the
release of energy in the form of stress waves,
which propogate to the surface and recorded
by sensors.

80. Testing process
• Detection of AE
• Processing of AE signals
• Displaying AE signals
• Locating AE signals

81. Testing process

82. Detection of AE
• As crack grows a number of emissions are
released
• When the AE wave arrives at the surface of
test specimen minute movement of surface
molecules occur
• The function of AE sensor is to detect this
movement and convert it into electrical signal

83. Processing of AE signals
The small voltage generated by the sensor is
amplified and radio frequency signal is
transmitted to the computer
The RF signal is split into discrete waveforms
These waveforms are then prescribed by
characteristics such as amplitude,rise
time,absolute energy

84. Displaying AE signals
The collected wave forms can then be displayed
in two ways
One,function of waveform parameters
Two,as collected waveform
Most AE tests currently only record the
waveform parameters and ignore the collected
waveform, mainly due to large amount of
computing memory it uses

85. Locating AE signals
The predominant method of source location is
based on the time difference between the
arrival of individual AE signals

86. Advantages
High sensitivity
Early and rapid detection of defects,flaws,cracks
etc.,
Real time monitoring
Minimization of plant downtime for
inspection,no need for scanning the whole
structural surface.

87. Disadvantages
• Acoustic emission systems can only estimate
qualitatively how much damage is in the
material and approximately how long the
components will last .So,other methods are
still needed to do more thorough
examinations and provide quantitative results.

88. Applications
• Inspect and monitor pipelines,storage
tanks,bridges and variety of composite and
ceramic components.
• Also used in process control applications such
as monitoring welding process