Non-Destructive Testing (NDT)

Module 1

Hareesh K Nair
Assistant Professor
Department of Mechanical Engineering

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 Introduction to NDT
• Nondestructive testing or 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 nondestructive examination (NDE), nondestructive
inspection (NDI), and nondestructive evaluation (NDE) are
also commonly used to describe this technology.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

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 Non-Destructive Testing
(NDT)
Non-Destructive testing is the
use of noninvasive techniques to
determine the integrity of a
material, component or structure
or 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
• Liquid Penetrant
• Magnetic
• Ultrasonic
• Eddy Current
• X-ray

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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 also used widely for routine or 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 in such a way that allows materials to be
examined 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.

• 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

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 Scope of NDT Cont..
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
• However lack of skilled operators, an aging workforce and cost conscious
users are key challenge faced by Non Destructive testing market. Though
development in infrastructure and power generation have incrementally
increased demand for new operators but shortage of supply and shrinking
budget continues to …

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 Future Progress in NDT
3D characterisation
Ultrasound is the ideal vehicle for exploring the
local response of a composite structure to stress, and
map this across the whole 3D structure

Mechanical Modelling Using NDT Data

Recent developments in X-ray CT and ultrasonic 3D
characterisation of composites offer the potential for a greater
understanding of the effects on structural integrity of material
variations such as in-plane fibre waviness, out-of-plane ply
wrinkling, and 3D variations in fibre-volume fraction or porosity
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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
• 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.

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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 such as a low power
magnifying glass, boroscopes, fiberscopes,
digital video borescopes, camera systems and
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,
or whether all of the parts have been
appropriately incorporated into the device.

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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 5560°A is the most
suitable light for human eye at normal condition
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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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 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 weldments

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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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 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 • Environmental Factors
– Cleanliness – Atmosphere
– Cleanliness
– Colour
– Humidity and Temperature
– Texture – Safety
• Physical Conditions • Physiological Factors
– Specimen Condition – Physical Comfort
– Shape and Size – Health , mental attitude,
– Temperature fatigue and test item
position

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

Hareesh k,AP,Dept of ME,VAST

 Fibroscopes
• Also called fibre optic
borescope
• Dia range of about 3 to
12.5mm and length
varies between 60 – 365
cm

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 CCTV

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 Special Lighting
• Back Lighting
• Front Lighting
• Structured Lighting
• Strobe Lighting
• Ultraviolet Lighting

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Computer Enhanced Visual System

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