ASTM E797 Pulso Eco

8/8/2019 ASTM E797 Pulso Eco

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Standard Practice for Measuring Thickness by Manual Ultrasonic Pulse-EchoContact Method

This standard is issued under the fixed designation E 797; the nuber iediately follo!ing thedesignation indicates the year of

original ado"tion or# in the case of re$ision# the year of last re$ision% & nuber in "arenthesesindicates the year of last rea""ro$al% &su"erscri"t e"silon 'e( indicates an editorial change since the last re$ision or rea""ro$al%

)% Sco"e)%) This "ractice* "ro$ides guidelines for easuring thethickness of aterials using the contact "ulse-echo ethod atte"eratures not to exceed *++, '9.,C(%)%* This "ractice is a""licable to any aterial in !hichultrasonic !a$es !ill "ro"agate at a constant $elocity throughoutthe "art# and fro !hich back reflections can be obtainedand resol$ed%)%. The $alues stated in either inch-"ound or S/ units are to

be regarded as the standard% The $alues gi$en in "arenthesesare for inforation only%)%0 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appropriatesafety and health practices and determine the applicability of regulatory limitations prior to use.

*% 1eferenced 2ocuents*%) ASTM Standards:E .)7 Practice for E$aluating Perforance Characteristicsof Ultrasonic Pulse-Echo Testing Systes 3ithout the Useof Electronic Measureent /nstruents.E 090 Practice for Measuring Ultrasonic 4elocity in Materials.E ).)5 Terinology for 6ondestructi$e Exainations.*%* ASNT Document:Nondestructie Testing !andboo" # *nd Edition# 4ol 70.% Terinology.%) Definitionsor definitions of ters used in this"ractice# refer to Terinology E ).)5%0% Suary of Practice0%) Thickness 'T (# !hen easured by the "ulse-echo ultrasonicethod# is a "roduct of the $elocity of sound in the aterial and one half the transit tie 'roundtri"( through theaterial%T 8

#t *!hereT 8 thickness## 8 $elocity# andt 8 transit tie%0%* The "ulse-echo ultrasonic instruent easures the transittie of the ultrasonic "ulse through the "art%0%. The $elocity in the aterial under test is a function of the "hysical "ro"erties of the aterial% /t is usually assued tobe a constant for a gi$en class of aterials% /ts a""roxiate$alue can be obtained fro Table :.%) in Practice E 090 or fro the Nondestructie Testing !andboo" # or it can be

deterined e"irically%0%0 ne or ore reference blocks are re<uired ha$ingkno!n $elocity# or of the sae aterial to be tested# and



ha$ing thicknesses accurately easured and in the range of thicknesses to be easured% /t is generally desirable that thethicknesses be =round nubers> rather than iscellaneous odd$alues% ne block should ha$e a thickness $alue near theaxiu of the range of interest and another block near theiniu thickness%

0%8 The dis"lay eleent 'C1T 'cathode ray tube(# eter# or digital dis"lay( of the instruent ust be ad?usted to "resentcon$enient $alues of thickness de"endent on the range beingused% The control for this function ay ha$e different naes ondifferent instruents# including range, sweep, material calibrate#or elocity %0%5 The tiing circuits in different instruents use $ariouscon$ersion schees% & coon ethod is the so-calledtie@analog con$ersion in !hich the tie easured by theinstruent is con$erted into a "ro"ortional dc $oltage !hich isthen a""lied to the readout de$ice% &nother techni<ue uses a$ery high-fre<uency oscillator that is odulated or gated by the

a""ro"riate echo indications# the out"ut being used either directly to suitable digital readouts or con$erted to a $oltage for other "resentation% & relationshi" of transit tie $ersus thicknessis sho!n gra"hically in ig% )%

8% Significance and Use8%) The techni<ues described "ro$ide indirect easureent

of thickness of sections of aterials not exceeding te"eraturesof *++, '9.,C(% Measureents are ade fro one sideof the ob?ect# !ithout re<uiring access to the rear surface%8%* Ultrasonic thickness easureents are used extensi$elyon basic sha"es and "roducts of any aterials# on "recisionachined "arts# and to deterine !all thinning in "rocess

e<ui"ent caused by corrosion and erosion%8%. 1ecoendations for deterining the ca"abilities andliitations of ultrasonic thickness gages for s"ecific a""licationscan be found in the cited references%

5% &""aratus5%) InstrumentsThickness-easureent instruents aredi$ided into three grou"s '$( la! detectors !ith C1T readout#'% ( la! detectors !ith C1T and direct thickness readout# and'&( 2irect thickness readout%5%)%) la! detectors !ith C1T readouts dis"lay tie@a"litude inforation in an &-scan "resentation% Thicknessdeterinations are ade by reading the distance bet!een the

Aero-corrected initial "ulse and first-returned echo 'back reflection(#or bet!een ulti"le-back reflection echoes# on a calibratedbase line of a C1T% The base line of the C1T should bead?usted for the desired thickness increents%

5%)%* la! detectors !ith nueric readout are a cobination"ulse ultrasound fla! detection instruent !ith a C1T andadditional circuitry that "ro$ides digital thickness inforation%The aterial thickness can be electronically easured and"resented on a digital readout% The C1T "ro$ides a check onthe $alidity of the electronic easureent by re$ealing easureent$ariables# such as internal discontinuities# or echostrength$ariations# !hich ight result in inaccurate readings%

5%)%. Thickness readout instruents are odified $ersionsof the "ulse-echo instruent% The ela"sed tie bet!een theinitial "ulse and the first echo or bet!een ulti"le echoes is



con$erted into a eter or digital readout% The instruents aredesigned for easureent and direct nuerical readout of s"ecific ranges of thickness and aterials%5%* Search 'nitsMost "ulse-echo ty"e search units'straight-bea contact# delay line# and dual eleent( area""licable if fla! detector instruents are used% /f a thickness

readout instruent has the ca"ability to read thin sections# ahighly da"ed# high-fre<uency search unit is generally used%Bigh-fre<uency ')+ MBA or higher( delay line search units aregenerally re<uired for thicknesses less than about +%5 '+%+*8 in%(% Measureents of aterials at high te"eraturesre<uire search units s"ecially designed for the a""lication%3hen dual eleent search units are used# their inherentnonlinearity usually re<uires s"ecial corrections for thin sections%'See ig% *%( or o"tiu "erforance# it is oftennecessary that the instruent and search units be atched%5%. (alibration )loc"sThe general re<uireents for a""ro"riatecalibration blocks are gi$en in 0%0# 7%)%.# 7%*%*%)#

7%.%*# and 7%0%.% Multi-ste" blocks that ay be useful for thesecalibration "rocedures are described in &""endix :) 'igs%:)%) and :)%*(%

7% ProcedureCalibration and &d?ustent of &""aratus7%) (ase I*Direct (ontact, Single+lement Search 'nit 7%)%) (onditionsThe dis"lay start is synchroniAed to theinitial "ulse% &ll dis"lay eleents are linear% ull thickness isdis"layed on C1T%7%)%* Under these conditions# !e can assue that the$elocity con$ersion line effecti$ely "i$ots about the origin'ig% )(% /t ay be necessary to subtract the !ear-"late tie#re<uiring inor use of delay control% /t is recoended thattest blocks "ro$iding a iniu of t!o thicknesses that s"anthe thickness range be used to check the full-range accuracy%

7%)%. Place the search unit on a test block of kno!nthickness !ith suitable cou"lant and ad?ust the instruentcontrols 'aterial calibrate# range# s!ee"# or $elocity( until thedis"lay "resents the a""ro"riate thickness reading%7%)%0 The readings should then be checked and ad?usted ontest blocks !ith thickness of lesser $alue to i"ro$e the o$erallaccuracy of the syste%7%* (ase II*Delay -ine Single+lement Search 'nit 7%*%) (onditions3hen using this search unit# it is necessarythat the e<ui"ent be ca"able of correcting for the tieduring !hich the sound "asses through the delay line so that

the end of the delay can be ade to coincide !ith Aerothickness% This re<uires a so-called =delay> control in theinstruent or autoatic electronic sensing of Aero thickness%

7%*%* /n ost instruents# if the aterial calibrate circuit!as "re$iously ad?usted for a gi$en aterial $elocity# the delaycontrol should be ad?usted until a correct thickness reading isobtained on the instruent% Bo!e$er# if the instruent ust beco"letely calibrated !ith the delay line search unit# thefollo!ing techni<ue is recoended7%*%*%) Use at least t!o test blocks% ne should ha$e athickness near the axiu of the range to be easured andthe other block near the iniu thickness% or con$enience#

it is desirable that the thickness should be =round nubers> sothat the difference bet!een the also has a con$enient =round



nuber> $alue%7%*%*%* Place the search unit se<uentially on one and thenthe other block# and obtain both readings% The differencebet!een these t!o readings should be calculated% /f the readingthickness difference is less than the actual thickness difference#"lace the search unit on the thicker s"ecien# and ad?ust the

aterial calibrate control to ex"and the thickness range% /f thereading thickness difference is greater than the actual thicknessdifference# "lace the search unit on the thicker s"ecien# andad?ust the aterial calibrate control to decrease the thicknessrange% & certain aount of o$er correction is usually recoended%1e"osition the search unit se<uentially on bothblocks# and note the reading differences !hile aking additionala""ro"riate corrections% 3hen the reading thicknessdifferential e<uals the actual thickness differential# the aterialthickness range is correctly ad?usted%&single ad?ustent of thedelay control should then "erit correct readings at both thehigh and lo! end of the thickness range%7%*%. &n alternati$e techni<ue for delay line search units is

a $ariation of that described in 7%*%*% & series of se<uentialad?ustents are ade# using the =delay> control to "ro$idecorrect readings on the thinner test block and the =range>control to correct the readings on the thicker block% Moderateo$er-correction is soeties useful% 3hen both readings are=correct> the instruent is ad?usted "ro"erly%7%. (ase III*Dual Search 'nits7%.%) The ethod described in 7%* 'Case //( is also suitablefor e<ui"ent using dual search units in the thicker ranges#abo$e . '+%)*8 in%(% Bo!e$er# belo! those $alues there isan inherent error due to the 4ee "ath that the sound beatra$els% The transit tie is no longer linearly "ro"ortional tothickness# and the condition deteriorates to!ard the lo!

thickness end of the range% The $ariation is also sho!nscheatically in ig% *'a(% Ty"ical error $alues are sho!n inig% *'b(%7%.%* /f easureents are to be ade o$er a $ery liitedrange near the thin end of the scale# it is "ossible to calibratethe instruent !ith the techni<ue in Case // using a""ro"riatethin test blocks% This !ill "roduce a correction cur$e that isa""roxiately correct o$er that liited range% 6ote that it !illbe substantially in error at thicker easureents%7%.%. /f a !ide range of thicknesses is to be easured# itay be ore suitable to calibrate as in Case // using test blocksat the high end of the range and "erha"s half!ay to!ard thelo! end% ollo!ing this# e"irical corrections can be established

for the $ery thin end of the range%7%.%0 or a direct-reading "anel-ty"e eter dis"lay# it is

con$enient to build these corrections into the dis"lay as anonlinear function%7%0 (ase I#*Thic" Sections7%0%) (onditionsor use !hen a high degree of accuracyis re<uired for thick sections%7%0%* 2irect contact search unit and initial "ulse synchroniAationare used% The dis"lay start is delayed as described in7%0%0% &ll dis"lay eleents should be linear% /ncreentalthickness is dis"layed on the C1T%7%0%. asic calibration of the s!ee" !ill be ade as

described in Case /% The test block chosen for this calibrationshould ha$e a thickness that !ill "erit calibrating thefull-s!ee" distance to ade<uate accuracy# that is# about )+



'+%0 in%( or *8 ')%+ in%( full scale%7%0%0 &fter basic calibration# the s!ee" ust be delayed%or instance# if the noinal "art thickness is ex"ected to befro 8+ to 5+ '*%+ to *%0 in%(# and the basic calibrationblock is )+ '+%0 in%(# and the increental thicknessdis"layed !ill also be fro 8+ to 5+ '*%+ to *%0 in%(# the

follo!ing ste"s are re<uired% &d?ust the delay control so thatthe fifth back echo of the basic calibration block# e<ui$alent to8+ '*%+ in%(# is aligned !ith the + reference on the C1T%The sixth back echo should then occur at the right edge of thecalibrated s!ee"%7%0%8 This calibration can be checked on a kno!n block of the a""roxiate total thickness%7%0%5 The reading obtained on the unkno!n s"ecien ustbe added to the $alue delayed off screen% or exa"le# if thereading is 0 '+%)5 in%(# the total thickness !ill be 80 '*%)5 in%(%D% Technical BaAardsD%) 2ual search units ay also be used effecti$ely !ith

rough surface conditions% /n this case# only the first returnedecho# such as fro the botto of a "it# is used in theeasureent% enerally# a localiAed scanning search is adeto detect the iniu reaining !all%D%* Material ropertiesThe instruent should be calibratedon a aterial ha$ing the sae acoustic $elocity andattenuation as the aterial to be easured% 3here "ossible#calibration should be confired by direct diensional easureentof the aterial to be exained%D%. Scanning The axiu s"eed of scanning should bestated in the "rocedure% Material conditions# ty"e of e<ui"ent#and o"erator ca"abilities ay re<uire slo!er scanning%D%0 /eometry

D%0%) Bighest accuracy can be obtained fro aterials !ith"arallel or concentric surfaces% /n any cases# it is "ossible toobtain easureents fro aterials !ith non"arallel surfaces%Bo!e$er# the accuracy of the reading ay be liited and thereading obtained is generally that of the thinnest "ortion of thesection being interrogated by the sound bea at a gi$en instant%D%0%* 1elati$ely sall diaeter cur$es often re<uire s"ecialtechni<ues and e<ui"ent% 3hen sall diaeters are to beeasured# s"ecial "rocedures including additional s"eciensay be re<uired to ensure accuracy of setu" and readout%D%8 Bigh-te"erature aterials# u" to about 80+,C')+++,(# can be easured !ith s"ecially designed instruents!ith high te"erature co"ensation# search unit asseblies#

and cou"lants% 6oraliAation of a""arent thickness readingsfor ele$ated te"eratures is re<uired% & rule of thub oftenused is as follo!s The a""arent thickness reading obtainedfro steel !alls ha$ing ele$ated te"eratures is high 'toothick( by a factor of about ) F "er 88,C ')++,(% Thus# if theinstruent !as calibrated on a "iece of siilar aterial at *+,C'5D,(# and if the reading !as obtained !ith a surfacete"erature of 05+,C 'D5+,(# the a""arent reading should bereduced by D F% This correction is an a$erage one for anyty"es of steel% ther corrections !ould ha$e to be deterinede"irically for other aterials%

D%5 Instrument Tie base linearity is re<uired so that achange in the thickness of aterial !ill "roduce a corres"ondingchange of indicated thickness% /f a C1T is used as a



readout# its horiAontal linearity can be checked by usingPractice E .)7%D%7 )ac" 0eflection 1aetrain2irect-thickness readoutinstruents read the thickness at the first half cycle of the!a$etrain that exceeds a set a"litude and a fixed tie% /f thea"litude of the back reflection fro the easured aterial is

different fro the a"litude of the back reflection fro thecalibration blocks# the thickness readout ay read to a differenthalf cycle in the !a$etrain# thereby "roducing an error% Thisay be reduced byD%7%) Using calibration blocks ha$ing attenuation characteristicse<ual to those in the easured aterial or ad?usting backreflection a"litude to be e<ual for both the calibrating blocksand easured aterial%D%7%* Using an instruent !ith autoatic gain control to"roduce a constant a"litude back reflection%D%D 0eadoutsC1T dis"lays are recoended !here reflectingsurfaces are rough# "itted# or corroded%D%D%) 2irect-thickness readout# !ithout C1T# "resents haAards

of isad?ustent and isreading under certain testconditions# es"ecially thin sections# rough corroded surfaces#and ra"idly changing thickness ranges%D%9 (alibration Standardsreater accuracy can be obtained!hen the e<ui"ent is calibrated on areas of kno!nthickness of the aterial to be easured%D%)+ 4ariations in echo signal strength ay "roduce an error e<ui$alent to one or ore half-cycles of the 1 fre<uency#de"endent on instruentation characteristics%

9% Procedure 1e<uireents9%) /n de$elo"ing the detailed "rocedure# the follo!ingites should be considered

9%)%) /nstruent anufacturerGs o"erating instructions%9%)%* Sco"e of aterials@ob?ects to be easured%9%)%. &""licability# accuracy re<uireents%9%)%0 2efinitions%9%)%8 1e<uireents%9%)%8%) Personnel%9%)%8%* E<ui"ent%9%)%8%. Procedure <ualification%9%)%5 Procedure%9%)%5%) Measureent conditions%9%)%5%* Surface "re"aration and cou"lant%9%)%5%. Calibration and allo!able tolerances%9%)%5%0 Scanning "araeters%

9%)%7 1e"ort%9%)%7%) Procedure used%9%)%7%* Calibration record%9%)%7%. Measureent record%)+% 1e"ort)+%) 1ecord the follo!ing inforation at the tie of theeasureents and include it in the re"ort)+%)%) /ns"ection "rocedure%)+%)%)%) Ty"e of instruent%)+%)%)%* Calibration blocks# siAe and aterial ty"e%)+%)%)%. SiAe# fre<uency# and ty"e of search unit%)+%)%)%0 Scanning ethod%)+%)%* 1esults%

)+%)%*%) Maxiu and iniu thickness easureents%)+%)%*%* Hocation of easureents%)+%)%. Personnel data# certification le$el%



))% Iey!ords))%) contact testing; nondestructi$e testing; "ulse-echo;thickness easureent; ultrasonics

ASTM E797 Pulso Eco

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