19. Non Destructive Testing

7/29/2019 19. Non Destructive Testing

1/91

Copyright 2004, TWI Ltd World Centre for Materials Joining Technology

TWICSWIP 3.1

WIS 5WELDING INSPECTION

NDT.


2/91


Surface Testing

Dye Penetrant Inspection

Magnetic Particle InspectionEddy Current Inspection

.


3/91


Volumetric Inspection

Ultrasonic Inspection

Radiographic Inspection.


4/91


Dye Penetrant Inspection


5/91


Liquid Penetrant Inspection

Surface inspection method

Applicable to all non-porous,non-absorbing materials

A.K.A. Dye Penetrant Inspection (DPI)

Penetrant Flaw Detection (PFD)

Penetrant Testing (PT)


6/91


Penetrant Inspection

Penetrating fluid appliedto surface of component


7/91Copyright 2004, TWI Ltd World Centre for Materials Joining Technology


Penetrating fluid enters defectby means of capillary action



Excess penetrantremoved from surface




Developer applied tosurface




Development time forindications to appear onsurface




System classification

Type of penetrantMethod of penetrant removalType of developer




Advantages of Penetrant Inspection

Applicable to non-ferromagnetic materials

Able to test large parts with portable kit

Suitable for batch testing

May not require electricity or water

Applicable to small parts with complexgeometry

Simple, cheap and easy to interpret

Sensitivity



Disadvantages of Penetrant Inspection

Will only detect defects open to thesurface

Requires careful surface preparation

Not applicable to porous surfaces

Temperature dependant

Cannot retest indefinitely

Compatibility of chemicals



System Classification - Penetrant

Colour contrast

Fluorescent

Dual




System Classification - Removal

Solvent

Water washable

Post emulsifiable




System Classification - Development

Dry powder

Aqueous

Non aqueous (solvent based)



Fluorescent v Colour Contrast

Fluorescent more sensitive

Less operator fatigue with fluorescent

More difficulty in monitoring excesspenetrant removal

Requires UV-A lamps, with subduedbackground lighting for fluorescent



Magnetic Particle Inspection



Magnetism Materials will strongly attract pieces

of iron to themselves

Phenomenon discovered in theancient Greek city of Magnesia

Magnets utilised in navigation

Oersted discovered the link betweenelectricity and magnetism

Faraday revealed that electrical andmagnetic energy could beinterchanged


20/91


Magnetic Particle Inspection

Test method for the detection of surfaceand sub-surface indications in

ferromagnetic materials Magnetic field induced in component

Defects disrupt the magnetic flux

Defects revealed by applyingferromagnetic particles


21/91


Principle of MPI : Flux Leakage

N S SN

No Defect Defect


22/91


Permeability of Material

Paramagnetic:Weakly attracted by magnets

Examples: Aluminium,Tungsten

Diamagnetic:Slightly repelled by magnetsExamples Gold,Copper and Water

Ferromagnetic:Strongly attractedExamples Iron,Cobalt and Nickel


23/91


Magnets

N

Lines of force / Lines of flux

S


24/91


Electromagnetism

A current flows through a conductorand sets up a magnetic field around it

Field is at 90o to the direction of theelectrical current

Directionof currentflow

Direction of magnetic field


25/91


Depth below surface

SN SN


26/91


Defect Orientation

Defect at 90 degrees to flux : maximum

indication


27/91


Defect Orientation

>45 Degrees to Flux: Acceptableindication


28/91


Defect Orientation


29/91


30/91


Equipment

Permanent Magnet

Electromagnets


31/91


Longitudinal field between poles

Defects detected at 90 degrees to poles

Permanent Magnet


32/91


Advantages No power supply

No electrical contactproblems

Inexpensive

No damage to testpiece

Lightweight

Disadvantages Direct field only

Deteriorate over time

No control over fieldstrength

Poles attract detectingmedia

Tiring to use

Permanent Magnet


33/91


Electromagnetism

A current flows through a conductorand sets up a magnetic field around it

Field is at 90o to the direction of theelectrical current

Directionof currentflow

Direction of magnetic field


34/91


Coil Magnetisation

Changes circular field into longitudinal

Increases the strength of the field


35/91


Electromagnets

Soft iron laminates within a coil.

Defects detected at 90 degrees to poles


36/91


Electromagnets

Advantages AC,DC or rectified

Controllable field

strength No harm to test piece

Can be used todemagnetise

Easily removed

Disadvantages Power supply required

Longitudinal field only

Carry mains supply Poles attract particles

Legs must have areacontact


37/91


Demagnetisation

Required if

Rotating parts

Components to be welded,machined orelectroplated

Aircraft parts

Removal of residual magnetisation

Check for removal with Field strengthmeter (magnetometer)


38/91


39/91


Eddy Current Inspection

Coil Coilsmagnetic

fieldEddy

currents

Eddy

currentsmagnetic

fieldsConductive

material


40/91



An alternating current

is passed through a coil

A.C. generates analternating field

Alternating fieldgenerates eddy currentsin conductors

Eddy currents generateopposing field whichmodifies current in coil


41/91



Electrical currents induced in metalsby alternating magnetic fields

The size of the current is affected by:-

Electrical conductivity

Stand off distance

Flaws

Permeability

Specimen dimensions


42/91


Advantages

Sensitive to surface defects

Can detect through several layersCan detect through surface coatings

Accurate conductivity measurements

Can be automatedLittle pre-cleaning required

Portability



43/91


DisadvantagesVery susceptible to permeability changes

Only works on conductive materials

Will not detect defects parallel to the surface

Not suitable for large areas and /or complex geometry

Signal interpretation required

No permanent record (unless automated)



44/91


Ultrasonic Inspection


45/91


46/91


Acoustic Spectrum

Human

16Hz - 20kHz

Ultrasonic Range

+ 20kHz

Testing

0.5MHz - 50MHz


47/91


There are three Principlewaveforms used in ultrasonicinspections

Compression

Shear

Surface

Principle waveforms in ultrasonic


48/91


Compression waves

Vibration and propagation in the samedirection

Travel in solids, liquids and gases

Propagation

Particle vibration


49/91


50/91


Surface Waves

Elliptical vibration

Velocity 8% less than shear

Penetrate one wavelength deep


51/91


Sound travelling through a material

Velocity varies according to the material

Compression waves

Steel 5960m/sec

Water 1490m/sec

Air 344m/sec

Copper 4700m/sec

Shear waves

Steel 3245m/sec

Water NA

Air NA

Copper 2330m/sec


52/91


Probe Design

Probe housing

Transducer

Electrical connections

Damping

Wear shoe


53/91


Probe Design

Shear Wave

DampingTransducer

Perspex wedgeShear wave


54/91


55/91


Pulse Echo Testing

Single probe sends and receives sound

Gives an indication of defect depth anddimensions

Not fail safe


56/91


Sound travels throughthe steel block at5.9Km/sec.

The returning sound

vibrates the crystal,which produces anelectrical pulse which isamplified and is shownon the cathode ray

tube.

Pulse Echo Testing


57/91


If a large defect ispresent all thesound will be

returned to theprobe.

The signal on theCRT can show the

depth of thedefect.

Pulse Echo Testing


58/91


If a smaller defectis present some ofthe sound will be

returned to theprobe, some willcontinue to theback wall.

Note the reductionin size of the defectsignal

Pulse Echo Testing


59/91


Defects parallel to the surface will reflect sound back to

the probeDefects at an angle to the surface will reflect thesound at an angle

The signal will not appear on the CRT

Pulse Echo Testing


60/91


Angle probes used to reflect soundoff inclined defects

Pulse Echo Testing

l h i


61/91


Angle probes used to testwelds

Pulse Echo Testing


62/91



63/91


Through Transmission Testing


64/91


Through Transmission Testing

Immersion Testing


65/91


Immersion Testing

Waterpathdistance

Water path distance

Front surface Back surface

T i i ith R fl ti


66/91


Transmission with Reflection

T R

i i i h fl i


67/91


Transmission with Reflection

T R

Ti f Fli ht Diff ti


68/91


Time of Flight Diffraction

Ti f Fli ht Diff ti


69/91


Time of Flight Diffraction

Ti f Fli ht Diff ti (TOFD)


70/91


Time of Flight Diffraction (TOFD)



71/91


The echo amplitude is displayed as grey for zero, black formaximum negative and white for maximum positivesignals

D-scan is made up of dozens of

A-scans set side by sideTop of defect




72/91


AdvantagesDoes not depend on defect orientation

Defect height can be exactly determined

Inspection results are immediately available

Permanent print is available

Higher test speed means costs are less




73/91


Disadvantages

The weld must be reasonably accessiblefrom both sides

There is a dead zone for defect detectionclose to the surfaces

Is more a sizing tool than a detecting tool


Radiographic Inspection


74/91





75/91



X or Gamma radiation is imposed upona 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 andcomposites



76/91



Lowerdensity

Higherdensity



77/91


Radiograph of weld showing:-

Crack

Slag

Lack of fusion

Porosity

Undercut




78/91


Advantages Permanent record

Internal flaws

Can be used on most materials

Direct image of flaws

Real - time imaging




79/91


Disadvantages

Health hazard

Sensitive to defect orientation

Limited ability to detect fine cracksAccess to both sides required

Limited by material thickness

Skilled interpretation required Relatively slow

High capital outlay and running costs



80/91

Electromagnetic Spectrum


81/91


Electromagnetic Spectrum

TV

Microwaves

Infra

red

Ultra

violet

Industrialradiography ElectricWaves

X-Ray Production


82/91


X-Ray Production

+ve-ve

X-ray tube isevacuated to create avacuum

Disadvantages of Gamma over X rays


83/91


Disadvantages of Gamma over X rays

Poorer quality radiographs

Exposure times can be longer

Sources need replacing

Radiation cannot be switched off

Poorer geometric unsharpness

Remote handling necessary

Radiographic Techniques


84/91


Radiographic Techniques

Single Wall Single Image(SWSI)

Double Wall Single Image(DWSI)

Double Wall Double Image(DWDI)

Advantages of Gamma over X rays


85/91


Advantages of Gamma over X rays

No electrical or water supplies neededEquipment smaller and lighter-More portable

Equipment simpler and more robust

More easily accessed

Less scatter

Equipment initially less costly

Greater penetrating power

Radiographic Technique


86/91



Single wall, single image (SWSI)

Panoramic



87/91


Double wall, single image (DWSI)

Double wall, double image (DWDI)




88/91


DWSI DWDI



89/91


90/91


91/91

19. Non Destructive Testing

Documents

Transcript of 19. Non Destructive Testing