Non Destructive Testing

Non Destructive
Testing
Devang Gandhi
Roll No : 001211301015
B. Met. Engg. 4th
Year
Jadavpur University

OUTLINE
 Introduction
 Advantages
 Industrial Use
 Types
 Applications
 Reliability
 Performance
 Market
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Introduction
 Non Destructive Testing involves techniques based on application of
physical principles employed for purpose of determining characteristics
of materials or components and for detecting and assessing
inhomogeneity and harmful defects without changing the usefulness of
materials or components.
 The methods used may be simple or intricate.
 It plays a vast role in quality control of finished product.
 Skilled judgments and experience is required while performing NDT.
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Industrial Use
 Inspection of Raw Products – Forgings, Castings, Extrusions.
 Inspection following Secondary Processing – Machining, Welding, Grinding,
Heat Treatment, Plating.
 Inspection for In-Service Damage – Cracking, Corrosion, Erosion/Wear, Heat
Damage.
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Visual Examination
 Primary method of NDT
 A simple visual test reveals gross surface defects.
 Physical Principle : Illumination of the test specimen with light.
 Equipments used are very simple and portable.
 Most Valuable NDT Tool – Human Eye.
 Mainly performed to obtain the general condition of components.
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Methodology
Instruments for Visual Examination
Use of Optical Instuments : Magnify defects, permit visual checks of unaccessible
areas, presence of foreign objects, formation of corrosive layer or even damage.
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Applications
 Inspection of plant components for leakage.
 Misalignment in equipment parts.
 Corrosion, erosion, cracks, fracture.
 Minute discontinuities on parts like pumps, compressors.
Limitations
 Detects only surface defects.
 Cannot be used at places with bright exposure or no light.
 Equipments cannot be exposed to hazardous places.
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Liquid Penetrant Testing
 Any material with relatively smooth, non porous surface on which discontinuities
or defects are present.
 Physical Principle : Capillary Action of Liquid.
 Use of Penetrant, Developer and Cleaner on test specimen.
 Defects open to surface like cracks after rolling, casting, weld cracks, hot tears,
cold shuts, shrinkages can be detected.
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Methodology
Use of Penetrant and Developer : Penetrant enters discontinuities and cracks by
capillary action mechanism and a developer is used to pull penetrant to surface.
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Applications
Limitations
 Detects only surface defects. Requires smooth, non porous material.
 Penetrant used should neither be highly viscous nor less viscous.
 Pre-cleaning is critical. Contaminants can mask defects.
 Post-cleaning is essential to remove the chemicals.
 For surface defects and flaw detection.
 Applied on materials during in-service testing.
 Large surfaces can be detected easily with low cost and short time.
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Magnetic Particle Testing
 Testing performed on Ferromagnetic materials with a smooth surface.
 Fast approach, relatively easy to apply and surface preparation is not critical.
 Physical Principle : Magnetization (Faradays Law of Magnetic Induction)
 Applicable for surface, sub-surface defects and all other defects (excluding
transverse direction)
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Applications
 Non Magnetic subsatnces cannot be evaluated.
 Avoid local heating and burning of substances.
 Demagnetization is important after performing the test.
Limitations
 Detection on Ferromagnetic materials only.
 Cracks oriented perpendicular to the current direction best observed.
 Sensitivity also depends on the type of current used.
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Eddy Current Testing
 Applied to electrically conducting materials for defect detection.
 Sensitive to small cracks and near surface cracks.
 Physical Principal : Electromagnetism.
 Used for sorting materials, control of dimensions, measuring coating thickness.
Eddy Currents
Magnetic Field
From Probe
Test
Material
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Methodology
Magnetic Field
From Test Coil
Magnetic Field
From
Eddy Currents
Eddy Currents
Crack
Conductive
Base Metal
Nonconductive
Coating
Eddy Currents
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Applications
 In-service examination of Heat Exchanger tubes.
 Material sorting and Coating thickness.
 Estimating the distribution of hardness and strength.
Limitations
 Only for electrically conducting material.
 Too many parameters affect the eddy probe impedance.
 For critical applications, results need to be verified by another NDT method.
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Radiography
 Involves use of penetrating X- Ray or Gamma Rays to examine volumetric defects.
 Source of Radiation – X-ray machine or Radioactive isotopes.
 Physical Principle : Penetrating power of High Frequency Wave.
 Resulting shadowgraph is in the visible region zone.
 Material thickness and density change are indicated on the film.
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Methodology
High Electrical Potential
Electrons
-+
X-ray Generator
or Radioactive
Source Creates
Radiation
Exposure Recording Device
Radiation
Penetrate
the Sample
= more exposure
= less exposure
Top view of developed film
X-ray film
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Applications
 Whenever interior of an object needs to be checked.
 To check internal faults and construction defects.
 To perform measurements of size, i.e. thickness.
Limitations
 Upper Limit of Thickness through which radiation can penetrate.
 Access to both sides of the object must be available.
 Relatively expensive equipment and needs skilled operator.
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Ultrasonic Testing
 Use of High Frequency Sound Waves to detect imperfections or to locate changes
in material properties.
 Time travel between transmission and reception of pulses gives clues regarding
internal structure of the material.
 The probe used is of split type, having transmitter on one end and receiver on the
other end.
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Methodology
 The reflected sound energy versus time plot is shown on the oscilloscope screen.
 The high trace indicate full thickness of the test-piece whereas the short trace
indicates the crack.
plate
crack
0 2 4 6 8 10
initial
pulse
crack
echo
back surface
echo
Oscilloscope, or flaw
detector screen
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Applications
 Applicable to almost all materials.
 Testing can be carried out from one accessible surface only.
 At a time, very large section thickness can be evaluated.
Limitations
 Test method is operator dependent. Needs highly skilled operator.
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Applications
NDT Method Used : Eddy Current
Heat Exchanger Tubes
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Applications
NDT Method Used : Magnetic Particle
Cable Wires
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Applications
NDT Method Used : Ultrasound
Storage Tank Body
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Applications
NDT Method Used : Eddy Current
Thin Outer Body of Aircraft
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Applications
NDT Method Used : Fluorescent Penetrant
Innumerous Engine Parts
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Applications
NDT Method Used : Magnetic Particle
Railway Tracks
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Applications
NDT Method Used : Acoustic Emission
Bridge Cables
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Applications
NDT Method Used : Radiography
Inner Surface of Pipes
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Applications
NDT Method Used : Radiography
Pressure Vessels
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Reliability
Major Factors affecting Reliability :
Size of Defect
type of NDT used
Inspection Environment
Quality of Equipment
Capability of Operator.
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Performance
Legend : Good – Recommended NDT Method
Moderate – NDT Method Can Be Applied
Bad – NDT Method Not Used Normally
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Market of NDT
 Non Destructive Testing Market is estimated to grow at a CAGR of 3.5% to reach
the worth $1720.96 Million by 2020.
 Major Revenue Generating Regions – U. S. and Europe.
 Latin America and Asia-Pacific are emerging markets.
 Brazil, India and China have immense growth potential for NDT.
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THANK YOUTHANK YOU
DevangGandhi

Non Destructive Testing

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Non Destructive Testing