NDT_2 [Compatibility Mode].pdf

NONNON--DESTRUCTIVE TESTINGDESTRUCTIVE TESTING

Ali Ourdjini, UTM - 2006Faculty of Mechanical Engineering

ULTRASONIC INSPECTIONULTRASONIC INSPECTION


UltrasonicUltrasonic inspectioninspection usesuses soundsound waveswaves ofof shortshort wavelengthwavelength andand highhighfrequencyfrequency toto detectdetect surfacesurface andand subsurfacesubsurface defectsdefects

ItIt isis alsoalso usedused toto measuremeasure materialmaterial thicknessthickness..

ItIt isis usedused onon aircraft,aircraft, powerpower stationsstations generatinggenerating plants,plants, oror weldswelds ininpressurepressure vesselsvessels atat anan oiloil refineryrefinery oror paperpaper millmill


UTUT involvesinvolves thethe generationgeneration ofof ultrasonicultrasonic waveswaves..

HowHow areare ultrasonicultrasonic waveswaves areare generated?generated?

GenerationGeneration ofof ultrasonicultrasonic waveswaves involvesinvolves thethe useuse ofof transducerstransducers..

AA transducertransducer isis aa devicedevice whichwhich convertsconverts energyenergy fromfrom oneone formform totoanotheranother


InIn generatinggenerating ultrasonicultrasonic waves,waves, ultrasonicultrasonic transducerstransducers convertconvertelectricalelectrical energyenergy toto mechanicalmechanical energy,energy, whichwhich inin thisthis casecase isis acousticalacoustical(vibrational)(vibrational) energyenergy..

TheThe mostmost commonlycommonly usedused transducerstransducers areare thethe piezopiezo--electricelectric..


MostMost piezopiezo--electricelectric materialsmaterials areare basedbased onon ceramicsceramics::

BariumBarium TitanateTitanate (BaTi)(BaTi)

LeadLead ZirconateZirconate TitanateTitanate (PZT)(PZT)

LeadLead MetaniobateMetaniobate (PMN)(PMN)


AA thinthin diskdisk isis thethe mostmost commoncommon shapeshape ofof piezopiezo--electricelectric ceramicceramic thatthat isis usedused forforNDTNDT applicationsapplications..

ItIt worksworks likelike thisthis:: AnAn electricelectric fieldfield appliedapplied toto thethe diskdisk throughthrough leadlead solderedsoldered totoitsits facesfaces (Figure(Figure below)below) willwill causecause aa changechange inin thethe thicknessthickness ofof thethe diskdisk..

TheThe diskdisk willwill eithereither contractcontract oror expandexpand.. ThisThis willwill generategenerate aa longitudinallongitudinal wavewavenormalnormal toto thethe diskdisk..


InIn UTUT twotwo transducerstransducers areare usedused:: TransmitterTransmitter && ReceiverReceiver

Electrical current ONElectrical current ONElectrical current OFFElectrical current OFF


Ultrasonic wave generationUltrasonic wave generation



However,However, inin mostmost casescases onlyonly oneone transducertransducer isis necessarynecessary andand actsacts asasbothboth transmittertransmitter andand receiverreceiver..

UltrasonicUltrasonic waveswaves areare transmittedtransmitted asas aa seriesseries ofof pulsespulses ofof shortshortdurationduration andand duringduring thethe timetime intervalinterval betweenbetween transmissions,transmissions, thethecrystalcrystal (transducer)(transducer) cancan detectdetect reflectedreflected signalssignals..


crystalcrystal (transducer)(transducer) cancan detectdetect reflectedreflected signalssignals..

WavesWaves typestypes andand ModesModes ofof PropagationPropagation

UltrasonicUltrasonic waveswaves areare classifiedclassified intointo fourfour typestypes (based(based onon thethe modemode ofofvibrationvibration ofof thethe particlesparticles ofof thethe mediummedium withwith respectrespect toto thethe directiondirection ofofthethe waves)waves)


Longitudinal (compression) (most widely used)

Particles displacement is in the direction of wave propagation

Easier to generate

Transverse (Shear)

Particles displacement is normal to the direction of wave propagation

Velocity is only ~ 50% of longitudinal waves

Surface (Rayleigh)


Surface (Rayleigh)

Generated near the surfaceGenerated near the surface

Follow complex curvatures (where defects can be difficult to be accessible by Follow complex curvatures (where defects can be difficult to be accessible by longitudinal or transverse waves) longitudinal or transverse waves)

Lamb (Plate)

Generated in thin plates. Generated in thin plates.

Generated when a surface wave is introduced into a material that has a thickness Generated when a surface wave is introduced into a material that has a thickness 3 3 wavelengths of the wavewavelengths of the wave


SoundSound waveswaves atat InterfacesInterfaces

1. Reflection and Transmission

There are limits for sound propagation at an interface between two


There are limits for sound propagation at an interface between twomedia having different elastic properties.

When an incident wave reaches the interface between two materials,part of the incident wave will be reflected back and a part will betransmitted across the interface.


TheThe portionportion ofof soundsound waveswaves transmittedtransmitted andand reflectedreflected isis aa functionfunction ofofthethe acousticacoustic propertiesproperties ofof thethe materialsmaterials..

ImpedanceImpedance isis frequentlyfrequently usedused toto describedescribe thethe waveswaves transfertransfer atatinterfacesinterfaces..


AcousticAcoustic impedanceimpedance (Z)(Z) isis thethe resistanceresistance toto thethe propagationpropagation ofof ananultrasonicultrasonic wavewave byby aa materialmaterial..

Z = Z = CC

CC isis thethe wavewave speed,speed, isis thethe densitydensity ofof materialmaterial


ReflectionReflection ofof soundsound atat anan airair // metalmetal interfaceinterface isis 100100%% atat thethefrequencyfrequency normallynormally usedused inin UTUT.. Thus,Thus, soundsound cannotcannot bebe transmittedtransmittedeasilyeasily intointo aa metalmetal acrossacross anan airair gapgap..

ToTo overcomeovercome this,this, aa fluidfluid suchsuch asas oiloil oror waterwater isis usedused asas aa couplingcouplingagentagent betweenbetween thethe transducertransducer andand thethe metalmetal toto bebe testedtested..


Use of couplingUse of coupling


i i

Interface

Medium 1

Reflected

compression

wave

Incident

compression

wave2.2. Reflection and RefractionReflection and Refraction

Wave transmission at some Wave transmission at some angle to the interface is of angle to the interface is of considerable importance in considerable importance in


rs

rc

Interface

Medium 2

Refracted

shear wave

Refracted

compression

wave

Reflection and refraction at an interface Reflection and refraction at an interface between two mediumsbetween two mediums

considerable importance in considerable importance in UT.UT.

The portion of the wave The portion of the wave which is transmitted across which is transmitted across the interface will be refractedthe interface will be refracted


There may be two refracted waves: There may be two refracted waves: compression compression and and shear shear

In UT the presence of two types of waves with different speeds will In UT the presence of two types of waves with different speeds will give confusing resultsgive confusing results

Therefore, the angle of incidence, i, is adjusted to be greater than the Therefore, the angle of incidence, i, is adjusted to be greater than the


Therefore, the angle of incidence, i, is adjusted to be greater than the Therefore, the angle of incidence, i, is adjusted to be greater than the critical angle, i, critical angle, i,

Probe ConstructionProbe Construction

Several types of probes are used in UT.Several types of probes are used in UT. Normal ProbesNormal Probes Angle probesAngle probes


EachEach probeprobe consistsconsists ofof aacrystalcrystal placedplaced inin contactcontact withwiththethe materialmaterial underunder testtest..

11.. NormalNormal probesprobes::

ThisThis typetype ofof probeprobe


ThisThis typetype ofof probeprobetransmittransmit longitudinallongitudinalwaveswaves..

22.. AngleAngle probesprobes

DesignedDesigned toto transmittransmitshearshear andand surfacesurfacewaveswaves..


Types of Display Types of Display

The information obtained during an The information obtained during an ultrasonic test ultrasonic test can be displayed in can be displayed in three different presentation styles:three different presentation styles:

A scanA scan


A scanA scan

B scanB scan

S

i

g

n

a

l

A

m

p

l

i

t

u

d

e

Time

A scanA scan


initial pulse

back surfaceecho

Types of DisplayTypes of Display


plate

crack

0 2 4 6 8 10

crackecho

UT Instrument Screen


1. Normal Probe Transmission MethodNormal Probe Transmission Method

Inspection Techniques


Limitations

Specimen must have parallel sides

Two probes are required

The two probes must be exactly opposite one another

Gives no indication of the depth of the defect


2. Normal Probe Reflection MethodNormal Probe Reflection Method


Advantages

Specimen may be of any shapeSpecimen may be of any shape

Access to only one side of the testAccess to only one side of the test--piece is requiredpiece is required

Only one coupling agent is requiredOnly one coupling agent is required

The distance of the defect from the probe can be measuredThe distance of the defect from the probe can be measured


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Reflective TechniquesReflective Techniques


ASTM Distance/Area Amplitude

ThicknessThickness calibrationcalibration standardsstandards


NAVSHIPS


IIW

DSC DC Rhompas

CalibrationCalibration standardsstandards forfor angleangle probesprobes


SC

ASME Pipe Sec. XI



RADIOGRAPHYRADIOGRAPHY


RadiographyRadiography usesuses differentialdifferential absorptionabsorption ofof radiationradiation (X(X--raysrays andand --rays)rays)whichwhich penetratepenetrate aa testtest--piecepiece toto produceproduce aa recordingrecording ofof anan imageimage onon filmfilmtoto detectdetect featuresfeatures ofof thethe testtest--piecepiece thatthat showshow aa differentdifferent thicknessthickness orordensitydensity asas comparedcompared toto thethe surroundingsurrounding materialmaterial..


WhenWhen passingpassing throughthrough thethe specimen,specimen, aa proportionproportion ofof thethe radiationradiation isisabsorbedabsorbed asas functionfunction ofof thicknessthickness oror densitydensity..

RadiographyRadiography isis capablecapable ofof detectingdetecting anyany featurefeature inin aa componentcomponentprovidedprovided thatthat therethere areare sufficientsufficient differencesdifferences inin thicknessthickness oror densitydensitywithinwithin thethe partpart..


Features that exhibit a 1% or more Features that exhibit a 1% or more difference in absorptiondifference in absorption compared to compared to the surrounding material can be detected.the surrounding material can be detected.

Radiography is thus used to detect Radiography is thus used to detect internal (subsurface) defectsinternal (subsurface) defects such as such as


Radiography is thus used to detect Radiography is thus used to detect internal (subsurface) defectsinternal (subsurface) defects such as such as porosity and inclusions.porosity and inclusions.


Principles of RadiographyPrinciples of Radiography


Radiation penetrates Radiation penetrates samplesample

Exposure Exposure recording recording devicedevice

SampleSample


1.1. What are XWhat are X--rays?rays?

XX--raysrays areare electromagneticelectromagnetic radiationradiation ofofwavelengthwavelength aboutabout 11 ((1010--1010 m),m), (about(about thethe samesamesizesize asas anan atom)atom)..


TheyThey occuroccur inin thatthat portionportion ofof thethe electromagneticelectromagneticspectrumspectrum betweenbetween --raysrays andand thethe ultravioletultraviolet..

XX--raysrays werewere discovereddiscovered inin 18951895 byby RontgenRontgen andandareare usedused forfor diffractiondiffraction purposespurposes toto studystudy thethecrystalcrystal structurestructure atat thethe atomicatomic levellevel..


Characteristic RadiationCharacteristic RadiationCharacteristic RadiationCharacteristic RadiationCharacteristic RadiationCharacteristic RadiationCharacteristic RadiationCharacteristic Radiation


Continuous Continuous Continuous Continuous Continuous Continuous Continuous Continuous SpectrumSpectrumSpectrumSpectrumSpectrumSpectrumSpectrumSpectrum

Process of the emission of characteristic X-rays.


The best results are obtained when the defect has an appreciable The best results are obtained when the defect has an appreciable thickness in a direction parallel to the radiation beamthickness in a direction parallel to the radiation beam

Plane defects such as cracks are always detectable and the ability to Plane defects such as cracks are always detectable and the ability to locate a crack will depend upon its orientation to the radiation beamlocate a crack will depend upon its orientation to the radiation beam


Radiographic inspection consists of three important elements:Radiographic inspection consists of three important elements:

Source of radiation (XSource of radiation (X--rays or rays or --rays)rays)

Object to be inspectedObject to be inspected

Radiographic filmRadiographic film


XX--rays and rays and --raysrays are similar and the only difference between them is in the way are similar and the only difference between them is in the way they are produced. they are produced.

XX--rays produced by high voltage x ray tubes when a stream of high electrons rays produced by high voltage x ray tubes when a stream of high electrons strike a metal targetstrike a metal target


-- raysrays areare producedproduced fromfrom radioactiveradioactive isotopesisotopes suchsuch asas IridiumIridium 192192.. TheyThey areareemittedemitted fromfrom thethe nucleusnucleus asas partpart ofof thethe decaydecay (desintegration)(desintegration) processprocess ofofradioactiveradioactive elementselements..

TheThe XX--rayray oror --raysrays areare placedplaced closeclose toto thethe materialmaterial toto bebe inspectedinspected andand theytheypasspass throughthrough thethe materialmaterial andand areare thenthen capturedcaptured onon filmfilm.. ThisThis filmfilm isis thenthenprocessedprocessed andand thethe imageimage isis obtainedobtained asas aa seriesseries ofof graygray shadesshades betweenbetween blackblackandand whitewhite..


TheThe choicechoice ofof whichwhich typetype ofof radiationradiation isis usedused (X(X--rayray oror --rays)rays) dependsdepends onon thethethicknessthickness ofof thethe materialmaterial toto bebe testedtested.. -- sourcessources havehave thethe advantageadvantage ofof portabilityportabilitywhichwhich makesmakes themthem idealideal forfor useuse inin constructionconstruction sitesite workingworking..

WhenWhen XX--rayray andand --raysrays passpass throughthrough anyany mediummedium theythey interactinteract withwith thethe atomsatoms ofofthisthis mediummedium.. DuringDuring thisthis process,process, theythey willwill bebe attenuatedattenuated (absorbed)(absorbed) inin somesome wayway..


TheThe imageimage ofof defectsdefects whichwhich projectsprojects ontoonto thethe recordingrecording filmfilm isis thethe resultsresults ofofdifferencesdifferences inin thethe attenuationattenuation ratesrates oror absorptionabsorption ratesrates..

TheThe degreedegree ofof attenuationattenuation isis affectedaffected byby severalseveral factorsfactors::

DensityDensity

StructureStructure ofof thethe mediummedium (specimen)(specimen)

Type,Type, intensityintensity andand energyenergy ofof radiationradiation usedused


The intensity of radiation which emerges from the specimen decreases The intensity of radiation which emerges from the specimen decreases exponentially with its thickness:exponentially with its thickness:

IIxx = I= Ioo ee--tt


The The accurate reproduction of a recognizable imageaccurate reproduction of a recognizable image is a primary is a primary requirement for radiography. requirement for radiography.

This is dependent on several factors but the most important is the This is dependent on several factors but the most important is the difference in radiation intensity on the various parts of the imagedifference in radiation intensity on the various parts of the image


TheThe qualityquality ofof aa radiographradiograph (image)(image) dependsdepends onon::

ContrastContrast

DefinitionDefinition ((clearnessclearness andand sharpness)sharpness)

XX--raysrays andand gammagamma raysrays areare veryvery hazardoushazardous.. SpecialSpecial precautionsprecautions mustmust


XX--raysrays andand gammagamma raysrays areare veryvery hazardoushazardous.. SpecialSpecial precautionsprecautions mustmustbebe takentaken whenwhen performingperforming radiographyradiography..

ThereforeTherefore thethe operatoroperator willwill useuse thesethese insideinside aa protectiveprotective enclosureenclosure ororwithwith appropriateappropriate barriersbarriers andand warningwarning signalssignals toto ensureensure therethere areare nonohazardshazards toto personnelpersonnel


EDDY CURRENT TESTINGEDDY CURRENT TESTING


EDDY CURRENT TESTINGEDDY CURRENT TESTING


EddyEddy currentcurrent testingtesting isis anan electromagneticelectromagnetic techniquetechnique andand cancan onlyonly bebeusedused onon conductiveconductive materialsmaterials

EddyEddy currentcurrent inspectioninspection cancan bebe suedsued toto detectdetect surfacesurface andand internalinternaldefectsdefects withinwithin componentscomponents..


ItIt cancan alsoalso determinedetermine thicknessthickness ofof surfacesurface coating,coating, provideprovide informationinformationonon graingrain sizesize andand heatheat treatmenttreatment conditioncondition andand alsoalso measuremeasure electricalelectricalandand magneticmagnetic conductivitiesconductivities..

WhenWhen anan alternatingalternating currentcurrent (AC)(AC) isis passedpassed throughthrough aa coilcoil (conducting(conductingmaterial)material) aa magneticmagnetic fieldfield isis generatedgenerated..


IfIf thisthis coilcoil isis placedplaced nearnear aa conductiveconductive materialmaterial (specimen),(specimen), thethemagneticmagnetic fieldfield causescauses eddyeddy currentscurrents toto flowflow..

TheThe inducedinduced eddyeddy currentscurrents willwill produceproduce aa magneticmagnetic fieldfield inin oppositeoppositedirectiondirection toto thethe primaryprimary magneticmagnetic fieldfield surroundingsurrounding thethe coilcoil causingcausing aachangechange inin thethe impedanceimpedance valuevalue ofof thethe coilcoil..


changechange inin thethe impedanceimpedance valuevalue ofof thethe coilcoil..

EddyEddy currentscurrents areare affectedaffected byby thethe physicalphysical andand electricalelectrical propertiesproperties ofofthethe materialmaterial..

AnAn eddyeddy currentcurrent instrumentinstrument sensessenses thethe resultingresulting changeschanges inin thethe coilscoilsimpedanceimpedance andand displaysdisplays thesethese changeschanges inin aa mannermanner thatthat allowsallows thetheinspectorinspector toto obtainobtain informationinformation aboutabout thethe propertiesproperties andand conditioncondition ofof thethematerialmaterial


IfIf aa materialmaterial isis uniformuniform inin compositioncomposition andand dimensionsdimensions thethe impedanceimpedancevaluevalue ofof thethe coilcoil closeclose toto thethe specimenspecimen surfacesurface willwill bebe thethe samesame..

IfIf thethe specimenspecimen containscontains aa defectdefect oror therethere areare materialmaterial variations,variations, thetheeddyeddy currentscurrents inin thethe specimenspecimen willwill bebe distorteddistorted byby thesethese defectsdefects andand thetheimpedanceimpedance inin thethe coilcoil isis changedchanged


impedanceimpedance inin thethe coilcoil isis changedchanged

ThisThis changechange inin impedanceimpedance valuevalue isis measuredmeasured andand displayeddisplayed inin aamannermanner thatthat indicatesindicates thethe typetype ofof flawflaw oror materialmaterial conditioncondition..

TheThe factorsfactors thatthat affectaffect impedanceimpedance valuevalue areare mainlymainly:: dimensionsdimensions ofof testtest--piece,piece, conductivityconductivity,, magneticmagnetic permeabilitypermeability andand presencepresence ofof anyany defectsdefects


Principles of Eddy CurrentPrinciples of Eddy Current:

Presence of cracks can cause disruption in the circular flow pattern of the eddy current, causing a change in properties


Magnetic Field

From Test Coil

Magnetic Field

From

Eddy Currents

Eddy Currents

Crack


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Inspection ProbesInspection Probes

SingleSingle CoilCoil ProbeProbe:: DetectDetect surfacesurface defectsdefects suchsuch asas crackscracks..

TheThe probeprobe shouldshould bebe heldheld normalnormal toto thethe componentcomponent surfacesurface

TwinTwin CoilCoil ProbeProbe:: SuitableSuitable forfor measurementmeasurement ofof thicknessthickness ofof surfacesurfacecoatingcoating oror forfor conductivityconductivity measurementmeasurement



PhasePhase AnalysisAnalysis

PhasePhase analysisanalysis isis usedused toto representrepresent thethe signalssignals fromfrom eddyeddy currentcurrentinspectioninspection..

WhenWhen itit isis necessarynecessary toto detectdetect changeschanges inin oneone parameterparameter affectingaffecting thethe


WhenWhen itit isis necessarynecessary toto detectdetect changeschanges inin oneone parameterparameter affectingaffecting thetheimpedanceimpedance valuevalue andand allall otherother factorsfactors areare constant,constant, thenthen thethemeasurementmeasurement ofof thethe changechange inin impedanceimpedance valuevalue willwill reflectreflect aa changechange ininthisthis parameterparameter..

However,However, therethere areare casescases wherewhere moremore thanthan oneone parameterparameter affectaffect thetheimpedanceimpedance value,value, andand wewe needneed toto separateseparate thethe responsesresponses fromfrom allallthesethese parametersparameters


Display MethodsDisplay Methods

There are two main methods used to display the impedance value on a There are two main methods used to display the impedance value on a screenscreen

11.. VectorVector MethodMethod


AA spotspot isis projectedprojected ontoonto thethe screen,screen, representingrepresenting thethe impedanceimpedance ZZoo..

WhenWhen thethe coilcoil isis placedplaced nearnear thethe testtest--piecepiece thethe spotspot willwill movemove toto correspondcorrespondwithwith thethe impedanceimpedance changechange ZZ11..

ThisThis positionposition forfor aa referencereference testtest blockblock cancan bebe adjustedadjusted toto bebe atat centrecentre forforexampleexample..

AnyAny variationvariation oror presencepresence ofof defectdefect inin thethe testtest--piecepiece willwill causecause aa movementmovementofof thethe spotspot andand thethe directiondirection ofof thisthis movementmovement willwill indicateindicate thethe causecause ofofvariationvariation..


Vector MethodVector Method



2.2. Ellipse MethodEllipse Method

ThisThis methodmethod isis usuallyusually usedused whenwhen thethe twintwin coilcoil probeprobe isis employedemployed..

WhenWhen thethe probeprobe coilcoil inin positionposition withwith aa referencereference block,block, thethe screenscreen displaydisplay


WhenWhen thethe probeprobe coilcoil inin positionposition withwith aa referencereference block,block, thethe screenscreen displaydisplayisis aa setset asas aa horizontalhorizontal lineline..

AA variationvariation inin oneone variablevariable cancan bebe denoteddenoted byby aa changechange inin thethe angleangle ofof thethelineline andand aa secondsecond variablevariable cancan bebe bebe denoteddenoted byby thethe formationformation ofof ananellipseellipse..

TheThe valuesvalues ofof bothboth parametersparameters cancan bebe determineddetermined byby analysinganalysing bothboth thethepositionposition andand shapeshape ofof thethe ellipseellipse


Ellipse MethodEllipse Method


Change in 1Change in 1stst parameterparameter

Reference lineReference line Change in 2Change in 2ndnd parameterparameter

Change in both parametersChange in both parameters


Examples of Eddy Current ApplicationsExamples of Eddy Current Applications


Eddy current use to detect corrosion and Eddy current use to detect corrosion and erosion in aerospace and power generation erosion in aerospace and power generation www.ndt-ed.org


Eddy Current Instrumentation Eddy Current Instrumentation



Flaw Type

Inspection Method

Visual

InspectionLPI MPI

UT

(Straight probe)

UT

(Angle probe)EC RAD

Surface breaking

linear1 3 3 1 2 3 1

Surface breaking,

volumetric3 3 3 3 3 3 3

Near surface, linear &

normal to surface0 0 2 1 2 3 1


normal to surface

Near surface linear &


Near surface,

volumetric0 0 2 3 3 3 3

Subsurface, linear &


Subsurface, linear &

parallel to surface0 0 0 3 3 0 1

Subsurface, volumetric 0 0 0 3 3 0 3

(0) will not detect, (1) not well suited, (2) fairly well suited, (3) ideal application


LPI MPI UT EC Radiography

Principles


PrinciplesPenetrant is applied to the surface of a pre-cleaned component. The liquid is pulled into surface-breaking defects by capillary action. Excess penetrant material is removed from the surface. A developer is applied to pull the trapped penetrant back to the surface where it is spread out and forms an indication. The indication is much easier to see than the actual defect.

A component made from ferromagnetic material is magnetised. The magnetic lines of force travel through the material, and exit and re-enter the material at the poles. Defects such as crack or voids cannot support as much flux, and force some of the flux outside of the part. Magnetic particles distributed over the component will be attracted to areas of flux leakage and produce a visible indication.

High frequency sound waves are sent into a material by use of a transducer. The sound waves travel through the material and are received by the same transducer or a second transducer. The amount of energy transmitted or received and the time the energy is received are analyzed to determine the presence of flaws.

AC current is passed through a coil producing a magnetic field. When the coil is placed near a conductive material, the changing magnetic field induces current flow in the material. These currents travel in closed loops and are called eddy currents. Eddy currents produce their own magnetic field that can be measured and used to find flaws and characterize conductivity, permeability, and dimensional features.

X-rays are used to produce images of objects using a film or other detector that is sensitive to radiation. The component is placed b/w the radiation source and detector. Thickness and density of the material that X-rays must penetrate affects the amount of radiation reaching the detector. This variation in radiation produces an image on the detector that shows internal features of the component

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Main Uses


Main Uses

Used to locate cracks, porosity, and other defects that break the surface of a material and have enough volume to trap and hold the penetrant material.

Liquid penetrant testing is used to inspect large areas very efficiently and will work on most non-porous materials

Used to inspect ferromagnetic materials (those that can be magnetized) for defects that result in a transition in the magnetic permeability of a material.

Magnetic particle inspection can detect surface and near surface defects.

Used to locate surface and subsurface defects in many materials including metals, plastics, and wood.

Ultrasonic inspection is also used to measure the thickness of materials and otherwise characterize properties of material based on sound velocity and attenuation measurements.

Used to detect surface and near-surface flaws in conductive materials, such as the metals.

Eddy current inspection is also used to sort materials based on electrical conductivity and magnetic permeability, and measures the thickness of thin sheets of metal and nonconductive coatings such as paint.

Used to inspect almost any material for surface and subsurface defects.

X-rays can also be used to locates and measures internal features, confirm the location of hidden parts in an assembly, and to measure thickness of materials.




Advantages


Advantages

Large surface areas or large volumes of parts/materials can be inspected rapidly and at low cost.Parts with complex geometry are routinely inspected.Indications are produced directly on surface of the part providing a visual image of the discontinuity.Equipment investment is minimal.

Large surface areas of complex parts can be inspected rapidly.Can detect surface and subsurface flaws.Surface preparation is less critical than it is in penetrant inspection.Magnetic particle indications are produced directly on the surface of the part and form an image of the discontinuity.Equipment costs are relatively low.

Depth of penetration for flaw detection or measurement is superior to other methods.Only single sided access is required.Provides distance information.Minimum part preparation is required.Method can be used for much more than just flaw detection.

Detects surface and near surface defects.Test probe does not need to contact the part.Method can be used for more than flaw detection.Minimum part preparation is required.

Can be used to inspect virtually all materials.Detects surface and subsurface defects.Ability to inspect complex shapes and multi-layered structures without disassembly.Minimum part preparation is required.




Limitations


LimitationsDetects only surface breaking defects.Surface preparation is critical as contaminants can mask defects.Requires a relatively smooth and nonporous surface.Post cleaning is necessary to remove chemicals.Requires multiple operations under controlled conditions.Chemical handling precautions are necessary (toxicity, fire, waste).

Only ferromagnetic materials can be inspected.Proper alignment of magnetic field and defect is critical.Large currents are needed for very large parts.Requires relatively smooth surface.Paint or other nonmagnetic coverings adversely affect sensitivity.Demagnetization and post cleaning is usually necessary.

Surface must be accessible to probe and couplantSkill and training required is more extensive than other techniqueSurface finish and roughness can interfere with inspectionThin parts may be difficult to inspect.Linear defects oriented parallel to the sound beam can go undetected.Reference standards are often needed.

Only conductive materials can be inspected.Ferromagnetic materials require special treatment to address magnetic permeability.Depth of penetration is limited.Flaws that lie parallel to the inspection probe coil winding direction can go undetected.Skill and training required is more extensive than other techniques.Surface finish and roughness may interfere..

Extensive operator training and skill required.Access to both sides of the structure is usually required.Orientation of the radiation beam to non-volumetric defects is critical.Field inspection of thick section can be time consuming.Relatively expensive equipment investment is required.Possible radiation hazard for personnel.


NDT_2 [Compatibility Mode].pdf

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