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TOFD-101 Time of Flight Diraction Diraction Level II Training Cost: $ 1,595.00 per student Cost: $ Duration: 40 Hours Duration: 40 Prerequisites: UT Level II certifcation or minimum o 0 !ours conventional UT trainin". Prerequisites: UT qui!ment "ee#e#: #ll "ee#e#: #ll euipment, includin" scope, is provided or t!is class. #ttendees are encoura"ed to %rin" t!eir o&n personnel scope i t!e' !ave one %ut it is not reuired. For an O"$IT %&OT or %&OT or to '(I$T' '(I$T' contact contact us at: info)universit*ofultrasonics+com
Course Descri!tion
T!is course covers covers t!e %asic %asic t!eor' and and euipment euipment operation associated associated &it! &it! t!e time o (i"!t di)raction *T+- tec!niue. +ur trainin" classes %lend t!eoretical trainin" and la% e/ercises to !elp ma/imie t!e learnin" potential. e prepare 'ou %' trainin" &it! state o t!e art euipment and !ave one t!e lar"est collections o real (a&ed samples &!ic! also !elp prepare individuals or t!e real &orld.
T!is 40 Hour &ill fll t!e ormal trainin" reuire reuirements ments i see2in" see2in" certifcation certifcation in T+- to 3T 3T T61# T61 # or 6719. 6719. T!is class ollo&s ollo&s and ulflls ulflls t!e Topical +utline or or 8ualifcation o ondestructive Testin" 7ersonnel 67105.
us at an' time. I 'ou !ave an' additional uestions please eel ree to contact us at ,vailale Classes: Training Calen#ar
TOFD Course Outline ave p!'sics and properties o Ultrasonic T+-
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T+- 7ro%es 7ro%es and ed"es ed"es
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eatures and desi"n
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eam 6!aracteristic 6!aracteristics s
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7roper euipment selection Instrument control and 6ali%ration
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asic instrument parameters
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ed"e -ela' and :elocit' cali%rations
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763 6ali%rations 3can plannin", development, and practice
Handson T+- 6ali%ration and ?/amination La%orator' e/ercises.
&niversit* of <rasonics 6op'ri"!t @ ;015 #ll Ai"!ts Aeserved
Structural integrity with Time of Flight Diffraction (TOFD) ultrasonic inspection Bryan Kenzie and Julian Speck
Bryan Kenzie is a principal NDT engineer at who undertaes a range of inspection de!elopment pro"ects and leads T#$%s participation in the TOFD&'OOF pro"ect ulian Spec is T#$%s structural integrity department manager* responsi+le for FFS and 'B$ pro"ects and de!elopment acti!ities &aper pu+lished in $nspectioneering ournal uly,-ugust .//0
TOFD inspection technology This article is intended to pro!ide a summary of the issues surrounding the use of the ultrasonic Time of Flight Diffraction (TOFD) techni1ue TOFD was de!eloped for the 2K nuclear industry during the 345/s to pro!ide a method formeasuring the height of planar flaws TOFD is now generally recognised as the most accurate ultrasonic techni1ue for measuring the height of em+edded planar flaws (eg cracs* lac of fusion* etc) that lie perpendicular to !essel orpipe surfaces 6ommercial TOFD systems (eg 7$6'O&82S) ha!e +een a!aila+le for some time from a range of suppliers (-n independent +uyers% guide can +e found on the we+site of the British $nstitute of Non9Destructi!e Testing atwww+indtorg) -t present* national standards for the application of TOFD e:ist ;owe!er* no standardised acceptance criteria ha!e +een agreed upon for pre9ser!ice (fa+rication) inspectionTherefore* for pre9ser!ice inspection* TOFD is commonly used with flaw acceptance criteria deri!ed +y engineering critical assessments (<6-) as descri+ed in BS543/
;ow does TOFD wor= 7ost ultrasonic techni1ues rely on recei!ing reflections from flaws* e!en if only from particular facets of the flaws TOFD detects cracs using the signals diffracted from the flaw%s e:tremities (tips) Two angled compression wa!epro+es (typically +etween . to 3/7;z fre1uency) are used in transmit9recei!e mode* one pro+e each side of the weld The +eam di!ergence is such that the ma"ority of the thicness is inspected* although* for thicer components* morethan one pro+e separation may +e re1uired #hen the sound stries the tip of a crac* this acts as a secondary emitter that scatters sound out in all directions (some in the direction of the recei!ing pro+e)* Fig.1
Fig 3 Basic TOFD two9pro+e configuration
- %lateral wa!e% tra!elling at the same !elocity as the compression wa!es* tra!els directly from the transmitter to the recei!er The time difference +etween the lateral wa!e and the diffracted signal from the flaw pro!ides a measure of its distance from the scanned surface $f the flaw is large enough in the through9wall (height) dimension* it may +e possi+le to resol!e the tip diffracted signals from its top and +ottom* there+y allowing the through wall height of the flaw to +e measured
TOFD signal interpretation Due to the low amplitude of the diffracted signals* TOFD is usually carried out using a preamplifier and hardware designed to impro!e signal9to9noise performance -s the pro+es are scanned along the weld* the -9Scan signals aredigitised* Fig.2
Fig . Typical -9scan showing responses from an e m+edded planar flaw
The signals are displayed as a grey9scale image with flaws as alternating white and +lac fringes* Fig.3 The diffracted signals from the e:tremities appear as signals arri!ing at different times at the recei!er By carrying out geometric calculations an estimation of the through thicness dimension of a flaw can +e o+tained
Fig > &ro+e mo!ement and image orientation
This results in a series of images of a weld showing the flaw positions in B9scan !iew (from end of weld* or cross section)* 69scan !iew (looing through weld from cap side* or plan !iew)* and D9scan !iew (from side* showing weld length and height) TOFD can also utilise synthetic aperture focusing and,or +eam modelling software to minimise the effects of +eam di!ergence This can pro!ide more accurate location and sizing information
$n9ser!ice inspection with TOFD TOFD is a !ery rapid method of inspecting whole !olumes $t is most widely used in the nuclear and oil refining and petrochemical industries* for the in9ser!ice inspection of +utt welds in pressure !essels* process pipewor* etcThe results are then commonly used in fitness for ser!ice (FFS) assessments* in accordance with* eg -&$ '&054 (For an FFS assessment of a nown flaw* information a+out flaw length and height for em+edded and surface flaws* is re1uired $t is also important to determine the component thicness and the flaw orientation with respect to the principal stress direction* and whether or not the flaw cross9section is planar) $n the past* colla+orati!e 2T trials carried out at T#$ and elsewhere in the 2K found that typical errors on planar flaw height measurement* using the ./dB9drop techni1ue +y operators on %the shop floor% and in %the la+oratory%*ranged from a mean error of 93/mm (undersize) with a standard de!iation of >3mm* to a mean error of 9.5mm with a standard de!iation of >/mm* Fig.4
Fig ? The standard ./dB9drop 2T techni1ue generally undersizes* compared to TOFD
The TOFD sizing techni1ue pro!ides a +etter correlation +etween measured and actual flaw heights than the ./dB9drop techni1ue* Fig.4 The colla+orati!e trials also found that typical errors on planar flaw height measurement using TOFD had a mean of @/0mm (o!ersize) with a standard de!iation of 3Amm The actual flaw heights in!estigated in the studyranged from 30 to >/mm
Some important shortcomings of TOFD FFS engineers should +e aware that the techni1ue +ecomes less relia+le when
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The material contains scattered inclusions (eg inclusions in %!intage% steels)C There is a high density of defects due to* eg hydrogen damageC and $nspecting coarser grained materials (austenitic stainless steel weldments)
The detection of small flaws near the scan surface* can +e more difficult due to the presence of the lateral wa!e response which often occupies se!eral millimetres of the depth a:is on images TOFD is restricted where signal timedifferences are small so that the different signals cannot +e resol!ed in time* eg for small flaws close to the +acwall (far surface) The roots of a single9!ee pipe +utt weld ha!e specific difficulties for 2T inspection in general* due to the fact that the root geometry itself can +e a source of ultrasonic signals -nother difficulty occurs when there is high9lowin +utt welded "oints (due to thicness !ariation and,or misalignment) This can mean small flaws are hidden +y corner echoes and there is a potential for false calls
- special case $n9ser!ice wet ; .S damage 6ar+ons steels in wet ;.S ser!ice may +e suscepti+le to a range of damage mechanisms that gi!e rise to surface and em+edded cracs* ie sulphide stress corrosion cracing (SS66) and stress oriented hydrogen induced cracing (SO;$6)-&$ '&053 pro!ides a comprehensi!e discussion on these wet ; . S damage mechanisms* including methods for monitoring and inspection '&053 suggests ultrasonic testing for the detection and sizing of cracs in wet ; . S ser!ice The TOFD techni1ue is often considered for this application +ut it has some limitationsC the ad!antage of using TOFD for initial flaw detection is not so certain For e:ample* it is +est suited for the detection of flaws that do notlie close to* or +rea* a surface which can +e important when trying to detect internal surface cracs during e:ternal (non9intrusi!e) TOFD inspection $t is therefore recommended that pulse9echo shear wa!e 2T is used for initialdetection scans* unless a TOFD procedure has +een !alidated for the detection of all ; . S flaw types and sizes of interest TOFD should then +e used to specifically target any such flaws in an attempt to determine their size Due to image interpretation difficulties* it should also +e e:pected that TOFD scans may +e incapa+le of relia+ly sizing SO;$6 (particularly em+edded cracs* during the earliest stages of crac de!elopment)* Fig.5 SO;$6 is commonly o+ser!ed in weldments in the +ase metal ad"acent to the heat affected zone (;-)* oriented in the through9thicness direction SO;$6 descri+es an array of cracs* aligned perpendicular to the weldingresidual stress* that are formed +y the lin9up of small hydrogen induced cracs in steel The worst SO;$6 case would +e through9wall connected (stepwise) cracs* perpendicular to one of the principal mem+rane stresses from* egpressure loading
Fig 0 Schematic of SO;$6 damage at a weld* that may or not +e connected
TOFD relies hea!ily on the correct interpretation of data images* which can sometimes +e difficult $n the case of in9ser!ice inspection for the detection of SO;$6* the indications from numerous harmless steel inclusions (typical ofa poor 1uality steels suscepti+le to wet ; . S damage) can mae the identification of more serious flaws (connected SO;$6 cracs) e:tremely difficult $nspection engineers should +e aware that this may lead to conser!ati!e false calls and unnecessaryrepairsE
