This document provides an overview of non-destructive testing (NDT) techniques. It discusses the six most common NDT methods: visual inspection, liquid penetrant testing, magnetic particle inspection, ultrasonic testing, eddy current testing, and radiography. For each method, it describes the basic principles, applications, advantages, and limitations. The document is intended as an introduction to NDT methods for students studying airframe maintenance and repair. It concludes with review questions to test understanding of key concepts.

1. AE6010-AIRFRAME MAINTENANCE
AND REPAIR
UNIT-I-NDT TECHNIQUES
B.DEEBAN ME(PhD)
ASSISTANT PROFESSOR
KIT-KALAIGNARKARUNANIDHI INSTITUTE OF
TECHNOLOGY(AUTONOMOUS)
COIMBATORE

2. Non-destructive Analysis (NDA)
Non-destructive Testing (NDT)
https://www.nde-ed.org/index_flash.php
 Introduction to NDT
 Overview of Six Most Common NDT Methods
 Selected Applications
https://www.youtube.com/watch?v=tlE3eK0g6vU NDT very good

3. The use of noninvasive
techniques to determine
the integrity of a material,
component or structure
or
quantitatively measure
some characteristic of
an object.
i.e. Inspect or measure without doing harm.
Definition of NDT

4. What are Some Uses
of NDT Methods?
• Flaw Detection and Evaluation
• Leak Detection
• Location Determination
• Dimensional Measurements
• Structure and Microstructure Characterization
• Estimation of Mechanical and Physical Properties
• Material Sorting and Chemical Composition
Determination
Fluorescent penetrant indication

5. Why Nondestructive?
• Test piece too precious to be destroyed
• Test piece to be reused after inspection
• Test piece is in service
• For quality control purpose
• Something you simply cannot do harm
to, e.g. fetus in mother’s uterus

6. When are NDE Methods Used?
–To assist in product development
–To screen or sort incoming materials
–To monitor, improve or control
manufacturing processes
–To verify proper processing such as
heat treating
–To verify proper assembly
–To inspect for in-service damage
There are NDE applications at almost any stage
in the production or life cycle of a component.

7. Six Most Common NDT Methods
• Visual
• Liquid Penetrant
• Magnetic
• Ultrasonic
• Eddy Current
• Radiography
Detection of surface flaws
Detection of internal flaws

8. Most basic and common
inspection method.
Tools include
fiberscopes,
borescopes, magnifying
glasses and mirrors.
Robotic crawlers permit
observation in hazardous or
tight areas, such as air
ducts, reactors, pipelines.
Portable video inspection
unit with zoom allows
inspection of large tanks
and vessels, railroad tank
cars, sewer lines.
1. Visual Inspection

9. https://www.youtube.com/watch?v=tlE3eK0g6vU at~2:48-3:33 https://www.youtube.com/watch?v=bHTRmTQDZzg
• A liquid with high surface wetting characteristics
is applied to the surface of the part and allowed
time to seep into surface breaking defects.
• The excess liquid is removed from the surface
of the part.
• A developer (powder) is applied to pull the
trapped penetrant out the defect and spread it
on the surface where it can be seen.
• Visual inspection is the final step in the
process. The penetrant used is often loaded
with a fluorescent dye and the inspection is
done under UV light to increase test
sensitivity.
Liquid Penetrant Inspection
High surface wetting
Low surface wetting
https://www.youtube.com/watch?v=xEK-c1pkTUI to~2:26

10. • A NDT method used for defect detection. Fast and relatively
easy to apply and part surface preparation is not as critical as
for some other NDT methods. – MPI one of the most widely
utilized nondestructive testing methods.
• MPI uses magnetic fields and small magnetic particles, such
as iron filings to detect flaws in components. The only
requirement from an inspectability standpoint is that the
component being inspected must be made of a
ferromagnetic material such as iron, nickel, cobalt, or
some of their alloys. Ferromagnetic materials are materials
that can be magnetized to a level that will allow the inspection
to be effective.
• The method is used to inspect a variety of product forms such
as castings, forgings, and weldments. Many different
industries use MPI for determining a component's fitness-
for-use. Some examples of industries that use magnetic
particle inspection are the structural steel, automotive,
petrochemical, power generation, and aerospace industries.
Underwater inspection is another area where magnetic particle
inspection may be used to test such things as offshore
structures and underwater pipelines.
Magnetic Particle Inspection (MPI)
https://www.youtube.com/watch?v=tlE3eK0g6vU at~1:10-2:48 MPI
https://www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/cc_mpi_index.php

11. Magnetic Particle Inspection
The part is magnetized. Finely milled iron particles coated with a
dye pigment are then applied to the specimen. These particles
are attracted to magnetic flux leakage fields and will cluster to
form an indication directly over the discontinuity. This indication
can be visually detected under proper lighting conditions.
Flux leakage
The magnetic particles form a
ridge many times wider than
the crack itself, thus making the
otherwise invisible crack visible.
Cracks just below the surface
can also be revealed.
Relative direction between the
magnetic field and the defect
line is important.
https://www.youtube.com/watch?v=qpgcD5k1494 to~3:03
https://www.youtube.com/watch?v=dQoB7jpxSe8 MPI testing procedure

12. Magnetic particles
• Pulverized iron oxide (Fe3O4) or
carbonyl iron powder can be used
• Colored or even fluorescent
magnetic powder can be used to
increase visibility
• Powder can either be used dry or
suspended in liquid

13. Examples of visible dry magnetic particle indications
Indication of a crack in a saw blade Indication of cracks in a weldment
Before and after inspection pictures of
cracks emanating from a hole
Indication of cracks running between
attachment holes in a hinge

14. Examples of Fluorescent Wet Magnetic
Particle Indications
Magnetic particle wet fluorescent
indication of a cracks in a drive shaft
Magnetic
particle wet
fluorescent
indication of
a crack in a
bearing
Magnetic particle wet fluorescent
indication of a cracks at a
fastener hole

15.  One of the most dependable and sensitive
methods for surface defects
 fast, simple and inexpensive
 direct, visible indication on surface
 unaffected by possible deposits, e.g. oil,
grease or other metals chips, in the cracks
 can be used on painted objects
 results readily documented with photo or tape
impression
Advantages of MPI

16. Limitations of MPI
 Only good for ferromagnetic materials
 sub-surface defects will not always be
indicated
 relative direction between the magnetic field
and the defect line is important
 objects must be demagnetized before and
after the examination
 the current magnetization may cause burn
scars on the item examined

17. The most commonly used
ultrasonic testing technique is
pulse echo, whereby sound is
introduced into a test object
and reflections (echoes) from
internal imperfections or the
part's geometrical surfaces are
returned to a receiver. The
time interval between the
transmission and reception of
pulses give clues to the
internal structure of the
material.
Ultrasonic Inspection
(Pulse-Echo)
In ultrasonic testing, high-frequency
sound waves are transmitted into a
material to detect imperfections or to
locate changes in material properties.
https://www.youtube.com/watch?v=tlE3eK0g6vU at~6:45-8:00 or to 11:35
https://www.youtube.com/watch?v=gqJN8tyosDw to~0:42

18. 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
Oscilloscope, or flaw detector screen
Ultrasonic Inspection (Pulse-Echo)
https://www.youtube.com/watch?v=UM6XKvXWVFA at~1:18-3:08
http://www.doitpoms.ac.uk/tlplib/piezoelectrics/applications.php
Principle of ultrasonic testing
LEFT: A probe sends a sound wave
into a test material. There are two
indications, one from the initial
pulse of the probe, and the second
due to the back wall echo.
RIGHT: A defect creates a third
indication and simultaneously
reduces the amplitude of the back
wall indication. The depth of the
defect is determined by the
ratio D/Ep
Ultrasonic Probe
Ultrasonic probe is made of piezoelectric
transducers.

19. How It Works?
At a construction site, a technician
tests a pipeline weld for defects
using an ultrasonic instrument.
The scanner, which consists of a
frame with magnetic wheels,
holds the probe in contact with
the pipe by a spring. The wet area
is the ultrasonic couplant
(medium, such as water and oil)
that allows the sound to pass into
the pipe wall.
Non-destructive testing of a swing
shaft showing spline cracking.
Spline cracking
Backwall
Spline – any of a series of projections on a
shaft that fit into slots on a corresponding
shaft, enabling both to rotate together.
Lower end Upper end
https://www.youtube.com/watch?v=UM6XKvXWVFA
at~3:08-4:10

20. Gray scale image produced using
the sound reflected from the front
surface of the coin
Gray scale image produced using the
sound reflected from the back surface
of the coin (inspected from “heads” side)
High resolution scan can produce very detailed images. Both images
were produced using a pulse-echo techniques with the transducer
scanned over the head side in an immersion scanning system.
Images obtained by C-Scan

21. Applications of Ultrasonic Inspection
Ultrasonic inspection 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.
Limitations of Ultrasonic Inspection
1. Manual operation requires careful attention by experienced
technicians.
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.
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.
6. Inspected items must be water resistant, when using water based
couplants that do not contain rust inhibitors.

22. • Eddy current testing can be used on all electrically
conducting materials with a reasonably smooth surface.
• The test equipment consists of a generator (AC power
supply), a test coil and recording equipment, e.g. a
galvanometer or an oscilloscope
• Used for crack detection, material thickness measurement
(corrosion detection), sorting materials, coating thickness
measurement, metal detection, etc.
Eddy Current Testing (ECT)
Electrical currents are generated in a conductive material by an
induced alternating magnetic field. The electrical currents are
called eddy currents because they flow in circles at and just
below the surface of the material. Interruptions in the flow of
eddy currents, caused by imperfections, dimensional changes, or
changes in the material's conductive and permeability properties,
can be detected with the proper equipment.
https://www.youtube.com/watch?v=tlE3eK0g6vU at~11:36-12:38

23. Conductive
material
Coil
Coil's
magnetic field
Eddy
currents
Eddy current's
magnetic field
Eddy Current Instruments
Voltmeter
https://www.youtube.com/watch?v=zJ23gmS3KHY to~1:24 what is Eddy current

24. •Crack Detection
•Material Thickness
Measurements
•Coating Thickness
Measurements
•Conductivity Measurements for
Material Identification
•Heat Damage Detection
•Case Depth Determination
•Heat Treatment Monitoring
Applications of ECT
Here a small surface probe is scanned
over the part surface in an attempt to
detect a crack.
https://www.youtube.com/watch?v=9A5fQtOwnzw

25. • Sensitive to small cracks and other defects
• Detects surface and near surface defects
• Inspection gives immediate results
• Equipment is very portable
• Method can be used for much more than flaw detection
• Minimum part preparation is required
• Test probe does not need to contact the part
• Inspects complex shapes and sizes of conductive materials
Advantages of ECT

26. • Only conductive materials can be inspected
• Surface must be accessible to the probe
• Skill and training required is more extensive than other
techniques
• Surface finish and roughness may interfere
• Reference standards needed for setup
• Depth of penetration is limited
• Flaws such as delaminations that lie parallel to the probe coil
winding and probe scan direction are undetectable
Limitations of ECT

27. Radiography
Radiography 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 and onto film or other media.
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.
High Electrical Potential
Electrons
-+
X-ray Generator or
Radioactive Source
Creates Radiation
Exposure Recording Device
Radiation
Penetrate
the Sample
https://www.youtube.com/watch?v=VscasN8jgfo Introduction to radiography

28. Film Radiography
Top view of developed film
X-ray film
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.
= more exposure
= less exposure
• The film darkness (density) will
vary with the amount of radiation
reaching the film through the
test object.
• Defects, such as voids, cracks,
inclusions, etc., can be detected.
https://www.youtube.com/watch?v=tlE3eK0g6vU at~3:35-6:45

29. Applications of Radiography
• Can be used in any situation when one wishes to view the
interior of an object
• To check for internal faults and construction defects, e.g.
faulty welding
• To ‘see’ through what is inside an object
• To perform measurements of size, e.g. thickness
measurements of pipes
Limitations of Radiography
• There is an upper limit of thickness through which the
radiation can penetrate, e.g. -ray from Co-60 can
penetrate up to 150mm of steel
• The operator must have access to both sides of an object
• Highly skilled operator is required because of the potential
health hazard of the energetic radiations
• Relative expensive equipment

30. Radiographic Images

31. Burn through (icicles) results when too much heat causes
excessive weld metal to penetrate the weld zone. Lumps of
metal sag through the weld creating a thick globular condition
on the back of the weld. On a radiograph, burn through
appears as dark spots surrounded by light globular areas.
Examples of radiograph

32. For More Information on NDT
The Collaboration for
NDT Education
www.ndt-ed.org
The American Society
for Nondestructive
Testing
www.asnt.org

33. Review Questions for NDT
• Applications of NDT
• What are six most common NDT methods?
• Can liquid penetrant inspection be used to detect
internal flaws? Why?
• Why relative direction between the magnetic field
and the defect line is important in magnetic
particle inspection?
• Why are couplants needed for ultrasonic
inspection (UI)? Limitations of UI?
• Advantages and disadvantages of eddy current
testing.
• What is rediography? Limitations of radiography.