Ndt Appreciation

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meCopyright 2004 WI Ltd

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)



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



Penetrant Testing

Not suitable for porous or very absorbentmaterials

Examples:Wood

Cloth

Unglazed ceramic /pottery



Basic Steps

Penetrant application

Removal of excess

penetrant

Pre-cleaning

Application of

Developer

Inspection

Post-cleaning



Penetrant Testing

Penetrating fluid (penetrant) applied tocomponent

Aerosol Spraying Immersion Brushing Electrostatic



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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d f


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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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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



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Ferromagnetic Material

Surface Defect Subsurface Internal

MT MTCANNOT BE

DETECTED BY

Magnetic Particle

Testing




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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



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Paramagnetic: Weakly attracted by magneticfield

Examples Aluminium, Tungsten andmost metals

PARAMAGNETIC

Unable to be Magnetically tested




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Ferromagnetic: Strongly attracted by magneticfield

Examples Iron, Cobalt, Nickelandtheir alloys

FERROMAGNETIC

Suitable to be Magnetically tested


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



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N S

No Flux Leakage because No change in

permeability

STEEL = 1000



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The change in permeability causes flux leakage

Flux LeakageN S

STEEL = 1000

AIR = 1

N S

Factors Affecting Flux Leakage


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g g

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



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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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Usage of Ultraviolet Light with

Fluorescent Ink in weld testing



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Cracks indications by Fluorescent Ink



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Usage of a.c. Electromagnetic Yoke with Black Ink



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Usage of MT Bench Unit with Fluorescent Ink



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Component under test with currentflow and fluorescent ink



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Usage of Prods with black ink on weld


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An alternating

current is passedthrough a coil


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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



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Defects will interrupt the eddy current

Interruption in the coil current is displayed on the set



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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


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

684630


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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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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



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Lower

density

Higher

density

Radiation Source

Film

Specimen



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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

i f i


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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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Ndt Appreciation

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Transcript of Ndt Appreciation