UUltrasonic technicians have variedexperience and analytical skills. Themore exposure to different signalcharacteristics, techniques andindication images, the better theiranalysis skills will be. During theperiod when the technician isaccumulating the experience andskills, there must be an oversightprocess for the thorough andproper evaluation of indicationsand to minimize false calls.In the chemical industry,

ammonia pressure vessels have ahistory of extensive weld cracks.Detection and evaluation isconducted by using advancedultrasonic techniques such as timeof flight diffraction (ToFD),phased array ultrasonics and hightemperature angle beam

ultrasonics. The time of flightdiffraction technique is moreeffectively used for hightemperature scanning.

Initial Inspections Using PhasedArray Ultrasonic Testing

The following case involved apressure vessel within a cluster ofammonia plants. An initialinspection was conducted atambient temperature during a plantshutdown. Phased array ultrasonictesting was conducted on a total ofsix meridian welds (sometimesdescribed as orange peel welds) ofa vessel’s bottom head (Fig. 1).The technician reported cracks

on all six of the welds. Based uponthe findings, the client evaluatedfitness for service and determinedthat it was safe to operate thevessel with the reported cracks.Periodic monitoring was requiredas a condition of continuedoperation.

Periodic Monitoring UtilizingTime of Flight Diffraction

The periodic monitoring wasconducted while the plant wasoperating by an inspection crewspecializing in onstream or onlineinspection. The online examinationwas conducted at 291 °C (556 °F),

theNDT Technician

The American Society for Nondestructive Testingwww.asnt.org

FOCUS

A Cautionary Tale by Ronald T. Nisbet*

FOCUS continued on page 2.

TNT · July 2013 · 1Vol. 12, No. 3

*QUALSPEC; IESCO LLC –International Energy ServicesCompany; 3445 Kashiwa St.,Torrance, CA 90505; (310) 257-8222,fax (310) 257-8220;rnisbet@qualspecgroup.com.

Figure 1. Display for phased arraytests of pressure vessel meridianwelds shows attachment indicationinterpreted as crack.

using time of flight diffraction. This time however, nocracks were reported (Fig. 2). The inspection company’sLevel III analyst reviewed the test data and confirmed thatthere was no evidence of cracking. Additional testing wasconducted using conventional ultrasonic shear wave anglebeam examination. Again no cracks were reported. Understandably, the client was concerned. Why were

time of flight diffraction and the conventional ultrasonicshear wave angle beam that followed unable to find thecracks originally reported by phased array ultrasonics? Didthe high temperature affect the inspection? The Level IIIanalyst requested the original ultrasonic phased arrayinspection data, but none had been retained. The originalreport however, was available and showed each crack to beof the same length and in the same location on each ofthe six welds. The Level III analyst then suggested theclient review the construction drawings for the vessel. Itwas discovered these locations corresponded to internalattachment welds on the original drawings.These indications at the attachment welds appeared later

in time (at a greater distance) than that of the vessel headinternal surface. The findings were demonstrated to theclient. It had become clear that the reported cracks werein fact signals from the attachment welds.

Solution

Advanced ultrasonic methods such as phased arrayultrasonics and time of flight diffraction, require extensivetraining and experience. Time of flight diffraction uses adifferent approach from conventional ultrasonic testing.One transducer transmits the ultrasonic energy whichinsonifies the area of interest. The other transducer

2 · Vol. 12, No. 3

FOCUS continued from page 1.

Tech Toon

IIn “A Cautionary Tale,” Ron Nisbet makes the point thatwhen the same condition, at the same point, over the samelength, on multiple welds, is observed, indications may be theresult of part geometry and not cracks. Uniformity in test

results can be a tell tale and some followup work should be in order.“Ultrasonic Examination of

Weldments — Characterizing Reflectors”is the second in a series of “FYI” articleson ultrasonic testing. The series isdesigned to improve results onperformance demonstration tests.The “Inbox” has another query on

ultrasonic testing and an in-depth response from the ASNTSenior Manager of Technical Services, James Houf. There’salso some helpful info for military vets regarding GI BillReimbursement for ASNT examinations.

Hollis Humphries, TNT EditorPO Box 28518, Columbus, Ohio 43228; (800) 222-2768X206; fax (614) 274-6899; e-mail hhumphries@asnt.org

FROM THE EDITOR

Figure 2. Scan for time of flight diffraction ultrasonic testsconducted during periodic online monitoring showing noindications in area previously interpreted as crack.

Distance, m (in.)

Time, µs

0.94 0.97 0.99 1.02 1.04 1.07 1.09 1.12 1.14 1.17 1.19 1.22(37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48)

50

55

60

65

70

75

80

Lateral wave(outside diameter)

Backwall (inside diameter)

functions as a receiver, collecting thesound wave and the instrumentationrecords images from anytip-diffracted signals. Interpretationrequires experience and access toimages of many signals fromdifferent types of discontinuities.Phased array ultrasonics can scanthrough a range of angleselectronically, which is the equivalentof making multiple angle beam shearwave scans at different angles.Prior to making a statement about

a significant crack which could causeshutdown of a plant and havesignificant financial ramifications, atechnician should call upon a reviewby a more experienced technician oranalyst. In many companies, theLevel III supervisor reviews all timeof-flight diffraction, phased arrayultrasonic testing and advanced dataprior to issuing a conclusion.

Moral of the Story

Don’t make a critical call withoutback up analysis, either by expertreview or by confirmation of resultsusing other methodologies. If originaldesign drawings or vessel fabricationrecords are available, they can be avaluable resource to confirm partgeometries or other fabrication issuesthat may not be readily apparent. Ifimages occur at regular intervals,geometry or internal attachments maybe the source of the signal. Crackimages typically have specificcharacteristics, due to their irregularshape, as well as variable lengths anddepths. Above all, advancedultrasonic processes have recordableimages that can easily be retaineddigitally and transmitted by e-mail toan experienced analyst forconfirmation.

TNT · July 2013 · 3

angle beam: Ultrasound beamtraveling at an acute angle into amedium. The angle of incidenceor angle of refraction is measuredfrom the normal to the entrysurface.

back reflection: Signal receivedfrom the far boundary or backsurface of a test object.

diffraction: Deflection of awavefront when passing the edgeof an ultrasonically opaque object.

insonification: Irradiation withsound.

phased array: Mosaic of transducerelements in which the timing ofthe elements’ excitation can beindividually controlled to producecertain desired effects, such assteering or focusing the beam.

reflection: General term for theprocess by which the incidentenergy leaves a surface or mediumfrom the incident side, withoutchange in frequency. Reflection isusually a combination of specularand diffuse reflection.

time of flight: Time for an acousticwave to travel between two points.For example, the time required fora pulse to travel from thetransmitter to the receiver viadiffraction at a discontinuity edgeor along the surface of the testobject.

transverse wave: Type of wave inwhich the particle motion isperpendicular to the direction ofpropagation. Also called shearwave.

ultrasonic: Of or relating toacoustic vibration frequenciesgreater than about 20 kHz.

ultrasonic testing: Method ofnondestructive testing, usingacoustic waves at inaudibly highfrequencies at the interrogatingenergy.

UT: Abbreviation for the ultrasonicmethod of nondestructive testing.

Glossary entries adapted from theNondestructive Testing Handbook.

Ultrasonic Testing

NDT GLOSSARY

TThis is the second in a series of three articles addressingultrasonic weld inspection as it pertains to the oil and gasindustries. The goal of the series is to improve results inperformance demonstration tests such as the AmericanPetroleum Institute (API) Qualification of UltrasonicExaminers Certification Program (QUTE) test and othersrequired by leading oil companies.

Identifying the Source of an Indication

What is the source of an indication? Does the reflectorresult from weld geometry or an actual discontinuity? Onceit has been determined that an indication is from adiscontinuity, it must be characterized. This process consistsof determining the location of the discontinuity by plottingthe beam sound path on a cross section of the weld andthen observing its signal characteristics.

Plotting Discontinuities

Ninety percent of the battle in discontinuity identification isin knowing where the discontinuity is located. Accurateplots are critical in determining the cross sectional positionof a discontinuity. When calibrating an angle beam probe, itis essential to measure the exit point and actual refractedangle since they will both change as the wedge wears.Indications must always be plotted. Relying solely on thesurface distance and depth information from thediscontinuity detector can often result in misidentifying adiscontinuity or mistaking geometry for a discontinuity.Before plotting, a cross section of the weld must be

drawn. A contour gage should be used to record the profileof the weld cap (Fig. 1). The geometries of test plates used

in most performance demonstration tests are typically veryconsistent, so obtaining a single profile from the weld capon any given weld is usually sufficient for plotting allindications. The geometry of field welds however, can bewildly erratic and it is therefore very important to obtain aprofile from each indication location when doing fieldinspections. Using a contour gage will make any mismatchor misalignment plainly evident once the bottom surface isdrawn in.After obtaining a profile of the weld cap, thickness

measurements must be obtained on the weld cap and onboth sides of the weld. The opposite surface of the partcan now be drawn. For single-V welds, a gap of 2.54 mm(0.1 in.) should be left on the far surface. This area is knownas the weld root.It is recommended that fusion lines not be drawn in when

examining test plates. Top surface weld toes on test platesoften overlap the bevel. Assuming that the bevel is at thetoe can lead to incorrectly identifying lack of sidewall fusionas slag.

An Old Subject Revisited: Ultrasonic Examination ofWeldments — Characterizing Reflectorsby Jeffrey L. Garner* and Ronald T. Nisbet*

FYI

4 · Vol. 12, No. 3

*QUALSPEC; IESCO LLC – International Energy ServicesCompany; 3445 Kashiwa St., Torrance, CA 90505;(310) 257-8222, fax (310) 257-8220; jgarner@qualspecgroup.com,rnisbet@qualspecgroup.com. Figure 1. Contour gage used to obtain weld profile.

If a discontinuity is plotted in the root area or in thefusion line, it is likely to be a planar discontinuity such as acrack, lack of fusion, or lack of penetration. If thediscontinuity is plotted in the body of the weld, it is likely tobe a volumetric discontinuity such as slag or porosity, with acenterline crack being the exception. Many performancedemonstration tests only require you to be able to tell thedifference between planar and volumetric discontinuities.Additional guidelines include the following.• Whenever possible, plot indications from both sides ofthe weld.

• Plot in both the first and second legs.• Use different angles since the response of an indicationto different angles can indicate the orientation of adiscontinuity.

Discontinuity Signal Characteristics

Practice is the best way to learn signal characteristics. Kitsare commercially available with small plates containing welddiscontinuities. Each plate has a different type of welddiscontinuity accompanied by a cross section of it.Gain settings should be at reference level and the probe

should be moved very slowly when examining signalcharacteristics. When looking at indication signals, thefollowing questions should be asked:• Is the signal clean and sharp or is it jagged?• What happens when the probe is skewed? Does thesignal immediately drop away or does it remain?

• What happens when you move the probe towards andaway from the discontinuity?

• What angle responds best?• Are there multiple peaks?

• Are there trailing echoes?• Are there tip-diffracted signals?

Indications Caused by Geometry

Indications caused by the weld root or weld cap are easy todetermine by plotting alone. Another common situationfrom both the weld root and the weld cap is illustrated inFig. 2a. Point A occurs when a signal is returned from theroot. Point B produces an indication that typically shows upabout half way through the second leg. This is caused bythe beam hitting the root and then reflecting straight up to

A

B

AB

Figure 2. Plots of geometry indications: (a) root and cap;(b) mismatch or misalignment.

(a)

(b)

Figure 3. Slag or porosity: (a) plot; (b) signal characteristics.

(a)B ACD

(b)

Figure 4. Signal for porosity.

FYI continued on page 6.

TNT · July 2013 · 5

the weld cap. This is easily identified because the surfacedistance reading on the discontinuity detector will put it inthe plate on the far side of the weld.In the case of a mismatch (Fig. 2b), there will be an

indication from the weld root geometry from one side ofthe weld (plot A) and not the other (plot B). Withmisalignment, the weld root indication will be visible fromone side of the weld for half the circumference of a pipe orvessel and from the other side of the weld on the otherhalf.

Slag

Plot. Depending on the location, slag will plot in the firstand second legs (usually in the body of the weld) andshould show volume (Fig. 3a). It can sometimes be seenusing a 0 degree probe from the weld cap surface. If it plotsdirectly in the centerline, signal characteristics becomecritical; it could be a centerline crack.Signal Characteristics. Signal characteristics can be low inamplitude and will usually have a small trailing echo, verysimilar to one produced by side drilled holes. The signalusually drops off relatively quickly when the probe isskewed.

Porosity

Plot. The plot for porosity is similar to slag (Fig. 3a).Signal Characteristics. Signal characteristics for porosity areusually a low-amplitude, wide, hashy signal that will remain,or walk when the probe is skewed. Porosity can appear asmultiple signals as well. Porosity is probably the easiestdiscontinuity to miss. Discontinuity detection scans shouldbe conducted 12 dB hot for this reason (Fig. 4).

Centerline Crack

Plot. Centerline cracks will plot the same as slag andporosity (Fig. 3a) except the plots from each side of theweld should be closer together, indicating a narrowerdiscontinuity.Signal Characteristics. The signal for a centerline crack willlikely appear rough and be wider than slag but can besimilar to porosity (Fig. 5). When the probe is skewed, thesignal will remain and walk a little. Signal discrimination andfinite plotting are vital in distinguishing the differencebetween porosity and sidewall cracks. Porosity usuallydisplays more peaks than a crack.

Lack of Sidewall Fusion (LOSWF)/Sidewall Crack

Plot. As seen in Fig. 6a, lack of sidewall fusion or sidewallcracks should plot in the second leg from the same side thatthe discontinuity is on (plot A). When looking in the firstleg from the same side (plot B), it is typically not visible,although a 70 degree probe can sometimes get a very smallsignal. Occasionally, when looking from the first leg on thesame side, a signal will be received that plots out similar toplot B1. This happens when the beam hits the lack offusion and bounces straight down to the bottom surface ofthe plate (plot B2). From the opposite side of the weld, itwill not be visible in the second leg and will only be visible

Figure 5. Signal for centerline crack. Figure 6. Lack of sidewall fusion: (a) plot; (b) signal.

(a) ABC

B1

B2

(b)

FYI continued on page 8.

FYI continued from page 5.

6 · Vol. 12, No. 3

from the first leg if the lack of sidewall fusion is lowenough toward the weld root (plot C).Because the surface of a sidewall crack is rough and

faceted, it is probable that the signal will be picked up fromsome or all of the locations where lack of sidewall fusioncan’t be used.LOSWF Signal Characteristics. Lack of sidewall fusionshould be the discontinuity that is easiest to identify. Thesignal is usually very high in amplitude and very clean andsharp (Fig. 6b). Also, when the probe is skewed, the signalimmediately drops straight off instead of walking a little.Because bevels are usually around 30 degrees, the sound

beam reflector will typically respond best to 60 degrees (thisplaces the beam at 90 degrees to the discontinuity).Sidewall Crack Signal Characteristics. The signal forsidewall cracks will likely appear rough and be wider thanlack of sidewall fusion. When the probe is skewed, thesignal will remain and walk a little. As with lack of sidewallfusion, the signal is typically high in amplitude and respondsbest to 60 degrees.

Root Cracks and Lack of Root Fusion (LORF)

Plot. Root cracks and lack of root fusion will plot in theroot area on one side of the root (Fig. 7a). It is important toplot from both sides of the weld when possible because theplots should show that the discontinuity is on the same sideof the root and that it is narrow.Signal Characteristics. Signal characteristics are thedistinguishing factor between root cracks and lack of rootfusion, although discerning the difference can still bedifficult. However, most performance demonstration testsand the ASME code only require the ability to distinguishplanar discontinuities from volumetric discontinuities. Withcracks, the facets of the cracks are usually visible along witha tip diffracted signal and when the probe is skewed, thesignal will remain longer than the signal for lack of rootfusion. The reflector signal will also have a wider base thanlack of root fusion. Lack of root fusion characteristics will

Figure 7. Root crack or lack of root fusion: (a) plot; (b) signalfor root crack; (c) signal for lack of root fusion.

(b)

(c)

(a)AB

Figure 8. Lack of root penetration: (a) plot; (b) signal.

(b)

(a)AB

FYI continued from page 6.

FYI continued on page 10.

8 · Vol. 12, No. 3

TNT · July 2013 · 9

Across4. This type of reference block is easily transported in thefield.

6. Measurement unit of sound energy.7. Sound ____ traveled at anangle from transducer exitpoint to discontinuity.

10. Description of raster scantransducer sequence.

14. A ___________ waveexamination of the parentmaterial on each side of theweld is the primaryexamination prior to anglebeam examination of theweld.

16. Incomplete bonding of theweld metal to the side ofthe original weld groove iscalled sidewall lack of______.

19. Area of weld where lack ofpenetration occurs.

21. __________ in the parentmaterial could alter thesound path.

Down1. Weld _____; a pre-inspection requirement for drawingweld plot.

2. Imaginary line along the longitudinal direction of weld.3. The velocity of shear wave propagation is approximately____ the velocity of compression wave propagation.

5. Distance along surface equivalent to one full V path.8. This kind of crack is located where the crown of theweld meets the parent material.

9. Description of crack at right angle to longitudinal axisof the weld.

11. In a longitudinal soundwave, particle motion isclassified as being in twozones, either___________ orcompression.

12. Category of discontinuitythat includes porosity andslag.

13. Category of discontinuitythat includes cracks andlack of fusion.

15. Description of thetransducer movement toand from the weld.

17. Area of weld where slag isusually detected.

18. Wave mode of ultrasonicpropagation usuallyapplied to ultrasonic weldexamination.

20. Area adjacent to weldaffected by heat.

Answers

CrosswordChallengeU l t r ason i c Tes t i ng o f We ldsU l t r ason i c Tes t i ng o f We lds

CrosswordChallenge

1

4 5

6

7 8 9

10 11

12 13

14

15

16

17

19

20

21

18

2 3

Across4.DSC6.decibel7.path10.overlap14.compression

16.fusion19.root21.laminationDown1.width2.axis

3.half5.skip8.toe9.transverse11.rarefaction12.volumetric

13.planar15.scanning17.body18.shear20.HAZ

be similar to lack of sidewall fusion but can be rougher andwalk a little more.

Lack of Root Penetration (LOP)

Plot. Lack of root penetration will plot on each side of theroot (Fig. 8a) and is typically visible with a 0 degree probefrom the weld cap surface.Signal Characteristics. The signal for lack of rootpenetration typically has a wide base and is high inamplitude. Its signal usually persists briefly when the probeis skewed.

Conclusion

A contour gauge and careful plotting, followed by thedetailed discrimination of signal characteristics, willdetermine the location and reveal the identity of adiscontinuity. Additionally, if the proper training pieces aremade available to technicians and the steps recommended inthis text are followed, the results of industry performancedemonstration tests, as well as the quality of work done inthe field, should show commensurate improvement.

10 · Vol. 12, No. 3

FYI continued from page 8.

TNT · July 2013 · 11

Q. I have an ultrasonic inspection question about accuracy andbest performance when I check in the middle of a flange of anIPE (medium size flange I-beam manufactured according toEuronorm 19-57 standard) or HEA (European acronym forwide flange I-beams) girder. Is this signal of flaw true or whatis the percent of error in this measurement? Thanks for yourhelp. GAV.

A. This is a question that you need ask your Level III, as Ido not know the exact configuration of the material youare inspecting. However, based on personal experience, ifthe welds you are inspecting are on typicalbeam-to-column flange connections as shown below, copeholes are often cut in the end of the beam web beneaththe upper flange weld to allow the insertion of a backingbar, and above the lower beam flange to allow the welderaccess to weld the area in the center of the flange. Whentesting such weld configurations, it is possible to movethe transducer back far enough from the weld so that thesound beam picks up the edge of the cope hole (point Ain Fig. 1). This will often result in a very large signal onthe CRT (cathode ray tube) screen at a sound path similarto that of a large root reflector. There are two ways todetermine if this signal is a cope hole reflector. First, ifyou calculate the sound path versus the surface distance(from the transducer exit point to the weld), you will seethat the surface distance is too great for the reflector tobe in the weld. Second, you can see if the signal can bedamped using a couplant-wet finger. In the dampingprocess, you maximize the signal on the screen andreduce the gain until the top of the signal is on thescreen, then wet a finger and tap the junction of the copehole and the flange (point A) with that finger. If that isthe point where the signal originates, some of the soundwill travel into your wet finger, reducing the sound

returning to the screen signal and lowering the amplitudeof the signal. When you remove your finger, the signalshould go back to the original screen amplitude. Tappingpoint A should cause the amplitude to bounce up anddown in time with the tapping, indicating that this is thesource of the return signal, which is an irrelevant signalcaused by part geometry.

Again, your Level III should be able to demonstrate thisprocess to you and is the person that should confirmthat the signal is irrelevant.

Q: I am a military veteran and would like to know if the ASNTexaminations are approved for GI Bill reimbursement, and ifso, how do I go about applying for it? A.W.

A: Yes, ASNT NDT Level III and IRRSP examinations haveall been approved by the Veterans Administration forreimbursement. Eligibility requirements can be foundonline at www.gibill.va.gov/resources/education_resources/programs/licensing_and_certification.html. On that page under How to Find ApprovedLicense & Certification Tests, you can click on the Searchfor approved tests link and the WEAMS (Web EnabledApproval Management System) search page will come up.To find the ASNT NDT Level III exams, select LACCategory Type as either Certification or Both, leave theL&C Name block empty then click on Ohio on the map(ASNT is located in Ohio), which will bring up the list oflicensure and certification programs that have beenapproved by the Ohio Department of Education for VAreimbursement. Clicking on Non Destructive Testing NDTLevel III will bring up our ASNT NDT Level III examsand clicking on Industrial Radiography Radiation SafetyPersonnel will bring up our IRRSP exam information.Reimbursement is currently $250.00 per examination.

According to the VA's L&C pamphlet, you are eligiblefor reimbursement if you qualify for the Montgomery GIBill (MGIB or MGIB-SR), the Reserve EducationAssistance Program (REAP), the Veterans EducationalAssistance Program (VEAP) or Dependents EducationalAssistance (DEA). The Veterans Administration asks thatyou submit your reimbursement request within one yearof when the test was taken.

Respectfully,James W. Houf,Senior Manager, ASNT Technical Services DepartmentE-mail, fax or phone questions for the “Inbox” to theEditor: hhumphries@asnt.org, fax (614) 274-6899,phone (800) 222-2768 X206.

INBOX

Figure 1. Cope hole reflector.

WebCope holes

Point A

Beam flange

Beam flange

Column flange

the NDT Technician

Volume 12, Number 3 July 2013

Interim Publisher : Betsy Blazar

Publications Manager : Tim Jones

Editor : Hollis Humphries

Technical Editor: Ricky L. Morgan

Review Board: W illiam W. Briody, Bruce G. Crouse,Anthony J. Gatti Sr., Edward E. Hall, James W. Houf, JocelynLanglois, Raymond G. Morasse, Ronald T. Nisbet, AngelaSwedlund

The NDT Technician: A Quarterly Publication for the NDT Practitioner(ISSN 1537-5919) is published quarterly by the American Society forNondestructive Testing, Inc. The TNT mission is to provide informationvaluable to NDT practitioners and a platform for discussion of issuesrelevant to their profession. ASNT exists to create a safer world by promoting the profession andtechnologies of nondestructive testing.Copyright© 2013 by the American Society for Nondestructive Testing, Inc. ASNT isnot responsible for the authenticity or accuracy of information herein. Publishedopinions and statements do not necessarily reflect the opinion of ASNT. Products orservices that are advertised or mentioned do not carry the endorsement orrecommendation of ASNT.

IRRSP, Materials Evaluation, NDT Handbook, Nondestructive Testing Handbook,The NDT Technician and www.asnt.org are trademarks of The American Society forNondestructive Testing, Inc. ACCP, ASNT, Level III Study Guide, Research inNondestructive Evaluation and RNDE are registered trademarks of the AmericanSociety for Nondestructive Testing, Inc.

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