2. Outline
What is NDT ?
Where is NDT used ?
When is NDT used ?
Types of Discontinuities.
Common NDT methods.
3. What is NDT ? Contd..
The field of Nondestructive Testing (NDT) is a very
broad field that plays a critical role in assuring that
structural components and systems perform their
function in a reliable and cost effective fashion. NDT
technicians and engineers define and implement
tests that locate and characterize material conditions
and flaws that might otherwise cause planes to
crash, reactors to fail, trains to derail, pipelines to
burst, and a variety of less visible, but equally
troubling events.
4. What is NDT ? Contd..
Because NDT allows inspection without interfering
with a product's final use, it provides an excellent
balance between quality control and cost-
effectiveness. Technology that is used in NDT is
similar to those used in the medical industry; yet,
typically nonliving objects are the subjects of the
inspections.
5. Where is NDT used ?
NDT is used where we need to ensure the
serviceability of a specimen. That may be the use of a
raw material such as a casting, the use of fabrication
such as welding, or the use of a finished part or
completed system. We apply NDT where we cannot
afford the cost of a failure of the specimen because
failure would be financially unacceptable or cause
harm to us.
6. When is NDT used ?
NDT is used both before and after production of
raw materials such as ingots and castings,
before and after fabrication, and before and
after assembly of parts into a completed
system. Using NDT "before" prevents a
substandard material or part from wasting time
and increasing scrap production. The "when" is
right if profit, quality, and safety are the result of
using NDT.
7. Discontinuities
Definition : The change in the geometry or
composition of an object either intentional or
unintentional.
Such changes inherently affect the physical
properties of the object and have an effect on the
objects ability to fulfill its intended use or service life.
Every discontinuity is not a defect but every
defect is a discontinuity.
8. Discontinuities Contd…
The definition of defects changes with the type of
component, its construction, its materials and the
specifications or codes in force.
It is possible that discontinuity in one object may be
defect in another. Detection of discontinuities is
largely dependent on the discontinuity’s physical
characteristics.
9. Discontinuities Contd…
While performing NDT it is also important to consider
how the material is produced, what manufacturing
process are used to form the finished product and
what discontinuities are typically initiated by the
process operations. Discontinuity is categorized by
the stage of manufacturing or use in which it
initiates.
10. Discontinuities Contd…
Discontinuity is categorized in four stages
Inherent discontinuities.
Primary processing discontinuities.
Secondary processing discontinuities.
Service induced discontinuities.
11. Common NDT Methods
The most common NDT methods used are as
follows :
Penetrant Testing.
Magnetic Particle Testing.
Ultrasonic Testing.
Radiography Testing.
12. Penetrant Testing
Penetrant solution is applied to
the surface of a precleaned
component. The liquid is pulled
into surface-breaking defects
by capillary action. Excess
penetrant material is carefully
cleaned from the surface. A
developer is applied to pull the
trapped penetrant back to the
surface where it is spread out
and forms an indication. The
indication is much easier to see
than the actual defect.
13. Steps of Penetrant Testing
1. Surface Preparation: One of the most critical
steps of a liquid penetrant inspection is the
surface preparation. The surface must be free of
oil, grease, water, or other contaminants that may
prevent penetrant from entering flaws. The
sample may also require etching if mechanical
operations such as machining, sanding, or grit
blasting have been performed. These and other
mechanical operations can smear the surface of
the sample, thus closing the defects.
14. Steps of Penetrant Testing
2. Penetrant Application: Once the surface has been thoroughly
cleaned and dried, the penetrant material is applied by
spraying, brushing, or immersing the parts in a penetrant
bath.
15. Steps of Penetrant Testing
3. Penetrant Dwell: The penetrant is left on the surface for a
sufficient time to allow as much penetrant as possible to be
drawn from or to seep into a defect. Penetrant dwell time is
the total time that the penetrant is in contact with the part
surface. Dwell times are usually recommended by the
penetrant producers or required by the specification being
followed. Minimum dwell times typically range from 5 to 60
minutes. Generally, there is no harm in using a longer
penetrant dwell time as long as the penetrant is not allowed
to dry. The ideal dwell time is often determined by
experimentation and is often very specific to a particular
application.
16. Steps of Penetrant Testing
4. Excess Penetrant Removal: This is a most delicate
part of the inspection procedure because the excess
penetrant must be removed from the surface of the
sample while removing as little penetrant as
possible from defects. Depending on the penetrant
system used, this step may involve cleaning with a
solvent, direct rinsing with water, or first treated with
an emulsifier and then rinsing with water .
18. Steps of Penetrant Testing
5. Developer Application: A thin layer of developer is
then applied to the sample to draw penetrant
trapped in flaws back to the surface where it will be
visible. Developers come in a variety of forms that
may be applied by dusting (dry powdered), dipping,
or spraying (wet developers).
19. Steps of Penetrant Testing
6. Indication Development: The developer is allowed to
stand on the part surface for a period of time sufficient
to permit the extraction of the trapped penetrant out of
any surface flaws. This development time is usually a
minimum of 10 minutes and significantly longer times
may be necessary for tight cracks.
20. Steps of Penetrant Testing
7. Inspection: Inspection is then performed under
appropriate lighting to detect indications from any
flaws which may be present.
8. Clean Surface: The final step in the process is to
thoroughly clean the part surface to remove the
developer from the parts that were found to be
acceptable.
21. Main uses of Penetrant Testing
Used to locate cracks, porosity, and other defects
that break the surface of a material and have enough
volume to trap and hold the penetrant material.
Liquid penetrant testing is used to inspect large
areas very efficiently and will work on most
nonporous materials.
22. Advantages of Penetrant Testing
Large surface areas or large volumes of
parts/materials can be inspected rapidly and at low
cost.
Parts with complex geometry are routinely inspected.
Indications are produced directly on surface of the
part providing a visual image of the discontinuity.
Equipment investment is minimal.
Due to portability it is suitable for remote areas.
23. Disadvantages of Penetrant Testing
Detects only surface breaking defects.
Surface preparation is critical as contaminants can
mask defects.
Requires a relatively smooth and nonporous surface.
Post cleaning is necessary to remove chemicals.
Requires multiple operations under controlled
conditions.
Chemical handling precautions are necessary (toxicity,
fire, waste).
24. Magnetic Particle Testing
This NDT method is accomplished by inducing a
magnetic field in a ferromagnetic material and then
dusting the surface with iron particles (either dry or
suspended in liquid). Surface and near-surface flaws
produce magnetic poles or distort the magnetic field
in such a way that the iron particles are attracted and
concentrated. This produces a visible indication of
defect on the surface of the material.
26. Magnetization
1. Longitudinal Magnetization : When the length of a
component is several time larger than its diameter, a
longitudinal magnetic field can be established in the
component. The component is often placed
longitudinally in the concentrated magnetic field that
fills the center of a coil or solenoid. This
magnetization technique is often referred to as a
"coil shot."
28. Magnetization
2. Circular Magnetization : when current is passed
through a solid conductor, a magnetic field forms in
and around the conductor.
The field strength varies from zero at the center of
the component to a maximum at the surface.
32. Before and after inspection pictures of cracks
emanating from a hole
Examples of Magnetic Particle Indication
33. Indication of a crack in a saw blade
Examples of Magnetic Particle Indication
34. Indication of cracks running between
attachment holes in a hinge
Examples of Magnetic Particle Indication
35. Indication of cracks originating at a
fastener hole
Examples of Magnetic Particle Indication
36. Magnetic particle wet fluorescent indication
of a cracks in a drive shaft
Examples of Magnetic Particle Indication
37. Magnetic particle wet fluorescent indication of
a crack in a bearing
Examples of Magnetic Particle Indication
38. Main uses of MT
Used to inspect ferromagnetic materials (those that
can be magnetized) for finding defects. Magnetic
particle inspection can detect surface and near
surface defects.
39. Advantages of MT
Large surface areas of complex parts can be
inspected rapidly.
Can detect surface and subsurface flaws.
Surface preparation is less critical than in
penetrant testing.
Magnetic particle indications are produced
directly on the surface of the part and form an
image of the discontinuity.
Equipment costs are relatively low.
40. Disadvantages of MT
Only ferromagnetic materials can be inspected.
Large currents are needed for very large parts.
Requires relatively smooth surface.
Paint or other nonmagnetic coverings adversely
affect sensitivity.
Demagnetization and post cleaning is usually
necessary.
41. High frequency sound waves are introduced into a
material and they are reflected back from surfaces or
flaws.
Reflected sound energy is displayed versus time, and
inspector can visualize a cross section of the specimen
showing the depth of features that reflect sound.
f
plate
crack
0 2 4 6 8 10
initial
pulse
crack
echo
back surface
echo
Oscilloscope, or flaw
detector screen
Ultrasonic Testing
42. f
Ultrasonic Testing
A typical UT inspection system consists of several
functional units, such as the pulsar/receiver,
transducer, and display devices. A pulsar/receiver is
an electronic device that can produce high voltage
electrical pulse. Driven by the pulsar, 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.
43. f
Ultrasonic Testing
The reflected wave signal is transformed into
electrical signal by the transducer and is displayed
on a screen. The reflected signal strength is
displayed versus the time from signal generation to
when a echo was received. Signal travel time can
be directly related to the distance that the signal
traveled. From the signal, information about the
reflector location, size, orientation and other
features can sometimes be gained.
45. Types Of Sound Waves & Propagation
In solids, molecules can support vibrations in other
directions so the number of different types (modes)
of sound waves are possible. On the basis of particle
displacement in the medium ultrasonic waves are
classified as longitudinal waves , transverse waves ,
surface waves and lamb waves . Velocity remains
the same in the given medium.
46. Types Of Sound Waves & Propagation
There are four types of sound waves :
Longitudinal - Parallel to wave direction
Transverse - Perpendicular to wave direction
Surface (Rayleigh) - Elliptical orbit symmetrical mode
Plate Wave (Lamb) - Component perpendicular to
surface (extensional wave)
47. Types Of Sound Waves & Propagation
Longitudinal or Compressional Wave
These waves mostly used in the inspection of
materials.The velocity of longitudinal waves is about
6000 m/sec in steel,1500 m/sec in water and 330
m/sec in air.
Longitudinal waves have particle vibration in a back
and forth motion in the direction of wave
propagation. These waves are readily propagated in
the liquids,gases and elastic solids.
49. Types Of Sound Waves & Propagation
Transverse or Shear Wave
These wave have particle vibration perpendicular to
the direction of wave motion.These waves will not
travel through liquid, gases because force of
attraction between molecules are too small . the
velocity of these waves is about 50% the longitudinal
waves for the same medium.
51. Types Of Sound Waves & Propagation
Surface or Reyleigh Wave
These waves travel along the flat or curved surface
of relatively thick solid parts.The velocity of these
waves are 90% of the transverse waves in the same
material. Surface waves are useful for detecting
surface cracks.Vibration of particle follow an elliptical
path.
53. Types Of Sound Waves & Propagation
Plate or Lamb Wave
These waves also another type of ultrasonic waves
used to detect surface defect and penetrates only
upto half of wave length.These waves propagate in
thin plate or sheet only.
54. Transducer or Probe in UT
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. The active element is the heart of
the transducer as it converts the electrical energy to
acoustic energy, and vice versa.
55. Transducer or Probe in UT
Transducers or probes are very important tool in the
system. They act through couplant.The sensitivity of
a transducer is defined as its ability to detect
smallest discontinuities and it is measured by the
response of reflection from artificial discontinuity in
reference
56. Couplant
A couplant is a material (usually liquid) that facilitates
the transmission of ultrasonic energy from the
transducer into the test specimen. Couplant is
generally necessary because the acoustic
impedance mismatch between air and solids, such
as the test specimen, is large and, therefore, nearly
all of the energy is reflected and very little is
transmitted into the test material.
57. Couplant
The couplant displaces the air and makes it possible
to get more sound energy into the test specimen so
that a usable ultrasonic signal can be obtained. In
contact ultrasonic testing a thin film of oil, glycerin or
water is generally used and in immersion testing
water is between the transducer and the test
surface.
58. Main uses of UT
Used to locate surface and subsurface defects in
materials. Ultrasonic inspection is also used to
measure the thickness of materials.
59. Advantages of UT
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 reflector position and estimating
size and shape.
Minimal part preparation required.
Electronic equipment provides immediate results.
Detailed images can be produced with automated systems.
It has other uses such as thickness measurements, in addition to
flaw detection.
60. Disadvantages of UT
Surface must be accessible to transmit ultrasound.
Skill and training is more extensive than with some other methods.
It normally requires a coupling medium for transfer of sound energy into
test specimen.
Materials that are rough, irregular in shape, very small, exceptionally
thin or not homogeneous are difficult to inspect.
Cast iron and other coarse grained materials are difficult to inspect due
to low sound transmission and high signal noise.
Linear defects oriented parallel to the sound beam may go undetected.
Reference standards are required for both equipment calibration, and
characterization of flaws.
61. The radiation used in radiography testing is a higher
energy (shorter wavelength) electromagnetic waves.
The radiation came from an X-ray generator or a
radioactive source.
Radiography Testing
63. Radiography Testing
RT involves the use of penetrating gamma- or X-
radiation to examine material's and product's defects
and internal features. An X-ray machine or
radioactive isotope is used as a source of radiation.
Radiation is directed through a part on film. The
resulting shadowgraph shows the internal features
and soundness of the part. Material thickness and
density changes are indicated as lighter or darker
areas on the film.
64. Top view of developed film
X-ray film
X-rays are used to produce
images of objects using film or
other detector that is sensitive
to radiation. The test object is
placed between the radiation
source and detector. The
thickness and the density of
the material in which X-rays
penetrate affects the amount
of radiation reaching the
detector.
Radiography Testing
65. Radiography Testing
This variation in radiation produces an image on the
detector that often shows internal features of the test
object.The part is placed between the radiation
source and a piece of film. The part will stop some
of the radiation. Thicker and more dense area will
stop more of the radiation.
66. Main Uses of RT
Used to inspect almost any material for surface and
subsurface defects. X-rays can also be used to
locates and measures internal features, confirm the
location of hidden parts in an assembly.
67. Advantages of RT
Can be used to inspect virtually all materials.
Detects surface and subsurface defects.
Ability to inspect complex shapes and multi-layered
structures without disassembly.
Minimum part preparation is required.
68. Disadvantages of RT
Extensive operator training and skill required.
Access to both sides of the structure is usually
required.
Orientation of the radiation beam to non-volumetric
defects is critical.
Relatively expensive equipment investment is
required.
Possible radiation hazard for personnel.
69. Non-Destructive Testing Method & Application
Material
Flaw type
Surface
Cracks
&
Flaws
Sub-
Surfa
ce
Crack
s &
Flaws
Internal
Flaws
&
Discont
inuities
Lack
of
bond
Or
lack of
Fusio
n
Non-
Metallic
Inclusions-
Slag,
porosity
Material
Quality
Laminations
,
Thickness
Measureme
nt
Ferrous
welds
M.T.
U.T.
P.T.
U.T.
R.T.
U.T.
R.T.
U.T.
R.T.
U.T.
U.T.
Steel
castings
M.T.
M.T.
U.T.
R.T.
U.T.
R.T.
U.T.
U.T.
Iron castings M.T.
U.T.
E.T.
U.T.
R.T.
U.T.
U.T. U.T.
Non-Ferrous
Components
&
Materials
P.T.
R.T.
U.T.
U.T.
P.T.
U.T.
U.T.
