This document provides a summary of non-destructive testing (NDT) methods. It discusses various NDT techniques such as visual inspection, dye penetration testing, magnetic particle inspection, and ultrasonic testing. For each method, it explains the basic principles, testing procedures, advantages, and limitations. The document is a report submitted by a student to their professor on the topic of NDT, as indicated by the title and introduction. It aims to inform the reader about common NDT approaches through detailed descriptions of select techniques.

1. A
Report
on
NON DESTRUCTIVE TESTING
Submitted by
SAKSHYAM RAI
1403040093
3rd
YEAR
MECHANICAL SECTION-B
Submitted to
Mr. Lalit Rathee
Asst. Professor
Department of Mechanical Engineering
Inderprastha Engineering College
63 Site IV, Sahibabad Industrial Area,
Surya Nagar Flyover Road Sahibabad, Ghaziabad-U.P

2. 2
CONTENTS
1. Introduction 3
2. Principles 5
3. Different methods of NDT 6
3.1. Visual Inspection and optical microscopy test 7
3.2. Dye penetration test 8
3.3. Magnetic particle inspection 11
3.4. Ultrasonic testing 14
3.5. Radiographic testing 17
4. Applications of NDT 19
5. Advantages of NDT 20
6. Disadvantages of NDT 21
7. Conclusion 22
8. References 23

3. 3
1. INTRODUCTION
The current era is known as era of industrialisation and the growing industrial
development is a vital part of it. The requirements of mankind and industries
have increased and so are the products. The desired aspects have grown and that
is why we cannot compromise with the quality of the products. Mechanical
testing is one of the way to make sure that the required qualities are present in
the product or not. It also helps in selection of perfect materials for the
manufacturing of any specific product.
So we can say that Mechanical testing is a general term which refers to a broad
range of activity involved with the determination of mechanical pproperties and
behaviour of material, structures and machines. Typically it involves some type
of stimulus and measuring of response. Expanding on this definition,
mechanical testing is the process of applying forces, pressures displacements,
heat or similar stimuli to a mechanical system and then measuring its response.
Basically, mechanical testing is of two types, namely Destructive Testing and
Non Destructive Testing. Both the types have got their own advantages and
disadvantages, that we will discuss further. However, we shall be emphasizing
more on Non Destructive testing, being the topic of the report.

4. 4
NON DESTRUCTIVE TESTING
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. It is the process of
inspecting, testing, or evaluating materials, components or assemblies for
discontinuities, or differences in characteristics without destroying the
serviceability of the part or system.
In other words, when the inspection or test is completed the part can still be
used. 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. Common NDT methods
include ultrasonic, magnetic-particle, liquid penetrant, radiographic, remote
visual inspection (RVI), eddy-current testing, and low coherence
interferometry.
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 nondestructive testing have had a profound
impact on medical imaging, including on echocardiography, medical
ultrasonography, and digital radiography.
It is highly preferred for any purpose where failure of components can cause
severe hazards or economic loss.

5. 5
2. PRINCIPLES
NDT methods may rely upon use of electromagnetic radiation, sound, and
inherent properties of materials to examine samples. This includes some kinds
of microscopy to examine external surfaces in detail, although sample
preparation techniques for metallography, optical microscopy and electron
microscopy are generally destructive as the surfaces must be made smooth
through polishing or the sample must be electron transparent in thickness. The
inside of a sample can be examined with penetrating radiation, such as X-
rays, neutrons or terahertz radiation. Sound waves are utilized in the case of
ultrasonic testing. Contrast between a defect and the bulk of the sample may be
enhanced for visual examination by the unaided eye by using liquids to
penetrate fatigue cracks. One method (liquid penetrant testing) involves using
dyes, fluorescent or non-fluorescent, in fluids for non-magnetic materials,
usually metals. Another commonly used NDT method used on ferrous materials
involves the application of fine iron particles (either liquid or dry dust) that are
applied to a part while it is in an externally magnetized state (magnetic-particle
testing). The particles will be attracted to leakage fields within the test object,
and form on the objects surface. Magnetic particle testing can reveal surface &
some sub-surface defects within the part. Thermoelectric effect (or use of
the Seebeck effect) uses thermal properties of an alloy to quickly and easily
characterize many alloys. The chemical test, or chemical spot test method,
utilizes application of sensitive chemicals that can indicate the presence of
individual alloying elements. Electrochemical methods, such as electrochemical
fatigue crack sensors, utilize the tendency of metal structural material to oxidize
readily in order to detect progressive damage.
Analyzing and documenting a non-destructive failure mode can also be
accomplished using a high-speed camera recording continuously (movie-loop)
until the failure is detected. Detecting the failure can be accomplished using a
sound detector or stress gauge which produces a signal to trigger the high-speed
camera. These high-speed cameras have advanced recording modes to capture
some non-destructive failures.[5]
After the failure the high-speed camera will
stop recording. The capture images can be played back in slow motion showing
precisely what happen before, during and after the non-destructive event, image
by image.

6. 6
3. DIFFERENT METHODS OF NDT
NDT is divided into various methods of non destructive testing, each based on a
particular scientific principle. These methods may be further subdivided into
various techniques. The various methods and techniques, due to their particular
natures, may lend themselves especially well to certain applications and be of
little or no value at all in other applications. Therefore, choosing the right
method and technique is an important part of the performance of NDT.
 Acoustic emission testing (AE or AT)
 Dye penetrant inspection or Liquid penetrant Testing (PT or LPI)
 Electromagnetic testing (ET) or Electromagnetic Inspection (EMI)
 Alternating current field measurement (ACFM)
 Alternating current potential drop measurement (ACPD)
 Direct current potential drop measurement (DCPD)
 Eddy-current testing (ECT)
 Magnetic flux leakage testing (MFL)
 Magnetic-particle inspection (MT or MPI)
 Remote field testing (RFT)
 Endoscope inspection
 Guided wave testing (GWT)
 Hardness testing
 Impulse excitation technique (IET)
 Terahertz nondestructive evaluation(THz)
 Infrared and thermal testing (IR)
 Thermographic inspection
 Infrared thermal microscopy
 Laser testing
 Electronic speckle pattern interferometry
 Holographic interferometry
 Low coherence interferometry
 Profilometry
 Shearography
 Leak testing (LT) or Leak detection
 Absolute pressure leak testing (pressure change)
 Bubble testing
 Halogen diode leak testing
 Hydrogen leak testing
 Mass spectrometer leak testing
 Tracer-gas leak testing method Helium, Hydrogen and refrigerant gases
 Magnetic resonance imaging (MRI) and NMR spectroscopy

7. 7
 Near-infrared spectroscopy (NIRS)
 Optical microscopy
 Positive Material Identification (PMI)
 Radiographic testing (RT) (see also Industrial radiography and Radiography)
 Computed radiography
 Digital radiography
 Neutron Imaging
 SCAR (Small Controlled Area Radiography)
 X-ray computed tomography (CT)
 Resonant Inspection
 Resonant Acoustic Method (RAM) [14]
 Scanning electron microscopy
 Surface Temper Etch (Nital Etch)
 Ultrasonic testing (UT)
 Angle beam testing
 Thickness measurement
 Time of flight diffraction ultrasonics (TOFD)
 Time of Flight Ultrasonic Determination of 3D Elastic Constants (TOF)
 Vibration Analysis
 Visual inspection (VT)
 Pipeline video inspection
 Weight and load testing of structures
 Corroscan/C-scan
 3D Computed Tomography
 Industrial CT Scanning
 Heat Exchanger Life Assessment System
 RTJ Flange Special Ultrasonic Testing
3.1. VISUAL INSPECTION and OPTICAL
MICROSCOPY METHOD
The visual inspection is the most basic method of the non destructive testing. It
can be done by the naked human eyes. It is fast and economic and can be used
to check only the surface irregularities or fractures. But it has got its own
disadvantages like it is not much accurate in terms of dimensions and hence it is
not reliable. Also it can be used only within the range of vision of human eyes
so very fine inspection cannot be done by this method.

8. 8
Optical microscopy is and modified version of the visual inspection method as it
counters for few of the limitation of the prior method. It makes use of the
optical microscopes with high magnification powers for inspection. It is also
cheap and easy. But, also it cannot go beyond the inspection of only the surface
properties.
3.2. DYE PENETRATION TEST
Dye penetrant inspection (DPI), also called liquid penetrant
inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost
inspection method used to locate surface-breaking defects in all non-
porous materials (metals, plastics, or ceramics). The penetrant may be applied to
all non-ferrous materials and ferrous materials, although for ferrous
components magnetic-particle inspection is often used instead for its subsurface
detection capability. LPI is used to detect casting, forging and welding surface
defects such as hairline cracks, surface porosity, leaks in new products,
and fatigue cracks on in-service components.
PRINCIPLE
DPI is based upon capillary action, where low surface tension fluid penetrates
into clean and dry surface-breaking discontinuities. Penetrant may be applied to
the test component by dipping, spraying, or brushing. After adequate
penetration time has been allowed, the excess penetrant is removed and a
developer is applied. The developer helps to draw penetrant out of the flaw so
that an invisible indication becomes visible to the inspector. Inspection is
performed under ultraviolet or white light, depending on the type of dye used -
fluorescent or nonfluorescent (visible).
STEPS of INSPECTION
1. Pre-cleaning:
The test surface is cleaned to remove any dirt, paint, oil, grease or any loose
scale that could either keep penetrant out of a defect, or cause irrelevant or false
indications. Cleaning methods may include solvents, alkaline cleaning
steps, vapor degreasing, or media blasting. The end goal of this step is a clean
surface where any defects present are open to the surface, dry, and free of
contamination. Note that if media blasting is used, it may "work over" small
discontinuities in the part, and an etching bath is recommended as a post-
blasting treatment.

9. 9
2. Application of Penetrant:
The penetrant is then applied to the surface of the item being tested. The
penetrant is allowed "dwell time" to soak into any flaws (generally 5 to 30
minutes). The dwell time mainly depends upon the penetrant being used,
material being tested and the size of flaws sought. As expected, smaller flaws
require a longer penetration time. Due to their incompatible nature one must be
careful not to apply solvent-based penetrant to a surface which is to be
inspected with a water-washable penetrant.
3. Excess Penetrant Removal:
The excess penetrant is then removed from the surface. The removal method is
controlled by the type of penetrant used. Water-washable, solvent-
removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the
common choices. Emulsifiersrepresent the highest sensitivity level, and
chemically interact with the oily penetrant to make it removable with a water
spray. When using solvent remover and lint-free cloth it is important to not
spray the solvent on the test surface directly, because this can remove the
penetrant from the flaws. If excess penetrant is not properly removed, once the
developer is applied, it may leave a background in the developed area that can

10. 10
mask indications or defects. In addition, this may also produce false indications
severely hindering your ability to do a proper inspection. Also, the removal of
excessive penetrant is done towards one direction either vertically or
horizontally as the case may be.
4. Application of Developer:
After excess penetrant has been removed, a white developer is applied to the
sample. Several developer types are available, including: non-aqueous wet
developer, dry powder, water-suspendable, and water-soluble. Choice of
developer is governed by penetrant compatibility (one can't use water-soluble or
-suspendable developer with water-washable penetrant), and by inspection
conditions. When using non-aqueous wet developer (NAWD) or dry powder,
the sample must be dried prior to application, while soluble and suspendable
developers are applied with the part still wet from the previous step. NAWD is
commercially available in aerosol spray cans, and may
employ acetone, isopropyl alcohol, or a propellant that is a combination of the
two. Developer should form a semi-transparent, even coating on the surface.
The developer draws penetrant from defects out onto the surface to form a
visible indication, commonly known as bleed-out. Any areas that bleed out can
indicate the location, orientation and possible types of defects on the surface.
Interpreting the results and characterizing defects from the indications found
may require some training and/or experience [the indication size is not the
actual size of the defect].
5. Inspection:
The inspector will use visible light with adequate intensity (100 foot-candles or
1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of
adequate intensity (1,000 micro-watts per centimeter squared is common), along
with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant
examinations. Inspection of the test surface should take place after 10- to 30-
minute development time, depends of product kind. This time delay allows the
blotting action to occur. The inspector may observe the sample for indication
formation when using visible dye. It is also good practice to observe indications
as they form because the characteristics of the bleed out are a significant part of
interpretation characterization of flaws.
6. Post Cleaning:
The test surface is often cleaned after inspection and recording of defects,
especially if post-inspection coating processes are scheduled.
ADVANTAGES AND DISADVANTAGES
The main advantages of DPI are the speed of the test and the low cost.
Disadvantages include the detection of only surface flaws, skin irritation, and

11. 11
the inspection should be on a smooth clean surface where excessive penetrant
can be removed prior to being developed. Conducting the test on rough
surfaces, such-as "as-welded" welds, will make it difficult to remove any
excessive penetrant and could result in false indications. Water-washable
penetrant should be considered here if no other option is available. Also, on
certain surfaces a great enough color contrast cannot be achieved or the dye will
stain the workpiece.[1]
Limited training is required for the operator — although experience is quite
valuable. Proper cleaning is necessary to assure that surface contaminants have
been removed and any defects present are clean and dry. Some cleaning
methods have been shown to be detrimental to test sensitivity, so acid etching to
remove metal smearing and re-open the defect may be necessary.
3.3. MAGNETIC PARTICLE INSPECTION
Magnetic particle Inspection (MPI) is a non-destructive testing (NDT)
process for detecting surface and slightly subsurface discontinuities
in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys.
The process puts a magnetic field into the part. The piece can be magnetized by
direct or indirect magnetization. Direct magnetization occurs when the electric
current is passed through the test object and a magnetic field is formed in the
material. Indirect magnetization occurs when no electric current is passed
through the test object, but a magnetic field is applied from an outside source.
The magnetic lines of force are perpendicular to the direction of the electric
current, which may be either alternating current (AC) or some form of direct
current (DC) (rectified AC).
The presence of a surface or subsurface discontinuity in the material allows
the magnetic flux to leak, since air cannot support as much magnetic field per
unit volume as metals. Ferrous particles are then applied to the part. The
particles may be dry or in a wet suspension. If an area of flux leakage is present,
the particles will be attracted to this area. The particles will build up at the area

12. 12
of leakage and form what is known as an indication. The indication can then be
evaluated to determine what it is, what may have caused it, and what action
should be taken, if any.
TYPES OF CURRENT USED
There are several types of electrical currents used in magnetic particle
inspection. For a proper current to be selected one needs to consider the part
geometry, material, the type of discontinuity one is seeking, and how far the
magnetic field needs to penetrate into the part.
 Alternating current (AC) is commonly used to detect surface
discontinuities. Using AC to detect subsurface discontinuities is limited due
to what is known as the skin effect, where the current runs along the surface
of the part. Because the current alternates in polarity at 50 to 60 cycles per
second it does not penetrate much past the surface of the test object. This
means the magnetic domains will only be aligned equal to the distance AC
current penetration into the part. The frequency of the alternating current
determines how deep the penetration.
 Full wave DC (FWDC) is used to detect subsurface discontinuities where
AC can not penetrate deep enough to magnetize the part at the depth needed.
The amount of magnetic penetration depends on the amount of current
through the part.[1]
DC is also limited on very large cross-sectional parts in
terms of how effectively it will magnetize the part.
 Half wave DC (HWDC, pulsating DC) works similar to full wave DC, but
allows for detection of surface breaking indications and has more magnetic
penetration into the part than FWDC. HWDC is advantageous for inspection
process as it actually helps move the magnetic particles during the bathing of
the test object. The aid in particle mobility is caused by the half-wave
pulsating current waveform. In a typical mag pulse of 0.5 seconds there are
15 pulses of current using HWDC. This gives the particle more of an
opportunity to come in contact with areas of magnetic flux leakage.
Each method of magnetizing has its pros and cons. AC is generally the best for
discontinuities on the surface, while some form of DC is better for subsurface
defects.
EQUIPMENTS
 A wet horizontal MPI machine is the most commonly used mass-production
inspection machine. The machine has a head and tail stock where the part is
placed to magnetize it. In between the head and tail stock is typically an
induction coil, which is used to change the orientation of the magnetic field
by 90° from the head stock. Most of the equipment is built for a specific
application.

13. 13
 Mobile power packs are custom-built magnetizing power supplies used in
wire wrapping applications.
 Magnetic yoke is a hand-held device that induces a magnetic field between
two poles. Common applications are for outdoor use, remote locations,
and weld inspection. The draw back of magnetic yokes is that they only
induce a magnetic field between the poles, so large-scale inspections using
the device can be time-consuming. For proper inspection the yoke needs to
be rotated 90 degrees for every inspection area to detect horizontal and
vertical discontinuities. Subsurface detection using a yoke is limited. These
systems used dry magnetic powders, wet powders, or aerosols.
MAGNETIC PARTICLES POWDER
A common particle used to detect cracks is iron oxide, for both dry and wet
systems.
 Wet system particle range in size from less than 0.5 micrometres to 10
micrometres for use with water or oil carriers. Particles used in wet systems
have pigments applied that fluoresce at 365 nm (ultraviolet A) requiring
1000 µW/cm2
(10 W/m2
) at the surface of the part for proper inspection. If
the particles do not have the correct light applied in a darkroom the particles
cannot be detected/seen. It is industry practice to use UV goggles/glasses to
filter the UV light and amplify the visible light spectrum (normally green
and yellow) created by the fluorescing particles. Green and yellow
fluorescence was chosen, because the human eye reacts best to these colors.
 Dry particle powders range in size from 5 to 170 micrometres, designed to
be seen in white light conditions. The particles are not designed to be used in
wet environments. Dry powders are normally applied using hand operated
air powder applicators.
 Aerosol applied particles are similar to wet systems, sold in premixed
aerosol cans similar to hair spray.
STEPS
The following are general steps for inspecting on a wet horizontal machine:
1. Part is cleaned of oil and other contaminants.
2. Necessary calculations done to know the amount of current required to
magnetize the part. Refer ASTM E1444/E1444M for formulas.
3. The magnetizing pulse is applied for 0.5 seconds, during which the
operator washes the part with the particle, stopping before the magnetic
pulse is completed. Failure to stop prior to end of the magnetic pulse will
wash away indications.

14. 14
4. UV light is applied while the operator looks for indications of defects that
are 0 to ±45 degrees from path the current flowed through the part.
Indications only appear 45 to 90 degrees of the magnetic field applied.
The easiest way to quickly figure out which way the magnetic field is
running is grab the part with either hand between the head stocks laying
your thumb against the part (do not wrap your thumb around the part)
this is called either left or right thumb rule or right hand grip rule. The
direction the thumb points tell us the direction current is flowing, the
magnetic field will be running 90 degrees from the current path. On
complex geometry, like a crankshaft, the operator needs to visualize the
changing direction of the current and magnetic field created. The current
starts at 0 degrees then 45 degrees to 90 degree back to 45 degrees to 0
then -45 to -90 to -45 to 0 and this is repeated for each crankpin. Thus, it
can be time consuming to find indications that are only 45 to 90 degrees
from the magnetic field.
5. The part is either accepted or rejected, based on pre-defined criteria.
6. The part is demagnetized.
7. Depending on requirements, the orientation of the magnetic field may
need to be changed 90 degrees to inspect for indications that cannot be
detected from steps 3 to 5. The most common way to change magnetic
field orientation is to use a "coil shot". In Fig 1 a 36 inch coil can be seen
then steps 4, 5, and 6 are repeated.
3.4. ULTRASONIC TESTING
Ultrasonic testing (UT) is a family of non-destructive testing techniques based
on the propagation of ultrasonic waves in the object or material tested. In most
common UT applications, very short ultrasonic pulse-waves with center
frequencies ranging from 0.1-15 MHz, and occasionally up to 50 MHz, are
transmitted into materials to detect internal flaws or to characterize materials. A
common example is ultrasonic thickness measurement, which tests the thickness
of the test object, for example, to monitor pipework corrosion.
Ultrasonic testing is often performed on steel and other metals and alloys,
though it can also be used on concrete, wood and composites, albeit with less
resolution. It is used in many industries including steel and aluminium
construction, metallurgy, manufacturing, aerospace, automotive and
other transportation sectors.

15. 15
WORKING
In ultrasonic testing, an ultrasound transducer connected to a diagnostic
machine is passed over the object being inspected. The transducer is typically
separated from the test object by a couplant (such as oil) or by water, as in
immersion testing. However, when ultrasonic testing is conducted with
an Electromagnetic Acoustic Transducer (EMAT) the use of couplant is not
required.
There are two methods of receiving the ultrasound waveform: reflection and
attenuation. In reflection (or pulse-echo) mode, the transducer performs both the
sending and the receiving of the pulsed waves as the "sound" is reflected back
to the device. Reflected ultrasound comes from an interface, such as the back
wall of the object or from an imperfection within the object. The diagnostic
machine displays these results in the form of a signal with
an amplitude representing the intensity of the reflection and the distance,
representing the arrival time of the reflection. In attenuation (or through-
transmission) mode, a transmitter sends ultrasound through one surface, and a
separate receiver detects the amount that has reached it on another surface after
traveling through the medium. Imperfections or other conditions in the space
between the transmitter and receiver reduce the amount of sound transmitted,
thus revealing their presence. Using the couplant increases the efficiency of the
process by reducing the losses in the ultrasonic wave energy due to separation
between the surfaces.

16. 16
Advantages
1. High penetrating power, which allows the detection of flaws deep in the
part.
2. High sensitivity, permitting the detection of extremely small flaws.
3. In many cases only one surface needs to be accessible.
4. Greater accuracy than other non-destructive methods in determining the
depth of internal flaws and the thickness of parts with parallel surfaces.
5. Some capability of estimating the size, orientation, shape and nature of
defects.
6. Some capability of estimating the structure of alloys of components with
different acoustic properties
7. Non-hazardous to operations or to nearby personnel and has no effect on
equipment and materials in the vicinity.
8. Capable of portable or highly automated operation.
9. Results are immediate. Hence on the spot decisions can be made.
Disadvantages[edit]
1. Manual operation requires careful attention by experienced technicians.
The transducers alert to both normal structure of some materials,
tolerable anomalies of other specimens (both termed “noise”) and to
faults therein severe enough to compromise specimen integrity. These
signals must be distinguished by a skilled technician, possibly requiring
follow up with other nondestructive testing methods.[1]
2. Extensive technical knowledge is required for the development of
inspection procedures.
3. Parts that are rough, irregular in shape, very small or thin, or not
homogeneous are difficult to inspect.
4. Surface must be prepared by cleaning and removing loose scale, paint,
etc., although paint that is properly bonded to a surface need not be
removed.
5. Couplants are needed to provide effective transfer of ultrasonic wave
energy between transducers and parts being inspected unless a non-
contact technique is used. Non-contact techniques include Laser and
Electro Magnetic Acoustic Transducers (EMAT).
6. Inspected items must be water resistant, when using water based
couplants that do not contain rust inhibitors.

17. 17
3.5. RADIOGRAPHIC TESTING
Radiographic Testing (RT), or industrial radiography, is a non-
destructive testing method of inspecting materials for hidden flaws by using the
ability of short wavelength electromagnetic radiation (high energy photons) to
penetrate various materials.
Working
In Radiography Testing the test-part is placed between the radiation source and
film (or detector). The material density and thickness differences of the test-part
will attenuate (i.e. reduce) the penetrating radiation through interaction
processes involving scattering and/or absorption. The differences in absorption
are then recorded on film(s) or through an electronic means. In industrial
radiography there are several imaging methods available, techniques to display
the final image, i.e. Film Radiography, Real Time Radiography (RTR),
Computed Tomography (CT), Digital Radiography (DR), and Computed
Radiography (CR).
There are two different radioactive sources available for industrial use; X-ray
and Gamma-ray. These radiation sources use higher energy level, i.e. shorter
wavelength, versions of the electromagnetic waves. Because of the radioactivity
involved in radiography testing, it is of paramount importance to ensure that the
Local Rules is strictly adhered during operation.
Industrial Radiography inspection is used to detect features of a component or
assembly that exhibit a difference in thickness or physical density as compared
to surrounding material. Large differences are more easily detected than small
ones. In general, radiography can detect only those features that have an
appreciable thickness in direction parallel to the radiation beam. This means that

18. 18
the ability of the process to detect planar discontinuities such as cracks depends
on proper orientation of the test piece during testing. Discontinuities such as
voids and inclusions, which have measurable thickness in all directions, can be
detected as long as they are not too small in relation to section thickness. In
general, features that exhibit a 2% or more difference in absorption compared to
the surrounding material can be detected. Radiography is more effective when
the flaws are not planar.
Advantages
 Can inspect assembled components
 Minimum surface preparation required
 Detects both surface and subsurface defects
 Provides a permanent record of the inspection
 Verify internal flaws on complex structures
 Isolate and inspect internal components
 Automatically detect and measure internal flaws
 Measure dimensions and angles within the sample without sectioning
 Sensitive to changes in thickness, corrosion, flaws and material density
changes
Applications
 Aerospace industries
 Military defence
 Offshore industries
 Marine industries
 Power-gen industries
 Petrochem industries
 Waste Management
 Automotive industries
 Manufacturing industries
 Transport industries

19. 19
4. APPLICATIONS OF NDT
NDT is used in a variety of settings that covers a wide range of industrial
activity, with new NDT methods and applications, being continuously
developed. Non-destructive testing methods are routinely applied in industries
where a failure of a component would cause significant hazard or economic
loss, such as in transportation, pressure vessels, building structures, piping, and
hoisting equipment.
The field of area where NDT is used are forensic engineering, mechanical
engineering, petroleum engineering, electrical engineering, civil
engineering, systems engineering, aeronautical engineering, medicine,
and art.[1]
Innovations in the field of non-destructive testing have had a profound
impact on medical imaging, including on echocardiography, medical
ultrasonography, and digital radiography.

20. 20
5. ADVANTAGES OF NDT
1. Safety
Non-destructive testing is conducted to determine whether a component is
compromised or in need of repair. The tests are designed to maximize both
tester and tested product safety. In other words, most tests are completely
harmless to humans (radiographic testing must be conducted under strict
settings), and all tests leave tested products completely undamaged.
2. Reliability
When it comes to accurate results, non-destructive testing is reliable because of
the variety of available and complementary options. Any given piece of
equipment or machinery can be subject to a number of non-destructive tests,
which eliminates the risk of oversight or inaccuracy.
3. Test particles can be used
In NDT, the test particles are not damaged and hence they can be used again.
4. Affordability
Different industries have different safety standards, and different types of
machinery have to be regularly inspected at different intervals. But regardless of
what has to be inspected, a non-destructive test will always be the most
affordable option. Destructive testing methods (like automobile crash tests)
typically cost an order of higher magnitude.
5. Peace of Mind
The final benefit of non-destructive testing may be hard to quantify, but it’s the
most important of all. Knowing that your equipment is functioning the way it
should (and that future accidents can be prevented with simple checkups) adds
years to the life of a beleaguered project manager. And when workers know
they’re safe, work productivity goes up all around.

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6. DISADVANTAGES OF NDT
1. It requires a higher level of training and additional certification
2. Comparatively complicated operations
3. High-value advanced instrumentation is needed.
4. High capital and maintenance required

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7. CONCLUSIONS
On the basis of above discussion we can say that Non Destructive Testing 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, which uses many non conventional principles to perform its function.
Few such examples may be use of electromagnetic radiation, sound, and
inherent properties of materials for testing.
Also there are wide range of types of NDT depending upon the pprinciple used
such as radiographic testing, ultrasonic testing etc.
Like every other thing in universe, NDT also has some advantages and
disadvantages. Advantages like reliability, accuracy, precision, fast operations
are also accompanied by disadvantages like need of training, high maintenance,
high capital costs etc.
On a whole, we can say that NDT is a revolutionary advancement in field of
mechanical testing. And on the basis of its scope and increasing areas of
application we can say that many more new advancements in NDT are yet to
come.

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8. REFERENCES
www.ndt-ed.org
www.google.com
www.insidendt.com
www.wikipedia.com
www.twi-global.com