ndt appreciation
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NDT Methods
Penetrant Testing Magnetic Particle
Testing
Eddy Current Testing
Ultrasonic Testing
Radiographic Testing
Magnetic Flux Leakage
Acoustic Emission
Infrared Testing
Visual Testing Other methods
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NDT
Which method is the best ?Depends on many factors andconditions
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NON-DESTRUCTIVE TESTING
NDT
Definition:
A procedure, which covers the inspection and/or testing of any
mater ial, component or assembly by means, which do not affect
i ts ultimate serviceabil i ty.
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CERTIFICATIONS ANDQUALIFICATIONS
NDT personnels should posses high credibilityand integrity
Proper training and certification required
Training : By qualified training personnels andaccredited training centres
International Certification Schemes available:
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Penetrant Testing
Surface Testing method
For detecting surface breaking defects (opened tosurface)
Applicable to all materials -except for excessivelyporous (absorbing) materials
Also known asDye Penetrant Inspection (DPI)
Penetrant Flaw Detection (PFD)
Liquid Penetrant Inspection (LPI)
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Penetrant Testing:SurfaceTesting
OPEN TO SURFACE/
SURFACE BREAKING
SUBSURFACE
INTERNAL
Penetrant Testing can only detect surface breaking defects
Penetrant must be able to enter the defect to form indication
Cannot be detected by
Penetrant Testing
Maybe detected by Penetrant Testing
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Penetrant Testing
Not suitable for porous or very absorbentmaterials
Examples:Wood
Cloth
Unglazed ceramic /pottery
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Basic Steps
Penetrant application
Removal of excess
penetrant
Pre-cleaning
Application of
Developer
Inspection
Post-cleaning
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Penetrant Testing
Penetrating fluid (penetrant) applied tocomponent
Aerosol Spraying Immersion Brushing Electrostatic
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Penetrant Testing
Penetrating fluid (penetrant) applied tocomponent and drawn into defect by
capillary action
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Principle : Capillary Action
Interaction of adhesive and cohesiveforces
meniscus
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Capillarity
The ability of a material to enteropening examples: tube or defects
The formula= 2S Cos
W
= Capillary pressure
S = Surface tension
= Contact angle
W = Width of opening
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Penetrant Testing
Removal of excess penetrant
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Removal of excess penetrant
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Penetrant Testing
Application of developer
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Penetrant Testing
Penetrant drawn back out of the defect by
reverse capillary action
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Penetrant Testing
Penetrant which pulled out from the defect by the
developer forms indication of the defect
Indications
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Advantages of PT
Applicable to non-ferromagnetics
Able to test large parts with a portablekit
Batch testing Applicable to small parts with complex
geometry
Simple,cheap easy to interpret Sensitivity
i d f
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Disadvantages of PT
Will only detect defects open to thesurface
Careful surface preparation required
Not applicable to porous materials Temperature dependant
Cannot retest indefinitely
Compatibility of chemicals
S l ifi i
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System classification
PENETRANT
Colour Contrast
Fluorescent
Dual sensitivity
C l C P
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Colour Contrast Penetrant
Also known as Visible Dye Penetrant
Uses white light : Daylight or artificial white light
Bright coloured dye : usually RED
Fl t C l C t t
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Fluorescent v Colour Contrast
Fluorescent moresensitive
Less operator fatiguewith fluorescent
More difficulty inmonitoringfluorescentpenetrant removal
W t W h bl P t t
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Water Washable Penetrant
Also known as SELF-EMULSIFIED PENETRANT
Pre-mixed penetrant and emulsifier
Easily washed by water rinse
Oily
Penetrant
Emulsifier
+=
Water
Washable
Penetrant
W t W h bl P t t
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Water WashablePenetrant
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PENETRANT
WATER
SPRAY
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Penetrant been washed off
Shallow wide defectsDeep or gross defects
shows
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S l t R bl
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Solvent Removable
ADVANTAGES Portability
No water supplyneeded
DISADVANTAGES Not suited to batch
testing
Requires hand wiping
so time consuming More expensive than
water washable
Potentially hazardous
chemicals
S l t R bl
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Solvent Removable
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Post Emulsifiable Penetrant
StagesImmerse component in penetrant
Immerse component in emulsifier
Emulsifier diffuses into the penetrant making
it water washable
Water wash removes excess penetrantmixed with emulsifier
Penetrant in defects left unaffected
Post emulsifiable
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Post emulsifiable
Post Emulsifiable
Penetrant
Emulsifier
Now the surfacepenetrant is
water washable
Post emulsifiable
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Post emulsifiable
Penetrant
EmulsifierPenetrant mixed with emulsifier
Water
Spray
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Penetrant in defect not mixed with emulsifier :
NOT REMOVED
Only penetrant on the surface removed
Post emulsifiable
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Post emulsifiable
ADVANTAGES
High Sensitivity
Maximumpenetrating ability
Greater control overpenetrant removal
DISADVANTAGES
Not suitable forrough surfaces
More expensive
More timeconsuming
Developer Sensitivity
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Developer Sensitivity
Dry powder 100 - 140 % Aqueous solution 110 - 150 %
Aqueous suspension 120 - 200%
Non-Aqueous 120 - 240%
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Penetrant Systems
PENETRANT
Colourcontrast
Fluorescent
Dual
REMOVAL
Solvent
Waterwashable
Postemulsifiable
DEVELOPERS
Dry powder
Aqueous
Non-Aqueous
S l ti f S t
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Selection of System
Nature of discontinuities (size and type) Geometry and intricacy
Surface condition
Component material
Size and position
Equipment and expertise available Cost
Number of components to be tested
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Selection of System
Inspection of a large number of
threaded components
Fluorescent for mass inspections
Water washable more suited than solvents tobatch inspections
Post emulsifiable difficult to remove fromthreads
What method will you select and why ?
Fluorescent water washable with drypowder developer
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Selection of System
Inspection of turbine blades for fatigue
cracks
Fluorescent more sensitive than colour contrast Post emulsifiable more sensitive than water
washable
Non-aqueous developer most sensitive
What method will you select and why ?
Fluorescent post emulsifiable with non-aqueous developer
Penetrant Testing
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Penetrant Testing
Penetrant Testing of large aircraft components
Penetrant Testing
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Penetrant Testing
Fluorescent Penetrant Testing of small components
Penetrant Testing
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Penetrant Testing
Penetrant Testing of various small components
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Magnetic Particle Testing
Part 2
NDT Training & Certification
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Magnetic Particle Testing
Magnetism
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Magnetism
The phenomenon of certain materials which attract
certain other materials e.g.. pieces of iron to themselves
NS NS
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Test method for the detection of
surface and sub-surfacedefects
in ferromagnetic materials
Magnetic Particle Testing
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Ferromagnetic Material
Surface Defect Subsurface Internal
MT MTCANNOT BE
DETECTED BY
Magnetic Particle
Testing
Magnetic Particle Testing
Magnetic Particle Testing
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Magnetic Particle Testing
Basic Steps
Magnetic field inducedin component
Defects disrupt themagnetic flux
Defects revealed byapplyingferromagneticparticles
Lines of force
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Lines of force
By convention they flow from North toSouth outside and South to North inside
Form closed loops
Never cross
Field is strongest where most numerous
Follow path of least resistance
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N S
Definitions
Magnetic field : Region in whichmagnetic forcesexist
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Flux Density : Magnetic flux perunit cross-section area
(measured in Teslas)
Definitions
High Flux Density:
More Flux per unit
area
Low Flux Density: LessFlux per unit area
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Definitions
1 cm
1 cm
1 Tesla = 10 000 gauss
How many line of force are there in an 1 cm area with a
Flux Density of 1 Tesla?
10 000 = 10 lines
BS 6072
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BS 6072
The FLUX DENSITY on the surface of thecomponent must be at lease 0.72 T
Below that the indication will be too
weak
Below 0.72 TESLA Above 0.72 TESLA
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AMMETER
000001000500
In General:
Increasing the Magnetising Force
will increase the Magnetic Field
Measured inAmpere per meter ( A/m)
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Permeability
The ease with which a material can bemagnetised
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Permeability
A B
Magnetised using 100 amps Magnetised using 100 amps
High Permeability:
Easy to be magnetised
Low Permeability:
Difficult to be magnetised
Materials Behaviours in
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Materials Behaviours inMagnetic Field
Diamagnetic: Slightly repelled by magneticfield
Examples Gold, Copper, Water andmost non-metal
DIAMAGNETIC
Unable to be Magnetically tested
Materials Behaviours in
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Paramagnetic: Weakly attracted by magneticfield
Examples Aluminium, Tungsten andmost metals
PARAMAGNETIC
Unable to be Magnetically tested
Materials Behaviours inMagnetic Field
Materials Behaviours in
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Ferromagnetic: Strongly attracted by magneticfield
Examples Iron, Cobalt, Nickelandtheir alloys
FERROMAGNETIC
Suitable to be Magnetically tested
Materials Behaviours inMagnetic Field
Permeability
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Permeability
A unit of comparison: compared tofree space
Examples:
Air 1 Iron 560 Steel 1000 Mu Metal 80 000 Paramagnetics Slightly > 1 Diamagnetics Slightly < 1 Ferromagnetics 240 +
Other Forms of Magnet
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Other Forms of Magnet
N S
HorseshoeMagnet
Ring
Magnet
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Electromagnetism
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Electromagnetism
A current flows through a conductor and
sets up a magnetic field around it
Field is at 90oto the direction of theelectrical current
Directionof current
flow
Direction of magnetic field
Coil Magnetisation
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g
Changes circular filed into longitudinal
Increases the strength of the field
Coil Magnetisation
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Co ag et sat o
Longitudinal Magnetic Field
Detect transverse defects
Principle of MT : Flux Leakage
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Principle of MT : Flux Leakage
Ring Magnet Ring Magnet
Magnetic field is Fullycontained: No Poles
Flux Leakage occurs:Poles created
Flux
LeakageN
S
Ferromagnetic
Particles
Attractedat poles
Principle of MPI : Flux
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Principle of MPI : FluxLeakage
N S
No Defect Defect
The change in permeability causes flux leakage
N SFlux Leakage
Principle of MPI : Flux
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Principle of MPI : FluxLeakage
N S
No Flux Leakage because No change in
permeability
STEEL = 1000
Principle of MPI : Flux
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Principle of MPI : FluxLeakage
The change in permeability causes flux leakage
Flux LeakageN S
STEEL = 1000
AIR = 1
N S
Factors Affecting Flux Leakage
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Depth of defect
Orientation of defect shape of defect
Size of defect
Permeability of material Amount of flux available
Depth below surface
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Depth below surface
SN SN
Defect Orientation
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Defect Orientation
Defect at 90 degrees to flux : maximum
indication
Defect Orientation
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Defect Orientation
>45 Degrees to Flux: Acceptable
indication
Defect Orientation
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Defect Orientation
How to detect the ones missed?
All surface defects form indications
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But not all indications are
caused by defects
Non-relevantindications
Due to flux leakage but
arising from design features orgeometry
Changes in section
Changes inpermeability
Furring
Splines
Keyway
Rivet
Toe of welds
Rough
Surface
Chisel
Furring
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Furring
Caused by:
Sharp change of contour
FurringFurring
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Furring
Caused by:
Excessive flux on the surface or ends of
component
Furring
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Magnetic Writing
Caused by:
Localised polarization when magnetised object
induced the magnetic field into another object
Sp ri / F l Indi ti n
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Spurious / False Indications
Indications caused by operator errorsNot due to flux leakage
Lint
Dirt Hairs
Rele ant/ Tr e Indications
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Relevant/ True Indications
Indications caused by defects
Magnetic Particle Testing
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Cracks indications by Fluorescent Ink
Inks and Powders
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MT Inks
Black and
Fluorescent
MT Powders
Colour
contrast and
Fluorescent
Particles in Inks or Powders
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Magnetic Particle Testing
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Usage of Ultraviolet Light with
Fluorescent Ink in weld testing
Magnetic Particle Testing
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Cracks indications by Fluorescent Ink
Magnetic Particle Testing
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Usage of a.c. Electromagnetic Yoke with Black Ink
Magnetic Particle Testing
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Usage of MT Bench Unit with Fluorescent Ink
Magnetic Particle Testing
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Component under test with currentflow and fluorescent ink
Magnetic Particle Testing
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Usage of Prods with black ink on weld
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Eddy Current Testing
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An alternating
current is passedthrough a coil
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Eddy Current Testing
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y g
An alternating current is
passed through a coil A.C. generates an
alternating field
Alternating fieldgenerates eddycurrents in conductors
Eddy currents generateopposing field whichmodifies current in coil
Eddy Current Testing
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Defects will interrupt the eddy current
Interruption in the coil current is displayed on the set
Eddy Current Testing
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Equipment
Eddy Current
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y
Electrical currents induced in metals byalternating magnetic fields
The size of the current is affected by
Electrical conductivity
Stand off distance
Flaws
Permeability
Specimen dimensions
Advantages of ET
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Sensitive to surface defects Can detect through several layers
Can detect through surface coatings
Accurate conductivity measurements Can be automated
Little pre-cleaning required
Portability
Disadvantages of ET
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Very susceptible to permeability changes
Only on conductive materials
Will not detect defects parallel to surface
Not suitable for large areas and/orcomplex geometry's
Signal interpretation required
No permanent record (unless automated)
Expensive equipment
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Ultrasonic Testing
NDT Training & Certification
Ultrasonic Testing
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High frequencysound sound wavesare introduced into amaterial
Reflected soundgives information onthe material undertest and signalsdisplayed on a CRT
Principle
Basic Principles of Ultrasonic Testing
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Sound is transmitted in the material to be testedThe sound reflected back to the
probe is displayed on
the Flaw Detector
Basic Principles of Ultrasonic Testing
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The distance the sound traveled can be displayed on the Flaw Detector
The screen can be calibrated to give accurate readings of the distance
Bottom / Backwall
Signal from the backwall
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The depth of the defect can be read with reference
to the marker on the screen
0 10 20 30 40 50 60
60 mm
Thickness / depth measurement
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A
A
B
B
C
C
The THINNER the material
the less distance the sound
travel
The closerthe reflectorto the surface, the
signal will be more to
the leftof the screen
The thickness is read from the screen
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Ultrasonic Testing Applications
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Probes
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Probe Design
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Compression Probe
Normal probe
0
Damping
Transducer
Electricalconnectors
Housing
Probe Design
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Shear Probe
Angle probe
DampingTransducer
Perspex wedge
Backing
medium
ProbeShoe
Probe Design
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Twin Crystal
Advantages
Can be focused Measure thin plate
Near surfaceresolution
Disadvantages
Difficult to use oncurved surfaces
Sizing small defects Signal amplitude /
focal spot length
Transmitter Receiver
Focusing
lensSeparator /
Insulator
Gap Scanning
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Probe held a fixed
distance above thesurface (1 or 2mm)
Couplant is fed intothe gap
Immersion Testing
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Component is placed
in a water filled tank Item is scanned with
a probe at a fixeddistance above the
surface
Immersion Testing
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Waterpath
distance
Water path distance
Front surface Back surface
Defect
AUTOMATIC ULTRASONIC TESTING SYSTEM
C Scan Presentation
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C-Scan Presentation
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P-Scan Image Presentation
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g
T-Scan Image Presentation
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g
TOFD
Time of Flight Diffraction
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TOFD Images
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rea Monitoring
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May 1999: tmin = 29.6 mm Dec. 1999: tmin = 29.6 mm
June 2000: tmin = 29.4 mm April 2001: tmin = 29.2 mm
Methods of Setting Sensitivity
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Smallest defect at maximum test range Back wall echo
Disc equivalent
Grass levels Notches
Side Drilled Holes, DAC Curves
Scanning Procedure
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Parent Material
0 degree both sides
To maximum range for angle probes
Full skip distance for 60 or 70 probes
Scanning Procedure
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Weld RootHalf skip from both sides
For PCN exams :
70 degree probe at half skip from both sides
Scanning ProcedureWeld Fusion Faces
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Weld Fusion Faces
Half to full skip from both sides
A probe which strikes fusion faces at 90 degrees
Probe angle = 90 - (1/2 Root angle)
Scanning Procedure
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Weld Body
Half skip to full skip from both sides
Full Skip 1/2 Skip
Scanning Procedure
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Transverse
70 degree
Nozzle Welds
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Scanning procedure
Tee butt welds
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Pulse Echo Technique
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Single probe sends
and receives sound Gives an indication
of defect depth anddimensions
Not fail safe
Defect Position
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No indication from defect A (wrong orientation)
AB
B
Through Transmission Technique
T
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Transmitting and
receiving probes
on opposite sidesof the specimen
Tx Rx
Presence of defect
indicated by
reduction intransmission signal
No indication of
defect location
Fail safe method
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Through Transmission Technique
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Advantages
Less attenuation
No probe ringing
No dead zone Orientation does not
matter
Disadvantages
Defect not located
Defect cant be
identified Vertical defects dont
show
Must be automated
Need access to bothsurfaces
Transmission with Reflection
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RT
Also known as:
Tandem Techniqueor
Pitch and Catch Technique
Advantages of UT
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Sensitive to cracks at various
orientations Portability
Safety
Able to penetrate thick sections Measures depth and through wall
extent
Disadvantages
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No permanent record (unless automated)
Not easily applied to complex geometriesand rough surfaces.
Unsuited to course grained materials
Requires highly skilled and experiencedtechnicians
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Radiographic Testing
NDT Training & Certification
Radiographic Testing
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Electromagnetic radiation is imposedupon a test object
Radiation is transmitted to varyingdegrees dependant upon the density ofthe material through which it istravelling
Variations in transmission detected by
photographic film or fluorescent screens Applicable to metals,non-metals and
composites
Radiographic Testing
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Lower
density
Higher
density
Radiation Source
Film
Specimen
Radiographic Testing
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PlacingFilm to be radiographed
Radiation Sources
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Isotopes produce Gamma rays
Examples: Co60, Ir192, Yb169
X-Ray Tube
ELECTROMAGNETIC SPECTRUM
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10-10 10-8 10-6 10-4 10-2 1cm 102 104 106 108
Wavelength
Electric
Waves
TV
Microwaves
Infra redUltra
violet
Industrial
radiography
Shorter Wavelength = Increased Energy
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Shortening Wavelength
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X-RAY
PRODUCTION
X-Ray Production
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-ve +ve
X-RAYFOCUSING CUP
C
U
RR
E
N
T
TUNGSTEN
TARGET
CATHODE ANODE
X-RAY PRODUCTION
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CATHODE
. PROCESS THAT MAKE THEELECTRON BOILS OUT FROM THEHOT WIRE IS CALLED THERMIONICEMISSION
2. IT IS CONTROLLED BY THE MILIAMP
CONTROL THAT SUPPLY CURRENTTO THE CATHODE
3. INCREASED THE CURRENT, WILLINCREASED THE INTENSITY OF THEELECTRON STREAM AND HENCE THERADIATION
ANODE
1. INCLINED TUNGSTEN TARGETEMBEDDED IN A LARGE LUMP OFCOPPER
2. USED AS A TARGET FOR THEELECTRON TO HIT,AND THE
IMPACT WILL PRODUCE X-RAYSAND HEAT.
3. VOLTAGE THAT SUPPLY TO THEANODE IS CONTROLED BY THEkV CONTROL.
4. THE HIGHER THE VOLTAGEACROSS THE TUBE,THE HIGHERTHE VELOCITY OF THEELECTRONS AND THE GREATERTHE PENETRATING POWER
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RADIOACTIVEISOTOPES
Radioactive isotope
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It is small,typically 1mm x 1.5 mm
cylinders,that give off gamma rays It occurs in nature and also in artificial
isotopes
Artificial isotopesare created by
bombarding an element with an excess ofneutron in the nuclear reactor.
Example of nature isotopes are radium anduranium
Example of artificial isotopes are iridium192 and cobalt 60
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RADIOGRAPHIC FILM
IT HAS TWO TYPES
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IT HAS TWO TYPES
SLOW FILM- FINE GRAIN AND NEED MORE EXPOSURE
FAST FILM
- LARGE GRAINS AND NEED LESS EXPOSURE
KNOWLEDGE OF FILM CAN HELPS THERADIOGRAPHER TO WORK OUT EXPOSURES WHENCHANGING FILMBRANDS. E.G IN TABLE 5.3
FILM ALSO SHOULD BE STORED IN EDGES, IN COOLDRY CONDITIONS AND AWAY FROM CHEMICALS ORRADIATION
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THREE LAYERS
PROTECTIVE LAYER
LAYER OF GELATIN PROTECTS THE
EMULSION LAYER FROM
SCRACTHES
EMULSION LAYER
SUSPENDED IN IT THE SILVER
BROMIDE..
TRANSPARENT POLYSESTER
BASE OF RADIOGRAPHY
RADIOGRAPHIC FILM
EXPOSED
SILVER BROMIDE WILL
BE EXPOSED
THE IMAGE IS LATENT
AND NO VISIBLE CHANGE
IN FILM .IT WOULD BE
NOTICEABLE UNTIL
DEVELOPMENT
PROCESSING FILM
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Developer
St
op
ba
thRunning water
MANUAL SYSTERM
Radiographic Image
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TechniquesPanoramic
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Single Wall Single Image
Double Wall Double Image
Gamma Rays vs. X-Rays
S f t
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Safety
X-ray machines is normally safer: can be switched off/onGamma source: constant emission
CapabilitiesGamma source have very high penetrating power
X-ray: intensity and wavelength can be adjusted
Quality of imagesIn general: x-ray produces better quality
HandlingGamma sources are easier to handle
X-ray machine are bulky, fragile and requires electricity
CostGamma source are cheaper
Radiographic Variables
D it
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Density
The degree of film darkness Contrast
The differences in density between theregions of the film
Advantages of Radiography
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Permanent record Detection of Internal flaws
Can be used on most materials
Direct image of flaws
Real - time imaging
Disadvantages of Radiography Health hazard
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Sensitive to defect
orientation Limited ability to detect fine
cracks
Access to both sides
required Limited by material
thickness
Skilled interpretation
required Relatively slow
High capital outlay andrunning costs
Acoustic Emission
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Transient stress waves from micro
structural changes detected by sensors
Stress waves
Stress
V d i hi b
Vacuum Box Testing
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Vacuum created within a perspex box
Soapy liquid applied to surface
Vacuum Box Testing
V t d ithi b
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Bubbles indicate through thicknessdefect
Vacuum created within a perspex box
Soapy liquid applied to surface
Training & Certification
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Any Questions Please ?
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