giẢi ĐoÁn & ĐÁnh giÁ-ut

8/7/2019 GII ON & NH GI-UT

1/71

GII ON & NH GIGII ON & NH GI NGUYN TC CHUNGNGUYN TC CHUNG

GII ON V NH GI BNG KGII ON V NH GI BNG K

THUT XUNGTHUT XUNG -- TING VNGTING VNG


2/71

NGUYN TC CHUNGNGUYN TC CHUNG

determinationofbasic ultrasonic parametersdeterminationofbasic ultrasonic parameters(echoheight,timeofflight);(echoheight,timeofflight);

determinationofits basicshapeandorientationdeterminationofits basicshapeandorientation sizing:sizing:

measurementofoneormoredimensions (ormeasurementofoneormoredimensions (or

area/volume), withinthe limitationsofthemethods;area/volume), withinthe limitationsofthemethods; measurementofsomeagreed parametere.g.echomeasurementofsomeagreed parametere.g.echo

heightheight


3/71

NGUYN TC CHUNGNGUYN TC CHUNG

locationdiscontinuitieslocationdiscontinuities

determinationofanyotherparametersordeterminationofanyotherparametersorcharacteristicsthatmay benecessaryforcharacteristicsthatmay benecessaryfor

completeevaluationcompleteevaluation

assessmentofprobablenature,e.g.crackorassessmentofprobablenature,e.g.crackor

inclusioninclusion


4/71

GII ON V NH GI BNGGII ON V NH GI BNG

K THUT XUNGK THUT XUNG -- TING VNGTING VNG Locationofdiscontinuity

Orientationofdiscontinuity Assessmentofmultipleindications

Shapeofdiscontinuity

Maximumechoheightofindication

Sizeofdiscontinuity


5/71

XC NH V TR KHUYT TTXC NH V TR KHUYT TT

reference to the index point and beam anglereference to the index point and beam angle

ofthe probe,ofthe probe,

measurement of the probe position andmeasurement of the probe position and

beam path length at whichbeam path length at which the maximum

echo heightis observed.is observed.


6/71

XC NH HNG KHUYT TTXC NH HNG KHUYT TT

TheorientationofadiscontinuityisthedirectionTheorientationofadiscontinuityisthedirectionorplanealong whichthediscontinuityhasitsorplanealong whichthediscontinuityhasits

majoraxis withrespecttoadatumreferenceonmajoraxis withrespecttoadatumreferenceonthetestobject.thetestobject.

determinedfromobservationofthedeterminedfromobservationofthedifferencebeam angles and/or scanning directions atatwhichthemaximumechoheightisobtainedwhichthemaximumechoheightisobtained

Maynotrequiredinseveral applicationsMaynotrequiredinseveral applications


7/71

NH GI CH TH PHC TPNH GI CH TH PHC TP

ThequalitativedeterminationconsistsofascertainingThequalitativedeterminationconsistsofascertainingwhetherornotsuchindicationscorrespondtooneorwhetherornotsuchindicationscorrespondtooneormoreseparatediscontinuitiesmoreseparatediscontinuities

CH TH BLT PHAN GIITT

CH TH BLT PHN GIIKEM


8/71


determine whethertheechoesarisefromaseriesofdetermine whethertheechoesarisefromaseriesof

closelyspaced butseparatediscontinuities,orfromacloselyspaced butseparatediscontinuities,orfroma

singlecontinuousdiscontinuityhavinganumberofsinglecontinuousdiscontinuityhavinganumberofseparatereflectingfacets, usingthefollowingseparatereflectingfacets, usingthefollowing

techniquestechniques

Lateral/dccharacterisationLateral/dccharacterisation

Transverse/ngang (ThroughTransverse/ngang (Through--thickness)characterisationthickness)characterisation

Shadow technique/K thut bng(truynqua)Shadow technique/K thut bng(truynqua)


9/71


Lateral characterisation

Fordiscontinuitiesshowingasingle,sharp indicationFordiscontinuitiesshowingasingle,sharp indication

Usethenarrowest practical beam widthatthedistanceoftheUsethenarrowest practical beam widthatthedistanceofthediscontinuity,andacareful lateral scan underuniformdiscontinuity,andacareful lateral scan underuniformcouplingconditions.couplingconditions.

notingthattheechoheightfallsrapidlyaboutthenormal andnotingthattheechoheightfallsrapidlyaboutthenormal andthatnosignificantsecondaryechoesareobservedthatnosignificantsecondaryechoesareobserved

dipsintheechoheightenvelopealongits lengthmeansthatdipsintheechoheightenvelopealongits lengthmeansthatthediscontinuityisintermittent Thisshould beconfirmed bythediscontinuityisintermittent Thisshould beconfirmed bycarryingoutswivel andorbital scansadjacenttotheapparentcarryingoutswivel andorbital scansadjacenttotheapparentbreaksbreaks


10/71


Transverse (throughTransverse (through--thickness) characterisationthickness) characterisation

Careful transversescansacrossthediscontinuityfromat leastCareful transversescansacrossthediscontinuityfromat least

twodirectionsatshortsound pathrangestwodirectionsatshortsound pathranges

Theformoftheechoenvelopeshall benoted (nghincuTheformoftheechoenvelopeshall benoted (nghincu

sau)sau)

Significantdipsorcomplete breaksintheechoenvelopeSignificantdipsorcomplete breaksintheechoenvelope

suggestthatthediscontinuitymay beintermittentsuggestthatthediscontinuitymay beintermittent Whereaccess permits,acompositethroughWhereaccess permits,acompositethrough--thickness picturethickness picture

ofthediscontinuitymay be built up by plottingall theechoesofthediscontinuitymay be built up by plottingall theechoes

observedfromanumberofdifferentdirectionsandangles.observedfromanumberofdifferentdirectionsandangles.


11/71


Shadow techniqueShadow technique

1: Transmissionsignal1: Transmissionsignal2: A2: A--scanscan

3: Intermittentdiscontinuity3: Intermittentdiscontinuity

4: Notransmittedsignal4: Notransmittedsignal

5: Continuousdiscontinuity5: Continuousdiscontinuity


12/71


Shadow technique

Useful whenthedimensionsofthediscontinuity,orgroup ofUseful whenthedimensionsofthediscontinuity,orgroup of

discontinuities,areapproximatelyequal tothe beam width.discontinuities,areapproximatelyequal tothe beam width. A strongtransmittedsignal throughtheaffectedareais positiveA strongtransmittedsignal throughtheaffectedareais positive

proofoftheabsenceofamajordiscontinuity. Theamplitudeofproofoftheabsenceofamajordiscontinuity. Theamplitudeofthetransmittedsignal is linkedtotheratioofthediscontinuitythetransmittedsignal is linkedtotheratioofthediscontinuity

areatothe beamarea.areatothe beamarea. SincethethroughSincethethrough--thicknessdimensionofadiscontinuityisthicknessdimensionofadiscontinuityis

generallyofcritical importance,itshould beassumedto begenerallyofcritical importance,itshould beassumedto becontinuous unlessthereisconclusiveevidencethatitiscontinuous unlessthereisconclusiveevidencethatitisintermittentinthisdirectionintermittentinthisdirection


13/71

XC NH HNH DNG KHUYT TTXC NH HNH DNG KHUYT TT

Discontinuity is classified to:

Point- nosignificantextentinanydirection;

Elongated- asignificantextentinonedirection

Complex- asignificantextentinmorethanone

directionandmay besub-dividedinto: PlanarPlanar-- asignificantextentin 2 directionsonlyasignificantextentin 2 directionsonly

VolumetricVolumetric-- asignificantextentin3directions.asignificantextentin3directions.


14/71


Requirements of the acceptance standard:

separateacceptancecriteriaforeachofthe

discontinuity

thediscontinuityis projectedononeormore pre-

establishedsections,andeach projectionisconservativelytreatedasacrack-like planar

discontinuity


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16/71


Assess extentofofthe discontinuity

Reconstructiontechnique

Echoenvelopetechnique


17/71


Reconstruction technique:Reconstruction technique: ForeachForeach

scanningmovement,animageofthescanningmovement,animageofthe

discontinuityisreconstructed by plottingaseriesdiscontinuityisreconstructed by plottingaseries

ofindicationsfromthediscontinuityoverwhichofindicationsfromthediscontinuityoverwhich

theechoheightexceedstheevaluation/recordingtheechoheightexceedstheevaluation/recording

level.level.


18/71


Echo envelope technique:Echo envelope technique: Foreachscanningmovement,theshapeofindicationfromdiscontinuitiesanditsvariationinechoheightisobserved.A singlesharp indicationthatrisessmoothlytoaA singlesharp indicationthatrisessmoothlytoa

maximumamplitude beforefallingsmoothlytothemaximumamplitude beforefallingsmoothlytothebase line,isclassifiedashavingnosignificantextent.base line,isclassifiedashavingnosignificantextent.

All othertypesofindication,e.g.multiple peaksorAll othertypesofindication,e.g.multiple peaksorirregularvariationinechoheight,areconsideredtoirregularvariationinechoheight,areconsideredtobecharacteristicofdiscontinuities withasignificantbecharacteristicofdiscontinuities withasignificantextent.extent.


19/71


Echodynamic pattern technique

Theechodynamic patternofadiscontinuityistheTheechodynamic patternofadiscontinuityisthe

changeinshapeandamplitudeofitsecho whenanchangeinshapeandamplitudeofitsecho whenan

ultrasonic beamistraversedacrossit.ultrasonic beamistraversedacrossit.

Discontinuitiesshould bescanned, witheach probe,inDiscontinuitiesshould bescanned, witheach probe,in

twomutually perpendiculardirections,i.e. bothalongtwomutually perpendiculardirections,i.e. bothalongandacrossthediscontinuity,andthe patternineachandacrossthediscontinuity,andthe patternineach

directionshould benoted.directionshould benoted.


20/71


Scanning directions:Scanning directions:

1. Discontinuity2. Scanningdirections1

3. Probemovement

4. Scanningdirections 2


21/71


Scanningfrom additionaldirections and withScanningfrom additionaldirections and with

otherprobes willgive useful additionalotherprobes willgive useful additional

information.information.

There are 4 typicalecho responses of theThere are 4 typicalecho responses of the

different types ofdiscontinuities.different types ofdiscontinuities.


22/71


PATTERN 1 RESPONSEPATTERN 1 RESPONSE

1: Amplitude1: Amplitude

2 : A scan2 : A scan

3: Range3: Range4: Variationin peaksignal amplitude4: Variationin peaksignal amplitude

5 : Probe position5 : Probe position

6: Reflector6: Reflector

7:Weld7:Weld

8: Typical occurrencein8: Typical occurrencein

thoughthough-- thicknessdirectionthicknessdirection


lateral (length)directionlateral (length)direction


23/71


Pattern 1:Pattern 1:

Asthe probeismoved,indicationrisesinamplitudesmoothlyto

asinglemaximum beforefallingsmoothlytonoise level. EchoEcho--dynamic pattern1isasinglereflectingsurfaceinthedynamic pattern1isasinglereflectingsurfaceinthe

directionalong whichthe ultrasonic beamistraversed.directionalong whichthe ultrasonic beamistraversed.

EchoEcho--dynamic pattern1oncurvedsurface (i.e.spherical ordynamic pattern1oncurvedsurface (i.e.spherical or

cylindrical)may beflat,andeithersmoothorroughcylindrical)may beflat,andeithersmoothorrough

EchoEcho--dynamic pattern1ontoosmall curvedsurfacemaydynamic pattern1ontoosmall curvedsurfacemay

produceeithera pattern 2 responseora pattern3response.produceeithera pattern 2 responseora pattern3response.


24/71













25/71



Showsasinglesharp echo aatany probe position

Whenthe ultrasonic beamismovedoverthediscontinuitytheWhenthe ultrasonic beamismovedoverthediscontinuitytheechorisessmoothlytoa plateau andismaintained until the beamechorisessmoothlytoa plateau andismaintained until the beam

movesoffthediscontinuity, whentheecho will fall smoothlytomovesoffthediscontinuity, whentheecho will fall smoothlyto

noise level.noise level.

Pattern 2 isindicativeofa largerreflectingsurface,equal toorPattern 2 isindicativeofa largerreflectingsurface,equal toorgreaterthantheapproximate6dB beam width,and lyinggreaterthantheapproximate6dB beam width,and lying

approximately perpendiculartothe beamaxisinthedirectionapproximately perpendiculartothe beamaxisinthedirection

beingscannedbeingscanned


26/71



Pattern3isindicativeofaroughorirregularlyshaped

discontinuity (suchasa largeroughsuchasa largerough--surfacedcrack)surfacedcrack) whichconsistsofanumberofdiscretereflectingfacets.

Animportantcharacteristicofpattern3isthateachAnimportantcharacteristicofpattern3isthateach

individual peakwithintheoverall echoreachesitsindividual peakwithintheoverall echoreachesits

maximumheightinsequence,givingrisetoa "rollingecho"maximumheightinsequence,givingrisetoa "rollingecho"

Therearetwovariantsofpattern3,depending uponthe

angleofincidenceofthe probe beamonthediscontinuity


27/71


PATTERN 3A RESPONSE (NormalPATTERN 3A RESPONSE (Normal

to the discontinuity)to the discontinuity)


2 : A scan2 : A scan3: Range3: Range

4: Variationin peaksignal amplitude4: Variationin peaksignal amplitude








28/71


Pattern 3a:Pattern 3a:

Pattern3aisvalid wheneitherbyanormal beamoranPattern3aisvalid wheneitherbyanormal beamoran

inclined beamhit perpendicularlythediscontinuity.inclined beamhit perpendicularlythediscontinuity.

Showsasingle butraggedechoatany probe positionShowsasingle butraggedechoatany probe position

Asthe probeismovedthismay undergo large (>Asthe probeismovedthismay undergo large (>6dB)6dB)randomfluctuationsinamplituderandomfluctuationsinamplitude


29/71


PATTERN 3B RESPONSE (ObliquePATTERN 3B RESPONSE (Oblique

to the discontinuity)to the discontinuity)



3: Pulseenvelope3: Pulseenvelope

4: Range4: Range

5 : Variationin peaksignal amplitude5 : Variationin peaksignal amplitude

6: Probe position6: Probe position

7: Reflector7: Reflector8: Reflectoe withthrough8: Reflectoe withthrough--thicknessextentthicknessextent






30/71


Pattern 3b:Pattern 3b:

Whenthediscontinuityis beenhit withobliqueincidence,then

the "travellingecho pattern" 3Bisvalid.

Showsanextendedtrainofsignals ("subsidiary peaks") withinaShowsanextendedtrainofsignals ("subsidiary peaks") withina

bellbell--shaped pulseenvelopeatany probe position.shaped pulseenvelopeatany probe position.

Asthe probeismoved,eachsubsidiary peaktravelsthroughtheAsthe probeismoved,eachsubsidiary peaktravelsthroughthe

pulseenvelope,risingtoitsownmaximumtowardsthecentreofpulseenvelope,risingtoitsownmaximumtowardsthecentreoftheenvelope,andthenfalling.theenvelope,andthenfalling.

Theoverall signal mayshow large (>Theoverall signal mayshow large (> 6dB)randomfluctuations6dB)randomfluctuations

inamplitudeinamplitude


31/71






5 : Shortrangeechoes5 : Shortrangeechoes

6: Shortrangeechoes6: Shortrangeechoes

7: Probe position7: Probe position8: Typical occurrence8: Typical occurrence


32/71



Pattern4isindicativeofaclusterofsmall,randomlyPattern4isindicativeofaclusterofsmall,randomly

distributedreflectors,anddiffersfrom pattern3innotdistributedreflectors,anddiffersfrom pattern3innot

showingthe "rollingecho" effect.showingthe "rollingecho" effect.

Showsaclusterofsignals whichmayormaynot be wellShowsaclusterofsignals whichmayormaynot be well

resolvedinrangeatany probe positionresolvedinrangeatany probe position

Asthe probeismoved,thesignalsriseandfall atrandomAsthe probeismoved,thesignalsriseandfall atrandom

butthesignal fromeachseparatediscontinuityelement,ifbutthesignal fromeachseparatediscontinuityelement,if

resolved,shows pattern1response.resolved,shows pattern1response.


33/71

XC NH HNG KHUYT TTXC NH HNG KHUYT TT

Theechoheightfromadiscontinuitydepends uponitssize,Theechoheightfromadiscontinuitydepends uponitssize,orientationandsurfacecontour.Bymeasuringtheechoheightorientationandsurfacecontour.Bymeasuringtheechoheightfromdifferentdirectionsandangles,itis possibletoobtainfromdifferentdirectionsandangles,itis possibletoobtain

informationaboutthesecharacteristics.informationaboutthesecharacteristics. A flaw whichshowsrelativelyconstantechoheightsovera wideA flaw whichshowsrelativelyconstantechoheightsovera wide

rangeofincidentangles (low directional reflectivity)is likelytorangeofincidentangles (low directional reflectivity)is likelytobesphericalbespherical

A discontinuity whichshowsaveryhighdifferenceinechoA discontinuity whichshowsaveryhighdifferenceinechoheightsovera widerangeofincidentangles (highdirectionalheightsovera widerangeofincidentangles (highdirectionalreflectivity) is likelyto bea largesmoothreflectorlyingreflectivity) is likelyto bea largesmoothreflectorlyingperpendiculartothe beamangleat whichthemaximumechoperpendiculartothe beamangleat whichthemaximumechoheight wasobserved.height wasobserved.


34/71

TNG HP DLIUTNG HP DLIU


35/71

CHN PHNG PHP NH GI

L

N KHUYT TT maximumechoheighttechniquesmay beappliedonlyifthedimensionto bemeasuredis lessthanthe6dB beam widthoftheprobe

fixedamplitude level techniquesmay beappliedtodiscontinuitiesofanydimension, butsincethemeasuredsizeisanarbitraryvaluedependentonthe particularamplitude levelselected,thesetechniquesshouldonly be used whenspecificallycalledforintheacceptancestandard

techniques basedon probemovementataspecifieddBdropbelow themaximumechoheightfromthe particulardiscontinuitymay beappliedonly wherethemeasureddimensionisgreaterthanthe beam widthatthesamedBdrop. Ifthisconditionisnotfulfilled,thedimensionofthediscontinuityshall beassumedtobeequal totheapplicable beam width


36/71

CHN PHNG PHP NH

GI L

N KHUYT TT(TT) techniques basedon positioningtheindividual edgesof

adiscontinuitycanonly beapplied whenthe ultrasonic

indicationfromthediscontinuityshowstwoormoreresolvableechomaxima;

ifthedimensionto bedeterminedismeasured bymore

thanoneabove-mentionedtechnique,thatvalue

measured bythetechnique whosereliabilityand

accuracycan bedemonstratedto bethehighestshall be

assumedto becorrect.


37/71

NH GI LN KHUYT TTNH GI LN KHUYT TT

Maximumechoheightsizingtechnique

Probemovementsizingtechniques


38/71

K THUT CHIU CAO XUNG CC IK THUT CHIU CAO XUNG CC I

based on a comparison of the maximum echo heightfromadiscontinuity withtheechoheightfromareferencereflectoratthesamesound pathrange.Theyareonlymeaningful if:

theshapeandorientationofthediscontinuityarefavourableforreflection,hencetheneedtotakeechoheightmeasurementsfromseveral directionsorangles, unlesstheshapeandorientationarealreadyknown;and

thedimensionsofthediscontinuity, perpendiculartothe beamaxis,are lessthanthe beam widthineitheroneorbothdirections;

the basicshapeandorientationofthereferencetargetaresimilartothoseofthediscontinuityto beevaluated.

referencetargetmay beeitheradiscshapedreflector,e.g.flat-bottomedholeoranelongatedreflector,e.g.asidedrilledholeor

notch.


39/71

K THUT CHIU CAO XUNG CC IK THUT CHIU CAO XUNG CC I

Distance-gain-size (DGS) technique fordiscontinuities

whosereflectiveareahasdimensions lessthanthe beam

widthinall directions Distance-amplitude-correction (DAC) curve technique

fordiscontinuities whosereflectiveareashowsa

narrow,elongatedform,i.e.havinga lengthgreaterthanthe beam widthandatransversedimension lessthanthe

beam width.


40/71

K THUT DNG DGSK THUT DNG DGS

DGS curvesshowingtherelationship betweenechoheight,rangeandreflectordiameteraregenerallydeterminedtheoreticallyfora particularprobetype,transducerdiameter,and ultrasonicfrequency

Themaximumechoheightfromadiscontinuityisexpressedintermsoftheequivalentdiameterofacirculardiscreflectorperpendiculartothe beamaxisandatthesamesound pathrangeasthediscontinuity

beingmeasured. Whenapplyinga DGS diagram,anallowancehasto bemadefortheeffectsonechoheightofdifferencesinattenuationandtransferloss betweenthetestobjectunderexaminationandthecalibration block


41/71


Thesmallerandsmootherthediscontinuity,andthemorenearly perpendicularitistothe beamaxis,themoreaccuratethemeasuredequivalentsize will be

Whentestingat longranges,thistechniquehastheadvantageoverthe DAC techniquethat largecalibration blocksarenotrequired;

Its range of application: fromtheendofthenearfieldasfarinthematerial asthediscontinuitysignalscan bedistinguishedfromthenoise level.


42/71


Thegeometryofthetestobject underexamination,orofasuitablyrepresentative

sampleofmaterial,should providea backwallecho whichcan be usedtodeterminematerialattenuationandtransferloss;

Sincetheechoheightfromareflectorisfrequencydependent,onlynarrow band widthprobesshould be used.


43/71

K THUT DNG DACK THUT DNG DAC

PrinciplePrinciple

A DAC curve,showingtherelationship betweenechoheightandA DAC curve,showingtherelationship betweenechoheightandrange,isdeterminedexperimentallyfortheactual probeto berange,isdeterminedexperimentallyfortheactual probeto be

usedforevaluationusedforevaluation

Thereferencetargetsmay besideThereferencetargetsmay beside--drilledholes,flatdrilledholes,flat--bottomedbottomedholes,orothershapes,e.g.squareorVholes,orothershapes,e.g.squareorV--shapednotches, whenshapednotches, when

specifiedspecified

ThemaximumechoheightfromadiscontinuityintermsoftheThemaximumechoheightfromadiscontinuityintermsofthenumberofdBitisaboveorbelow theechofromareferencenumberofdBitisaboveorbelow theechofromareferencetargetatthesamerangetargetatthesamerange


44/71


Applications and limitations

Therangeoverwhichthetechniquemay beapplied

depends uponthetypeofreferencetarget.When usingflat-bottomedholesorothersmall reflectors,the

techniquecanonly be usedoutsidethenearzone.When

usingelongatedtargets,e.g.side-drilledholes,thetechniquecanalso be used withinthenearzone


45/71


Applications and limitations (con.)

Echofromthediscontinuityto besizedshall be

maximized DAC curveshall be plottedforthe probeto be used;

When usingacalibration block,asdistinctfromarepresentativesampleofmaterial,thegeometryofthetestobject underexaminationshould providea back-wall echoforthedeterminationofattenuationandtransferloss


46/71

K THUT DI CHUYN U DK THUT DI CHUYN U D

Three sizing techniques categories:

fixed amplitude level techniques wheretheendsofadiscontinuityaretakentocorrespondtothe plotted positionsat whichtheecho

heightfalls below anagreedassessment level; techniques where the edges of the discontinuity are taken to

correspondtothe plotted positionsat whichthemaximumechoheightatany positionalongthediscontinuityhasfallen byanagreednumberofdB. Theedgesofthediscontinuitymay beplottedalongthe beamaxisoralonga pre-determined beamedge;

techniques which aim to position the individual echoes from the

tips of the discontinuity,orfromreflectingfacetsimmediatelyadjacenttotheedges.


47/71


Fixed amplitude level techniquesFixed amplitude level techniques

6 dB dropfrommaximum technique6 dB dropfrommaximum technique

12 dB or 20 dB dropfrommaximum12 dB or 20 dB dropfrommaximumtechniquetechnique

Drop tonoise level techniqueDrop tonoise level technique

6 dB drop tiplocation technique6 dB drop tiplocation technique

Beamaxis tiplocation techniqueBeamaxis tiplocation technique



48/71



Thetechniquemeasuresthedimensionsofa

discontinuityoverwhichtheechoisequal toorgreaterthananagreedamplitudeassessment level. Theamplitude level may berelatedtoa DGS curveormaybeatsomedB level inrelationtoa DAC curve

The beamisscannedoverthediscontinuityandtheprobe positionand beam pathrange,at whichtheechohasfallentotheassessment level,isnoted.


49/71



The position of theedge of thediscontinuity is

thendetermined by plotting the indicatedrange

along the beam axis (using a level of6 dB below a

calibration DAC curve), oralong the 12 dB or20

dB beam edge (using 12 or20 dB drop method)


50/71


Fixed amplitude level techniques using the beamaxisFixed amplitude level techniques using the beamaxis

A : LateralmovementA : Lateralmovement

B : Transverse movementB : Transverse movement

C :C : Calibration curveCalibration curve

D : Assessment levelD : Assessment levelE : Max. echoE : Max. echo


51/71


Fixed amplitude level techniques using the beam edgeFixed amplitude level techniques using the beam edge



C :C : ,, -- beam width atbeam width at

12dB (12dB drop)12dB (12dB drop)


D : Max. echoD : Max. echo

E : Calibration curveE : Calibration curve

F : 12 (or 20) dBF : 12 (or 20) dB


52/71



Simpletoapplyandgiveshighlyreproduciblevalues;

ThemeasuredsizedependsontheamplitudeassessmentThemeasuredsizedependsontheamplitudeassessmentlevellevel

May beappliedto largeorsmall discontinuities but,intheMay beappliedto largeorsmall discontinuities but,inthelattercase,themeasured lengthismorecloselyrelatedtolattercase,themeasured lengthismorecloselyrelatedto

the beam widththantotheactual discontinuitysize;the beam widththantotheactual discontinuitysize; Theassessment level must besetequal toorbelow theTheassessment level must besetequal toorbelow the

amplitude level at whichadiscontinuityofinfinite lengthisamplitude level at whichadiscontinuityofinfinite lengthisacceptable.acceptable.


53/71


6dB drop from maximum technique

Tomakeameasurementthemaximumechoheightis

firstmeasuredandthenthe beamisscannedoverthediscontinuity until theechohasfallen by6dB below

thismaximum.

The positionofthe probeandthesound pathrangearenoted,andtheedgeofthediscontinuityis plottedalong

the beamaxis.


54/71



A :Lateral movement

B: Transversemovement

C :Max.echo


55/71



Onlyapplicable wherethedimensionofthediscontinuityisat

leastequal tothe6dB beam widthattherelevantsound path

range

Wherethediscontinuityis perpendiculartothe beamaxis, whereWherethediscontinuityis perpendiculartothe beamaxis, where

itssurfaceissmooth,and whereitscrossitssurfaceissmooth,and whereitscross-- sectionisequal toorsectionisequal toor

greaterthanthe beam,thetechniquecan be usedtosizing withagreaterthanthe beam,thetechniquecan be usedtosizing witharelativelyhighdegreeofaccuracy.relativelyhighdegreeofaccuracy.

IfthediscontinuityisirregularorofvaryingcrossIfthediscontinuityisirregularorofvaryingcross--section,section,

significantsizingerrorsmayoccursignificantsizingerrorsmayoccur


56/71


12 or 20 dB drop from maximum technique

Theamplitudeassessment level issetateither12 dBor

20dB below themaximumechoheightobservedatanypositionalongthediscontinuity.

Themaximumechoheightfromany positionalongthediscontinuityisnotedandthe beamscannedoverituntil theechoheightfalls byeither12 dBor20dB. Itmeanstheedgeofthediscontinuityis positionedalongthe beamedgeinsteadofthe beamaxis


57/71


12 or 20 dB dropfrommaximum technique12 or 20 dB dropfrommaximum technique



C :C : ,, -- beam width atbeam width at



D : Max. echoD : Max. echo

E : 12 (or 20) dBE : 12 (or 20) dB


58/71


12 or 20 dB drop from maximum technique12 or 20 dB drop from maximum technique

Ifthediscontinuityis perpendiculartothe beamaxis,theIfthediscontinuityis perpendiculartothe beamaxis,the

techniquecan be usedtodetermineitsabsolutedimensions.techniquecan be usedtodetermineitsabsolutedimensions. thetechniqueis potentiallymoreaccuratethanthe6dBdropthetechniqueis potentiallymoreaccuratethanthe6dBdrop

technique buttheneedto plotaccuratelythe beamedges beforetechnique buttheneedto plotaccuratelythe beamedges before

takinganymeasurementscanintroduceanothersourceoftakinganymeasurementscanintroduceanothersourceof

possiblesizingerrorpossiblesizingerror thetechniqueisonlyapplicable wherethedimensionofthethetechniqueisonlyapplicable wherethedimensionofthe

discontinuityto bemeasuredisat leastequal tothediscontinuityto bemeasuredisat leastequal tothe12 dBor12 dBor--2020

dB beam widthatthediscontinuitydistancedB beam widthatthediscontinuitydistance


59/71


Drop to noise level techniqueDrop to noise level technique

A : ProbemovementA : ProbemovementB:Max.echoB:Max.echo

C : Noise levelC : Noise level


60/71



Toapplythetechnique,the ultrasonic beamisscannedToapplythetechnique,the ultrasonic beamisscanned

overthediscontinuityandthe probe positionand beamoverthediscontinuityandthe probe positionand beampathrangenotedat whichthepathrangenotedat whichtheindication is only justindication is only just

discernable above the noise leveldiscernable above the noise level..

Theedgeofthediscontinuityisthen plottedalongtheTheedgeofthediscontinuityisthen plottedalongthebeamaxisbeamaxis


61/71



Thetechniqueisnotveryreproducible. However,itisThetechniqueisnotveryreproducible. However,itisuseful fordeterminingtheoverall sizeofauseful fordeterminingtheoverall sizeofa

discontinuity,orgroup ofdiscontinuities,especiallydiscontinuity,orgroup ofdiscontinuities,especiallywhenthenoise level ishighinrelationtotheechoeswhenthenoise level ishighinrelationtotheechoesfromthediscontinuityfromthediscontinuity

Thetechniquegivesaconservativesizemeasurement,Thetechniquegivesaconservativesizemeasurement,

especially whereothertechniquesespecially whereothertechniquesmay carry the risk ofmay carry the risk ofundersizingundersizinga particulardiscontinuitya particulardiscontinuity

ThetechniqueisrelativelysimpletoapplyanddoesnotThetechniqueisrelativelysimpletoapplyanddoesnotrequirea particularamplitude level to beset.requirea particularamplitude level to beset.


62/71



1:Measuredreflectorlength1:Measuredreflectorlength

2 : Variationin peak2 : Variationin peak

signal amlpitudesignal amlpitude

3: Reflector3: Reflector4: Directionofprobemovement4: Directionofprobemovement

5 : A5 : A -- scanscan


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6dB drop tip location technique6dB drop tip location technique

Thistechniquediffersfromthe6dBdrop techniqueinThistechniquediffersfromthe6dBdrop techniqueinthattheechoheight local toeachendofthethattheechoheight local toeachendofthediscontinuityistakenasthereferencevalueon whichdiscontinuityistakenasthereferencevalueon whichthe6dBdrop is basedthe6dBdrop is based

Toapplythetechniquethe beamisscannedovertheToapplythetechniquethe beamisscannedoverthe

discontinuityandnoteismadeoftheechoheightjustdiscontinuityandnoteismadeoftheechoheightjustpriortoitsrapidfall asthe beam passesovertheedgeofpriortoitsrapidfall asthe beam passesovertheedgeofthediscontinuitythediscontinuity


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6dB drop tip location technique6dB drop tip location technique

Onlyapplicable withrelativelyhighdegreeofaccuracyOnlyapplicable withrelativelyhighdegreeofaccuracytorelativelysmoothsurfaceddiscontinuities,torelativelysmoothsurfaceddiscontinuities,

perpendiculartothe beamaxis.perpendiculartothe beamaxis. Onlyapplicable wherethedimensionsto bemeasuredOnlyapplicable wherethedimensionsto bemeasured

areat leastequal tothe6dB beam widthattherangeofareat leastequal tothe6dB beam widthattherangeofthediscontinuitythediscontinuity

Thetechniqueis betterabletoaccommodatevariationsThetechniqueis betterabletoaccommodatevariationsinechoheightalongthedirectionto bemeasuredthaninechoheightalongthedirectionto bemeasuredthanthe6dBdrop frommaximum. However,itisnotthe6dBdrop frommaximum. However,itisnotalwayseasyfortheoperatortodecidetheechoheightalwayseasyfortheoperatortodecidetheechoheightlevel on whichthe6dBdrop should be basedlevel on whichthe6dBdrop should be based


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Beam axis tip location techniqueBeam axis tip location technique

Thetechniqueis basedonthe principlethan whenanThetechniqueis basedonthe principlethan whenan

individual peak, withintheoverall echofromaindividual peak, withintheoverall echofroma

discontinuity,isatmaximumamplitude,thefacetofthediscontinuity,isatmaximumamplitude,thefacetofthe

discontinuitygivingrisetothat peakwill lieonthediscontinuitygivingrisetothat peakwill lieonthebeamaxis.beamaxis.


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Beamaxis tiplocation techniqueBeamaxis tiplocation technique

1:Echo A atmaximumheight1:Echo A atmaximumheight

2: Variationon peaksignal amplitude2: Variationon peaksignal amplitude

3:Echo A1atmaximumheight3:Echo A1atmaximumheight

4: A scan4: A scan

5:Echo A will bethefirstappear5:Echo A will bethefirstappear

whenmoving probe backwardswhenmoving probe backwards6:Echo A will bethefirstappear6:Echo A will bethefirstappear

whenmoving probeforwardswhenmoving probeforwards


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Beam axis tip location technique

Capableofdeterminingtheactual discontinuityCapableofdeterminingtheactual discontinuitydimensionstoarelativelyhighdegreeofaccuracy;dimensionstoarelativelyhighdegreeofaccuracy;

OnlyapplicabletodiscontinuitieshavingdimensionsOnlyapplicabletodiscontinuitieshavingdimensionsabovetherangeresolutionofthe probe,andshowingabovetherangeresolutionofthe probe,andshowingtwoormoreamplitude peakseitheronthe Atwoormoreamplitude peakseitheronthe A--scanscan

presentationoralongtheechoenvelopepresentationoralongtheechoenvelope RequiresexperienceandjudgementinchoosingtheRequiresexperienceandjudgementinchoosingthe

mostsuitableangleofincidenceandinidentifyingthemostsuitableangleofincidenceandinidentifyingthecorrect peaksfromtheedgesofthediscontinuity.correct peaksfromtheedgesofthediscontinuity.


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1:1: Echo A at 20dB belowEcho A at 20dB below

maximumheightmaximumheight

2:2: Variationon peaksignalVariationon peaksignal

amplitudeamplitude

3:3: Echo A1at 20dB belowEcho A1at 20dB below

maximumheightmaximumheight4:4: A scanA scan

5:5: 20dBedge20dBedge


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20 dB drop tip location technique

Thetechniqueissimilartothe beamaxistip locationtechniqueThetechniqueissimilartothe beamaxistip locationtechniqueexceptthatthe 20dB beamedgeis usedto positiontheedgeofexceptthatthe 20dB beamedgeis usedto positiontheedgeof

thediscontinuity.thediscontinuity. Toapplythetechnique,theindividual peakfromthetip oftheToapplythetechnique,theindividual peakfromthetip ofthe

discontinuityorthe lastreflectingfacetadjacenttoitsedge,isdiscontinuityorthe lastreflectingfacetadjacenttoitsedge,isfirstidentified. This peakisthenmaximisedand probemovementfirstidentified. This peakisthenmaximisedand probemovement

continuedawayfromtheedge until itsechoheighthasfallen bycontinuedawayfromtheedge until itsechoheighthasfallen by20dB below itsmaximumvalue. The positionoftheedgeisthen20dB below itsmaximumvalue. The positionoftheedgeisthenplottedoutalongthe 20dBedgeofthe beamthathas beenplottedoutalongthe 20dBedgeofthe beamthathas beenpreviouslydetermined.previouslydetermined.


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20 dB drop tip location technique20 dB drop tip location technique

Capableofdeterminingtheactual discontinuitydimensionstoaCapableofdeterminingtheactual discontinuitydimensionstoarelativelyhighdegreeofaccuracyrelativelyhighdegreeofaccuracy

Applicabletoall discontinuitiesabovethe proberesolution,Applicabletoall discontinuitiesabovethe proberesolution,eitheronthe Aeitheronthe A--scope presentation,oralongtheechoenvelopescope presentation,oralongtheechoenvelope

The 20dB beamedgemust be plotted usingaseriesofsmallThe 20dB beamedgemust be plotted usingaseriesofsmallcircularreflectors,suchas1,5 mmsidecircularreflectors,suchas1,5 mmside--drilledholes;drilledholes;

Theneedtoaccurately plotthe beamedge beforetakinganyTheneedtoaccurately plotthe beamedge beforetakinganymeasurementisanadditional possiblesourceoferrorcomparedmeasurementisanadditional possiblesourceoferrorcomparedtothe beamaxistip locationtechnique;tothe beamaxistip locationtechnique;

RequiresexperienceandjudgementinchoosingthemostsuitableRequiresexperienceandjudgementinchoosingthemostsuitableangleofincidenceandinidentifyingtheindividual peaksfromangleofincidenceandinidentifyingtheindividual peaksfrom

theedgesofthediscontinuity.theedgesofthediscontinuity.


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CHN PHNG PHP NHGI LN KHUYT TT

maximumechoheighttechniques (DGS, DAC)formeasureddimension lessthanthe6dB beam width

fixedamplitude level techniques (DAC-6dB,-12dB)for

discontinuitiesspecificallycalledforintheacceptancestandard techniques basedon probemovementataspecifieddBdrop (6,

12, 20dB) below themaximumechoheightfordiscontinuitiesgreaterthanthe beam widthatthesamedBdrop.

techniques basedon positioningtheindividual edgesofadiscontinuityforthediscontinuityshowstwoormoreresolvableechomaxima;

thehighestreliabilityandaccuracytechniqueshall beassumedtobecorrect.

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