ME 367: Non-Destructive Testing (NDT)

Module 1
➢ Introduction to NDT
➢ Visual Inspection

Syam Prasad G
Assistant Professor
Department of Mechanical Engineering
Sreepathy Institute of Management
1 & Technology
Vavanoor, Palakkad
COURSE OBJECTIVES
 To introduce the basic principles, techniques, equipment,
applications and limitations of NDT methods such as
Visual, Penetrant Testing, Magnetic Particle Testing,
Ultrasonic Testing, Radiography, Eddy Current.
 To enable selection of appropriate NDT methods.
 To identify advantages and limitations of nondestructive
testing methods
 To make aware the developments and future trends in NDT.
Expected outcome
 The students will be able to differentiate various defect
types and select the appropriate NDT methods for the
specimen.

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 Course Outcomes
• After successful completion of the course, the students should
be able to:
COs Description
To impart knowledge on basic concepts of different types of Non –
CO1 Destructive Testing and different types of visual inspection tools used
for NDT.
CO2 To understand Liquid Penetration Inspection and its application

CO3 To understand Magnetic Particle Inspection and its application.

To understand the working principle of Ultrasonic Testing and analyse

CO4
components
Gain knowledge about Radiography Testing and spread the idea of
CO5
Films used in industrial radiography application.
To impart the knowledge about working of Eddy Current Testing and
CO6
to get an idea about principle of Thermography.

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 Testing of Materials
 Materials are tested for one or more of the following purposes:
1. To assess numerically the fundamental mechanical
properties like ductility, malleability, hardness, toughness
etc.
2. To determine data, i.e., force – deformation (or stress) values
upon which an engineer can base is design.
3. To determine the surface or sub – surface defects in raw
materials or processed parts.
4. To check chemical composition.
5. To determine the suitability of a material for a particular
application
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Testing of Materials -
Classification

Destructive Tests

Non – Destructive Tests

Process Inspection / Tests

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 Introduction to NDT
 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.
 NDT is a highly valuable technique that can save both money
and time in product evaluation, troubleshooting, and research.

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 Non-Destructive Testing
(NDT)
• The use of non - invasive techniques
to determine:
• The integrity of a material,
component or structure
• Quantitatively measure some
characteristics of an object.
• It is the testing of materials, for
surface or internal flaws or
metallurgical condition, without
interfering in any way with the
integrity of the material or its
suitability for service.

i.e. Inspect or measure without doing harm.

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Six Most Common NDT Methods
• Visual Inspection
• Liquid Penetrant Inspection (LPI)
• Magnetic Particle Inspection (MPI)
• Ultrasonic Testing (UT)
• Radiography Testing (RT)
• Eddy Current Testing (ECT)

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1. Visual Inspection

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2.Liquid Penetrant Inspection

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3.Magnetic Particle Inspection

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4.Ultrasonic Imaging

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 5.Eddy Current Testing
Coil's
Coil magnetic field

Eddy current's
magnetic field
Eddy
currents

Conductive
material
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6.Radiograpic Inspection (x-Ray)

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Comparison Between
Destructive and Non Destructive
Testing

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 Importance of NDT
1. NDT increases the safety and reliability of the product
during operation.
2. It decreases the cost of the product by reducing scrap and
conserving materials, labor and energy.
3. It enhances the reputation of the manufacturer as a
producer of quality goods. All of the above factors boost the
sales of the product which bring more economical benefits
for the manufacturer.
4. NDT is an important routine for periodic determination of
quality of the plants and structures during service.
5. This not only increases the safety of operation but also
eliminates any forced shut down of the plants.

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 Scope of NDT
 Non-destructive testing is a descriptive term used for the examination
of materials and components without changing or destroying their
usefulness.
 NDT or NDE can be used to find, size and locate surface and
subsurface flaws and defects.
 NDT plays a crucial role in everyday life and is necessary to assure
safety and reliability.
 Typical examples are found in aircraft, spacecraft (shuttle), motor
vehicles, pipelines, bridges, trains, power stations, refineries,
buildings and oil platforms which are all inspected using NDT.

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 Scope of NDT Cont..
 NDT is a Quality Assurance management tool which can give
impressive results when used correctly.
 It requires an understanding of the various methods available,
their capabilities and limitations, knowledge of the relevant
standards and specifications for performing the tests
NDT is used typically for the following reasons:
➢ Accident prevention and to reduce costs
➢ To improve product reliability
➢ To determine acceptance to a given requirement
➢ To give information on repair criteria.

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Difficulties in NDT
 Measurements are indirect and hence, reliability is to be verified
 Skilled labours are required to interpret the result
 Special devices and instruments are needed.
 It mainly involves qualitative measurements.
 It may sometimes be necessary to use one method of NDT to
confirm the findings of another.
 There may be interferences of background noises with the actual
signal.
 Difficulties like wrong positioning, orientation and wrong
determination of the defect type.
 Surface preparation is necessary.

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Economic Aspects of NDT
 It is highly Economical compared to other methods.
 Products can be reused.
 Rejection rate is less.

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Visual Inspection

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Visual Inspection
Most basic and common
inspection method.

Portable video inspection

unit with zoom allows
inspection of large tanks and
vessels, railroad tank cars,
sewer lines.

Robotic crawlers permit

observation in hazardous or
tight areas, such as air ducts,
reactors, pipelines.

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Visual Inspection

 Simplest, fastest and one of the most widely used

Non-Destructive Testing methods.
 It involves visual observation of the test specimen
to detect the presence of surface discontinuities.
 Used 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.

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 Visual Inspection means the inspection of equipment and structures
using a combination of human senses such as vision, hearing, touch
and smell.
 Visual Inspection is sometimes carried out in conjunction with
devices (Optical Aids) such as
 a low power magnifying glass/mirrors,
 microscopes
 borescopes
 endoscopes
 fiberscopes
 digital video borescopes
 camera systems (CCTV)
 robotic crawler systems.
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 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,
 whether all of the parts have been appropriately
incorporated into the device.
 Corrosion, misalignment of parts, physical damage and
cracks are some of the discontinuities which can be
detected by visual inspection.

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Basic Principle of Visual
Inspection
 Illumination of test specimen with light, usually
in the visible region.
 The specimen is then examined with eye or by
light sensitive devices such as photocells
 Equipment used for VI is extremely simple, but
adequate illumination is essential.
 The surface of the specimen should be
adequately cleaned before inspecting.

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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/fracture and
deformities of machine components
 It inspect the plant components for any leakage or
abnormal operation
 It is used to identify the defects in weldments such as
cracks, excess reinforcements, porosities etc.
 Minute discontinuities in pumps, compressors, turbo-
generator parts, instruments etc., with the help of optical
aids.

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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

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Vision

The eye
 Human eye is the most valuable NDT Tool
 Sensitivity of the human eye varies according to the light
source
 Human eye has an excellent visual perception
 Yellow green light of wavelength 5560Å is the most
suitable light for human eye at normal condition

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Lighting and Lighting source
 The amount of light is depend up on the type of
test.
 For an appropriate visual inspection, suitable
lighting of about 800-1000 Lux
 The major lighting sources are
 Incandescent Lamp
 Fluorescent lamp
 High intensity discharge lamp

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Material factors that affect Visual
Testing
 Surface Condition  Cleanliness
 Cleanliness  Humidity and
 Colour Temperature
 Safety
 Texture
 Physical Conditions  Physiological Factors
 Physical Comfort
 Specimen Condition
 Health , mental
 Shape and Size
attitude, fatigue and
 Temperature/Environm test item position
ental Factors
 Atmosphere
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Types of Visual Inspection

1. Unaided Visual Inspection

2.Aided Visual Inspection

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1. 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 mated parts

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2. 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

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 Visual Perception
 It is the interpretation of impressions transmitted
from retina of eye to the brain in terms of
information
 Visual perception depends on the vision acuity
 Human eye has an excellent visual perception

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Tools Used in Visual Inspection
 Mirrors
 Magnifying Glasses
 Microscopes
 Borescope
 Endoscope
 Flexible fibres
 Closed circuit Television system
 Computer enhanced systems

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

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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

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Microscope
 Microscope is used to
magnify the image of
a small object
 Uses a combination of
lenses.
 Magnification Power
= 10/F

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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
 Available range is 2.5 mm to 19 mm

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 Endoscope
 It is bit superior than borescope with high intensity light source.
 Magnification factor of 10X is obtained
 Available up to smaller dia of 1.7 mm and length up to 100-150mm
Fibroscopes
 Also called fibre optic borescope.
 Used to get clear & sharp images of parts and interior
surfaces which are not easily accessible.
 Diameter range of about 3 to 12.5mm and length varies
between 60 – 365 cm

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CCTV

➢ Camera, display monitors and recording devices

are connected together in a closed circuit.
➢ High resolution display
➢ Ability to zoom in/out to track the defects from the
features.

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 Special Lighting
Back Lighting
• The light source and image sensor are placed on opposite sides of
the component.
Front Lighting
• The light source and image sensor are on same side of the
component.
Structured Lighting
• Combination of light source and optical element to form a line of
light.
Strobe Lighting
• Used to image moving objects. A pulse of light illuminates the
object momentarily.
Ultraviolet Lighting
• It causes the fluorescent material to glow & is used in liquid
penetrant and magnetic particle testing for detecting
discontinuities
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Computer Enhanced Visual
System

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Computer Enhanced Visual
Inspection
 It makes use of a video camera for data collection and a
computer software for data analysis.
 The process control system controls the overall
inspection process.
 It provides the commands and timing signals to control
the system-wide data base.
 Image processing system gets the input image data from
the sensing system.
 Flaw analysis system examines the areas identified by
image processing system and determines the part
classification based on flaw decision rule.

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 Contd…

 Sensing system provides the illumination source for the

parts.
 Frame grabber card in the flaw analysis system
examines the image which is captured by camera in the
image processing system.
 The software in the computer then analyses the image
and makes a decision whether the object passes or fails
the inspection.
 The task of the inspector is reduced depending on the
level of automation.

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 Advantages of Computer Enhanced
Visual Inspection

It can be reprogrammed offline on another machine.

It can be used to inspect a wide range of products.

It can work throughout the at and doesn’t get tired.

Inspection can be done at a higher speed than a human

being.

Maintains consistency in inspection.

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 Disadvantages of Computer Enhanced
Visual Inspection

Software must be carefully selected and implemented.

Lighting conditions must be well designed.

It follows only the rules of the program and does not take
real time decisions.

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