3/3 template (cfoweb) - asnt ndt library

TTNNTTThe NDT Technician A Quarter ly Publ icat ion for the NDT Pract it ioner

M ost products used in drilling oil wellsare made of ferrous steels and aretherefore inspected with magnetic

particle and electromagnetic methods. Thisarticle, excerpted from Volume 2 of theNondestructive Testing Handbook on LiquidPenetrant Testing describes the novelapplication of liquid penetrant testing in oilfielddrill pipe when typical methods aren’tapplicable.

Range of Applications

Some tubular products used in drilling are madeof austenitic stainless steels or beryllium copperand are not magnetic in nature. These parts arenormally used in directional survey or otherapplications where a magnetic field interfereswith the results to be obtained.

These tubulars normally fall into the categoryof bottom hole assembly (BHA) components.This assembly is used to put weight on the bit sothat it will break up the formation as it rotates.The tubulars have large outside diameters andminimal inside diameters to maximize weight onthe bit and stability. The cross section of thenonmagnetic tubular shown in Fig. 1, is 7.75 in.(200 mm) outside diameter and 2.8 in. (70 mm)inside diameter.

During use, the nonmagnetic bottom holeassembly components develop cracks because offatigue and stress corrosion. Fatigue cracksoriginate in the thread roots because this is theweak point for cyclic stress. The cyclic stress iscaused by the rotation of the bottom holeassembly while it is bent from compression or ina dogleg. Stress corrosion cracking originatesfrom the bore of the nonmagnetic bottom holeassembly (Fig. 1). Stress corrosion cracking iscaused by a combination of stress and corrosion.These cracks can be either longitudinal ortransverse.

CleaningSteam cleaning is the method of choice forcleaning bottom hole assembly components. Theheat both opens the cracks and makes thethread lubricant less viscous. For this system towork the cleaning must be done with sufficienttime to warm up both the bottom hole assemblymaterial and any thread lubricant.

If steam cleaning is not available, solvent isthe next choice. Solvent can also be used aftersteam cleaning to remove the detergent residue.The final cleaning solvent should be one thatthe liquid penetrant manufacturer has deemedcompatible. Residues from cleaning agents,strong alkalies, pickling solutions and chromatemay adversely react with the liquid penetrantand reduce sensitivity and performance.

Liquid Penetrant Testing TechniqueSelection

Visible dye liquid penetrants are used to inspectnonmagnetic bottom hole assembly materials.Visible dyes provide the required sensitivity forthe type and size of cracks found innonmagnetic bottom hole assemblies.Nonmagnetic bottom hole assemblyconnections are inspected many times in their

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Volume 3, Number 3 July 2004

Focus: Liquid Penetrant Testing of Oil Field Drill Pipe . . . . . . . . . . . 1

Tech Toon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

TNT Crossword: Ultrasonic Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

FYI: Practical Contact Ultrasonics — IIW Based Angle Beam

Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Feature: Airport Inspection Systems from an NDT Perspective . . . . 8

Working Smarter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Practitioner Profile: Jacob D. Weerts . . . . . . . . . . . . . . . . . . . . . . . . 11

A Publication of the American Society for Nondestructive Testing

FocusLiquid PenetrantTesting of Oil FieldDrill Pipeby Joseph L. Mackin

CONTENTS

TTNNTT

Figure 1. Cross section of nonmagnetictubular from bottom hole assembly.

The NDT Technician A Quarter ly Publ icat ion for the NDT Pract it ioner

Continued p 2.

2 · 07/2004 · The NDT Technician

Tech Toon

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FROM THE EDITOR

T he Focus article for this issue of TNT is anexcerpt from the Liquid Penetrant Testingvolume of the third edition Nondestructive

Testing Handbook series. The article details PT asapplied to tubular parts used in drilling oil wellswhen typical methods are not applicable. This is anovel or unusual application of the method and,consequently, may provide insight for otherindustries using similarly constructed equipment.

The FYI Practical Contact Ultrasonics seriescontinues with article four in the projected series ofeight and encompasses procedures for IIW basedequipment calibration.

This issue also includes a feature article onairport inspection systems. It’s is an eye openingoverview given by an industry expert from an NDTperspective. Considering the difficulty andmagnitude of the task, it encourages patience andcooperation by and for all those traveling by air.

Hollis HumphriesTNT Editor

PO Box 28518, Columbus, Ohio 43228(800) 222-2768 X206; fax (614) 274-6899

<[email protected]>

life and because it is not advisable to usefluorescent liquid penetrant after visible dyeliquid penetrant, the use of fluorescent is avoided.

Liquid penetrant used to inspect the threadedarea is normally removed by the solvent wipetechnique. Water washable liquid penetrant is notappropriate because restricted access to the boxthreads makes it difficult to remove excess water.

Water washable liquid penetrant is mostappropriate for the small inside diameters of thebore. Water washable liquid penetrant is alsoused for outside diameter surfaces.

Test Process

Temperature. Surface temperature is typically thebiggest problem in testing oil field equipment.The range of acceptable temperatures for liquidpenetrant testing is 50 to 125 °F (10 to 52 °C). It isimportant that the temperature remain withinthis range throughout the testing process.Because most of these tests are done in the field,the inspector has little control over theenvironment. If steam cleaning is done, thebottom hole assembly must be allowed to cool toan appropriate temperature. In the winter whiledoing the testing outdoors, the bottom holeassembly may be too cold to do a reliable test. Inthis case the bottom hole assembly must bemoved inside and allowed to warm up beforetesting. It is important that the surfacetemperature remain within the proper rangeduring the entire test time.

The bottom hole assembly temperature is themain consideration for dwell time. As thetemperature approaches the minimumtemperature of 10 °C (50 °F) the dwell time shouldbe extended to 30 min. Longer dwell times do notaffect the sensitivity of the test as long as theliquid penetrant is not allowed to dry. So, if indoubt, extend the dwell time.Removing Excessive Liquid Penetrant. Standardliquid penetrant removal procedures are used forthe removal of both the postemulsifiable andwater washable liquid penetrants. When liquidpenetrant is removed with a solvent wipe, atechnique for both the dry wipe and damp wipeshould be developed so that the minimumnumber of passes over the surface are required tothoroughly clean the surface. Ideally, if all theexcessive liquid penetrant could be removed withone pass of the dry cloth and one with thedampened cloth the optimum result for the testwould be achieved.Drying. Surfaces of the bottom hole assembly tobe inspected must be completely dry before theapplication of the developer. With the solventremover system, this is not normally a problem,because the solvent dries quickly.Developer Application. Solvent based(nonaqueous wet developer) spray-on developeris normally used in the testing of bottom hole

“Looks like a shear horizontal wave to me, Murph.”

Focus continued from p 1.

Across

2. Increases strength of signal.4. Periodic disturbance in a

medium.7. One crystal, transmit and

receive (3 words)9. Longitudinal pressure waves

in air or some medium.10. _______ beam, split crystals.

11. Frequencies within audiblerange.

14. Type of battery(abbreviation).

15. International Institute ofWelding.

16. Difference between twopoints on a conducting wirecarrying a constant current ofone ampere when powerdissipated is one watt.

18. Cathode ray tube(abbreviation).

20. Distance being displayed onCRT screen.

21. Increase in signal power withdBs.

22. One type of ultrasonicinspection.

23. Sound area other than insound path.

25. Returning sound.26. Type of crystal.31. Defect shows lack of _______

(see figure below left).32. Couplant.35. Transmitter and _______.36. λ – b.37. Illuminated line on CRT

screen.38. Controls pulse repetition rate.

Down

1. Graduation of an instrumentto enable measurements indefinite units.

3. Number of cycles per secondundergone or produced by

an oscillating body.4. Substance which lowers

surface tension of a liquid.5. Document which prescribes

approved procedures to befollowed.

6. Hz.8. When a system vibrates at

the same frequency as theexciting force, it is said to bein _______.

10. dB.11. Ability of the test system to

detect a given sized defect ata given distance.

12. Used to insure passing ofsound waves into and out ofspecimen.

13. See 37 across.16. N = D2F / 4C, where C is the

_______ of sound.17. Transducer or search unit.19. Moderately damped probe.23. Transfer _______ caused by a

rough or curved surface.24. Larger diameter probe will

give you less _______ spread.27. Some transducers have a

dead _______.28. Ten decibels equals one

_______.29. Opposite of bright.30. In formula in 16 down, N is

_______ field.33. Frequency that oscillates

between 10 kilohertz to100,000 megahertz.

34. Nondestructive testing(abbreviation).

07/2004 · The NDT Technician · 3

assembly threaded areas. This, of course, isdifficult in rotary shouldered connections,particularly the box, because the restricteddiameter makes it difficult to spray directly onthread roots. However, achieving an even thincoating on the thread roots should beemphasized as that is where cracks will belocated.

For the inside and outside diameter surfacesdry powder developer is also used.Evaluation. The area to be inspected should beobserved periodically during the developmenttime. In the evaluation process, the observationsmade concerning indication development willbe helpful. The test should be done with at least500 lx (50 ftc) light intensity at the surface to be

inspected. The final examination is only doneafter the full development time has elapsed.Figure 2 shows crack indications on theconnection outside diameter after thedevelopment time.

Regardless of size, cracks render a bottomhole assembly unfit for service and it must berejected. Other indications are classified accordingto the appropriate testing standard. TNT

An active member of ASNT since 1989, Joseph L.Mackin is the current President of ASNT. He isalso Executive Director of the International PipeInspectors Association (IPIA), Houston, TX. Heholds ACCP Professional Level III certifications inMT, PT, UT and VT and ASNT NDT Level IIIcertification in ET.

Figure 2. Crack indications on connectionoutside diameter after development time.

Crossword Ultrasonic Testingby Jacques L. Brignac

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Answers on p 10.

T he most critical task prior to starting acontact angle beam ultrasonicinspection is the UT operator's

calibration of the UT equipment with respect tothe specific part to be inspected. The termcalibration in UT is applied to both annual scopecalibration and on site or field calibration.Annual calibration determines that the scopemeets horizontal and vertical linearityrequirements and can be done in house by aLevel III or externally by a qualified UTequipment supplier. On site calibration using theIIW block or derivatives, the focus of this article,is performed by the UT operator at the time ofthe inspection and consists of setting up thescope presentation and sensitivity of theinspection unit to perform a specific inspection.

The two most commonly used UT calibrationmethods in the US are based on either theInternational Institute of Welding (IIW)calibration block or a derivative that theAmerican Society of Mechanical Engineers'Boiler and Pressure Vessel Code (ASME Code)refers to as a basic calibration block.

The IIW Block

IIW calibration blocks are 12 × 4 × 1 in. in sizeand are made of the same or acoustically similarmaterial as the part to be inspected.Predominant features of an IIW block, Type 1(Fig. 1), are two side drilled holes that are 0.06and 2 in. in diameter and two notches. The firstnotch is a 0.06 in. deep curved notch with aninner radius 1 in. from the marked referencepoint and another 0.08 in. full width notchdirectly opposite the reference point. One endof the IIW block is cut to a 4 in. radius from thereference point. For illustration purposes,additional etched markings located on the longedge of the block have been shown on thesame side or front of the block in Fig. 1.

The IIW block is designed to permit theoperator to perform multiple functions for bothstraight and angle beam testing includingdistance and sensitivity calibration and wedgeangle verification. For straight beam calibration,the transducer can be placed on the 1 in.surface at the reference point and the screenwidth can be set by using the 4 in. reflectionfrom the opposite side. Block thickness can be

used for 1 in. reflections. Because the referencepoint is directly opposite the 0.08 in. notch,resolution can also be determined.

Wedge Angle Verification

For angle beam testing, the wedge angle can bechecked by placing the transducer on the 1 in.surface at point A in Fig. 2. In this example, a70 degree point (shown on the side of thewedge) is placed over the 70 degree marketched on the side of the block. The transduceris then moved back and forth until the returnsignal from the 2 in. diameter hole is maximizedon the cathode ray tube (CRT) screen. The actualrefracted angle can be read by determiningwhere the exit point mark aligns with markingson the side of the block. When using 45 or60 degree probes, the operator starts with thetransducer over the corresponding mark on theblock and checks the wedge angle in the samemanner. It should be noted that most codes andspecifications permit the wedge angle to varyslightly within ±2 degrees of the designatedangle, but the the tolerance should be verifiedbefore continuing. If the wedge angle is within

tolerance, the operator can proceed to distancecalibration or setting screen width.

Distance Calibration

To set up a CRT screen width that represents theproper distance for the part being tested, theoperator must determine the length of thesound path in that thickness of material, as wasdescribed in the previous article. Once thelength of a full skip distance is calculated, thescreen width can be set. In the followingexample we will set up a 10 in. screen.

Prior to starting the distance calibration,good operating procedure is to make sure theelectrical zero, or main bang, is at or just off theleft edge of the CRT screen. If not, it is possiblethat the operator will be working with thesecond reflection, which makes it impossible tocalibrate the machine. A simple way todetermine this is to dampen a finger withcouplant and rub the bottom of the transducerface. The resulting signal can be set to the leftside of the screen.

Once the operator is comfortable that themain bang is in the right place, the transducer isplaced on the 1 in. block surface above themarked reference point (placement B, Fig. 2)and is aimed at the end of the block with the4 in. radius. Using the range and delay controls(may be named differently on newer machines,see manual), maximize the signal from the 4 in.radius and set the reflector signal at the fourthmajor graticule on the CRT screen. Then turnthe transducer around and maximize the returnsignal from the curved notch with the 1 in.radius. Set that signal at the first majorgraticule. For smaller diameter transducers, itmay be necessary to move the transducer to the

FYIPractical ContactUltrasonics — IIW BasedAngle Beam Calibration

by Jim Houf

Side drilled holes Full width notch

Curved notch1 in. radius

45º60º

70º

Reference point

2 in. 4 in. radius

0.06 in.0.08 in.

Figure 1. International Institute of Welding (IIW) calibration block, Type 1.

BA

C

70º

Figure 2. Transducer placement on IIW calibration block, Type 1.

LegendA. Wedge angle.B. Distance calibration.C. Sensitivity calibration.


SignalSignal

Signal


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side of the 1 in. surface to get a good signalback from the radiused notch. Switching backand forth between the two transducerpositions, the operator should continue toadjust the controls until both signals line up onthe proper graticules. When this isaccomplished, screen width is set to 10 in. witheach major graticule representing 1 in. of soundpath.

Sensitivity Calibration

Sensitivity calibration is done to provide aninspection reference level based on theamplitude (height) of a signal from a reflectorof a known size. On the IIW block, that signal isgenerated from the 0.06 in. side drilled hole. Toset sensitivity, the block is turned over and thetransducer is placed on the 1 in. surface inboardof the 0.06 in. side drilled hole (placement C,Fig. 2). The transducer is moved back and forthuntil the signal from the hole is maximized onthe CRT screen. Using the gain control, thesignal amplitude is then adjusted so that themaximized signal is set at 80 percent of fullscreen height (FSH). The amount of gain indecibels (dB) is recorded and this gain valuebecomes the reference level for inspection.

Note that 80 percent FSH is commonly used, butsome codes and specifications may requireother FSH values.

Once the UT system has been calibrated, theoperator can increase the gain setting to thescanning level (dB value) dictated by thegoverning code or specification and performthe inspection.

Alternative Calibration Blocks

While the IIW block is a very good calibrationblock, its large size and heavy weight areinconvenient when carried in the field or whenworking out of position and up in the air.Several other calibration blocks have beendesigned that are smaller and lighter in weight.Distance Sensitivity Calibration Block. The mostcommonly used alternative block is the distancesensitivity calibration (DSC) block (Fig. 3). TheDSC block measures 4 × 1 × 2.5 in. which isconsiderably smaller and lighter than the IIWblock and will fit into a pocket. This block has aflat scanning surface with a 1 in. radius at oneend and a 3 in. radius at the other end. The 3 in.end of the block has a machined 0.375 in. deep,0.031 in. wide flat bottomed notch with a2.625 in. radius from the reference point.

Manufactured commercially, these blocks can bepurchased from many UT suppliers.

When using a block that has a radius on bothends, it is important to remember that most of asound beam will reflect from an interface, sowhen the sound reflects from the 1 in. radius,most of the sound returning towards thetransducer will reflect from the scanning surfaceand travel down towards the 3 in. radius. Thissound will then return to the scanning surfacebut since it hits the scanning surface at thewrong angle to enter the probe , it reflectsdownward towards the 1 in. radius and then

Continued p 6.

Figure 3. Distance sensitivity calibration(DSC) block is a smaller and lighter alternativeto heavier reference blocks.

Reference point

1 in.radius

0.125 in.

3 in. radius

0.375 in.

2.5 in.

0.031

1 in.


returns to the transducer, creating a secondsignal. As a result, it is important to note thatthe distance between the back wall signals is thesum of the distances from the radii to thereference point and the second back wall (andall others) will show on the screen at 4 in., thesum of 3 + 1 in., after the preceding back wall.

To perform a distance calibration for a 5 in.screen, the transducer is placed at the referencepoint and aimed at the end with the 1 in.radius. The first return signal is maximized andplaced on the second major graticule. Twoadditional signals should be on the screen; ashort signal from the notch and a taller signalfrom the 3 in. radius. The signal from the 3 in.radius should be placed on the tenth majorgraticule and using the delay and rangecontrols, the 1 in. and 3 in. signals should beadjusted until both fall on the proper graticule.When this is done, the scope should be set for a5 in. screen. The signal locations arerepresented by the green signals shown on the5 in. screen (Fig. 4a). To confirm calibration, thetransducer is reversed and aimed at the 3 in.radius. If calibration is correct, the first signal onthe screen will be the notch (just past the fifthgraticule) and the next will be the 3 in. radiussignal (sixth graticule). These positions areshown by the signals shown in purple on the5 in. screen presentation (Fig. 4a). As mentionedabove, since the signal from the 1 in. radiusoccurs 4 in. later, it would come up at 7 in.,which cannot be seen on a 5 in. screen.

To perform a distance calibration for a 10 in.screen, the transducer is again placed at thereference point and aimed at the end with the1 in. radius, but this time the first return signalis maximized and placed on the first majorgraticule. Because the distance between backwalls is the sum of the radii, the operatorshould also see back wall signals at 5 in. and9 in., with notch signals 0.375 in. before eachback wall signal, shown in green in the 10 in.screen presentation (Fig. 4b). Again, the delayand range controls should be used to positionthe back wall signals in the proper places. Toverify calibration, the transducer is againreversed and aimed at the 3 in. radius. Theoperator should then see back wall signals at3 in. and 7 in., with notch signals slightly beforeeach back wall signal (signals shown in purpleon 10 in. screen presentation in Fig. 4b).

In either calibration, if the second set ofsignals (shown in purple) do not come up onthe screen where they should be, the operatorshould use the delay control to determine thatthe main bang is where it should be (at or offleft side of screen). If not, and if a first back wallis at that location, move the main bang to theleft edge of the screen and start over.

Sensitivity calibration using a DSC block isperformed in the same manner for either a 5 or

10 in. screen. Once screen width has been set,the transducer is aimed at the 3 in. radius andthe signal from the notch is maximized and setto 80 percent full screen height (or as detailedin governing documents). The gain setting forthis signal amplitude is used as the referencelevel for the inspections. When using a 10 in.screen, there will be two notch signals, at screenlocations of 2.625 in. and 5.25 in. The 2.625 in.signal should be set to 80 percent FSH (or asrequired), and if the operator is permitted to doso, peaks of the two signals can be connectedto create a rudimentary distance amplitudecorrection (DAC) curve.

There is a correlation between the IIW blockand the DSC block. The signal amplitude fromthe notch of an accurate DSC block should bewithin ± 2 dB of the signal created by the0.06 in. side drilled hole in the IIW block, andthis should be checked at regular intervals.Distance Calibration Block. The distancecalibration (DC) block (Fig. 5a), often called a1-2 block, is similar in shape to the DSC block buthas a 1 in. radius and a 2 in. radius. It does nothave a notch for sensitivity calibration. For thisreason, distance calibrations can be performedbut the operator must carry a separate block toset the sensitivity level of the equipmentHalf Round Distance Calibration Block. AnotherDC block is the half round block (Fig. 5b). Likethe 1-2 block, it can be used for distancecalibration but a separate sensitivity block is

required. The advantages to the half roundblock are that that they can be readilymanufactured by any machine shop and, byusing various radii, very narrow screen widthscan be set up.IIW Hit Block. The IIW hit block is a smallportable sensitivity calibration block that is a1 in. thick piece of material representing thecorner of the IIW block that contains the0.06 in. side drilled hole. The block is4 × 2 × 1 in. with an 0.06 in. side drilled hole0.6 in. down from the 1 in. scanning surface and1.4 in. in from the end of the block (Fig. 6). Byusing the hit block and a DC block mentionedearlier, calibration for both distance andsensitivity is achieved. Distance is done asmentioned above, and sensitivity is done usingthe hit block in the same manner as is done ona full size IIW block. TNT

Jim Houf is Senior Manager of ASNT’s TechnicalServices Department and administers all ASNTcertification programs. (800) 222-2768 X212,(614) 274-6899 fax, <[email protected]>.

Figure 5. Distance calibration (DC) blocksrequire separate sensitivity blocks:(a) 1–2 block and (b) half-round block.

Reference point

2 in.

1 in.

0.5 in.

0.5 in.

0.5 in.

2 in.

1 in.

(a)

(b)

Figure 4. Signals resulting from distancecalibrations performed on DSC block for(a) 5 in. screen and (b) 10 in. screen.

1 in. signal

Notchsignal

3 in.signal

3 in. signal

3 in. + 1 in. signal

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FYI continued from p 5.

Figure 6. The IIW hit block is a small portablesensitivity calibration block representing acorner of the IIW block.

1 in.

1.4 in.

4 in.

2 in.0.06 in. diameter hole

0.6 in.

ASNT is an International System of Units (SI)publisher providing units in SI as well ascommon units of measure.

1 in. = 2.54 cm

I f you’ve traveled at all by air in the pastfew years, you’ve experienced theextensive scrutiny that passengers and

luggage are now subjected to. While standing inlong and often slow airport security lines, theNDT professionals who spend their careerslooking for discontinuities inside items withoutopening them might wonder just exactly whatgoes on in these inspections.

Introduction

Congress established the Transportation SecurityAdministration (TSA) as a means ofstrengthening transportation security after thebombing of the World Trade Towers inSeptember, 2001. As part of the newly createdDepartment of Homeland Security (DHS), thisagency is responsible for security in all modes oftransportation. It’s broad responsibility isorganized into four categories:· commerce inspection systems (luggage, cargo

and mail)· passenger inspection systems (people and

carry on baggage)· infrastructure protection systems (airports,

ports, railroad tracks, bridges, highways, etc.)· aircraft protection systems (includes

hardened and locked cockpit doors incommercial airplanes and specialtransponders).

Inspection Systems

Inspection systems have had a central role inaviation security since the seventies. The firstsystems were metal detector portals screeningpassengers for hidden weapons, and X-raymachines to inspect carry on luggage forweapons. The mandate at the time was tocounter the threat of hijacking. To the NDTcommunity, using X-ray technology as a meansto locate weapons is an obvious solution.Usually made of metal, weapons are thusdetectable with metal detectors. They alsocontrast nicely against the background imageof the mostly organic bag contents and thecarry on bag itself. Also, weapons typically havecharacteristic shapes that are relatively easy tointerpret by the security screener or inspector.Unfortunately, weapons detection has become

much more difficult over time as the metalliccontent of guns and knives has been reduced oreven eliminated completely as in the case ofknives made entirely of a very hard ceramicmaterial. As a result of the escalating threat,metal detection technology and X-ray sensitivityhave greatly improved.

Threat of Explosives

While weapons detection has not been easy,another threat to air transportation has posed amuch more serious challenge to the securitycommunity: explosives hidden in baggage anddesigned to explode while the airplane flies fullypressurized at high altitude. It is at this pointthat aircraft are most vulnerable to break upfrom the sudden overpressure that results whenan explosive detonates. The world of air travelfirst began to seriously consider this threat in1985 when an Air India Boeing 747 explodedover the Irish Sea and disappeared below thesurface of the water. The subsequent criminalinvestigation determined that a bomb had beenplaced on the plane.

The world was shocked again in 1988 whenPan American flight 103 exploded overLockerbie, Scotland a few days before Christmas.This time the plane disintegrated over land andthe location of the bomb as well as its materialcomposition and size could be determined fromthe wreckage. The investigation that followedrevealed another serious concern for securityprofessionals. The amount of sophisticated highexplosive material employed had been verysmall, considerably smaller than had beenassumed up to that point. Potency of explosivesvaries with composition. Certain high explosivesare so powerful that the amount of materialthat can destroy a pressurized fuselage (threatquantity) is so small, it can easily be hidden in asuitcase or carry on bag.

An Explosives Primer

Explosives fall into two major categories; lowand high explosives. Low explosives, such asblack powder, do not truly explode. Instead theyburn very rapidly. Thus, they do not cause thevery high pressure spike that is the mostdestructive feature of an explosion. A low

explosive, to be effective, is placed in acontainer that bursts when the gases from therapidly burning material have built up enoughpressure, causing a severe pressure spike. Suchcontainers (a pipe bomb is an example) arerelatively easy to spot with typical airport X-rayscreening devices, especially since the containerhas to be quite large to accommodate enoughlow explosive material to be effective. It takesconsiderably more low explosive material toachieve the same destructive effect as that ofhigh explosive material. Pound for pound, thedestructive force of high explosives vastlyexceeds that of low explosives.

High explosives do not burn rapidly, theydetonate. Detonation causes a much morepowerful overpressure effect. It also means thatthey are fully effective in bare form, without theneed for an enclosing pressure container.However, high explosives must be set off withanother detonating effect or detonator.

The most powerful explosives are certainplastic explosives. It was a powerful plasticexplosive that destroyed Pan Americanflight 103. Plastic explosives consist of organicmaterial made up of atoms of carbon, oxygen,hydrogen and nitrogen. The vast majority ofhigh explosives contain nitrogen, although thereare some exceptions. Considering theseconstituents, it is readily apparent that plasticexplosives are quite similar to harmless, everydaymaterials. Although to a limited extent, eventheir densities overlap with those of certaincommon, harmless materials. For example, on adensity map, a block of salami falls within therange of densities for plastic explosives.

Screening Checked Baggage forExplosives

To recap, high explosives are organic materialwith the same atomic constituents as manyharmless organic materials. Although difficult tomeasure, there are some characteristicdistinctions at the molecular level. Severalingenious technologies that detect thesedistinctions have been developed or are underdevelopment. However, the sensing processesdeveloped up to now that utilize thesedistinctions are too slow to keep up with theflow of checked luggage. Moreover, they do notwork for all explosives. Thus, the one parameterwe have to work with in high speed screeningfor all explosives is density, even though thisfeature does not distinguish all explosives fromharmless materials.

The problem of screening checked bags forexplosives at a rate of 200 to 800 bags per hourper station before they are loaded onto aircraftcan be framed in terms NDT professionals canrelate to. Subtle density differences have to befound with the greatest possible accuracy andprecision in the content of a container withoutopening it, at a high rate of throughput. The

FeatureAirport InspectionSystems from an NDTPerspectiveby Hans J. Weber



content of a bag consists of many individualpieces with air in between, thus eliminatingtechniques that require material continuitybetween the pieces, such as ultrasonic testing.This leaves X-ray inspection as the method withthe highest level of capability for measuring thevarious densities of the bag’s content. Computedtomography (CT) is the technology with thehighest level of X-ray performance. Indeed, theonly systems that to date have passed stringentTSA certification tests for explosive screening inluggage are those based on CT technology. ATSA certified explosive detection system is calledan EDS. As of April, 2004, only twomanufacturers offer certified explosive detectionsystems. A limited number of manufacturers arepreparing additional systems for TSAcertification. Essentially, the systems currentlycertified are able to discriminate on the basis ofthe three dimensional density distributiongenerated by the CT technique. A furtherrefinement in identifying explosives is achievedby means of highly sophisticated image analysisalgorithms which look for certain patterns in theimage that might further indicate the presenceof explosive devices and help in discriminatingagainst harmless materials of similar density andcomposition.

Despite the use of image analysis algorithms,the density overlap between explosives andcertain harmless materials can result in falsealarms or false positives for CT based explosivedetection systems if the harmless materials arepresent in sufficient quantity. The incidence ratefor false alarms depends on the bag content. Anaverage rate of about 30 percent is not unusual.All alarms must be cleared by determining thecause of the alarm. This can be done by wipingthe bag with a piece of tissue which is theninserted into an explosive trace device (ETD)capable of detecting trace amounts of explosiveswith a high degree of specificity based onmolecular characteristics. Or the alarm can becleared by opening the bag for visual inspection.

As of January 1, 2003, all checked baggagemust be screened for explosives with explosivedetection systems. Inspection with explosivetrace devices or ETDs is acceptable as an interimmeasure until a sufficient number of explosivedetection systems or EDSs have been installed atall airports. Manual inspection is an alternatebut uneconomical inspection method.

Explosive Specific InspectionTechnologies

While ETDs have been found to be effectiveeven if only a modest number of explosivemolecules are present, their effectiveness ishindered by the fact that certain plasticexplosives give off very few molecules in theform of vapor. A skilled and careful terrorist,with the right materials, can theoreticallypackage a bomb and insert it in a bag without

leaving any detectable trace on the outside orinside of the bag. Another drawback of ETDs isthat they are very slow (a few minutes for thefull procedure) and labor intensive.Quadrupole Resonance. Some of thesedrawbacks have been overcome by newertechniques that also discriminate on the basis ofmolecular features. Quadrupole resonance (QR)uses the fact that many explosives emitelectromagnetic radiation at frequencies uniqueto each explosive type after being subjected tobursts of microwave radiation at carefullyselected energy levels. In this sense, quadrupoleresonance behaves like magnetic resonanceimaging (MRI), a powerful, widely used medicaldiagnostic procedure. Unlike MRI, whichrequires powerful magnets surrounding theitem under inspection, QR works with theearth’s magnetic field making it a relativelycompact and simple to use technology. Not allexplosives have been defined in its current stageof development but characteristic signatures forthe most powerful ones and those most likely tobe used by terrorists have been determined.Capture Gamma Rays. Another inspectiontechnique works at the atomic level by exposingthe bag to a beam of fast neutrons and thenanalyzing the characteristic capture gamma raysemitted by oxygen, carbon, hydrogen andnitrogen as a result of the exposure. It has beendemonstrated to be an effective, if expensive,method of detecting explosives with a very lowfalse alarm rate. Neutrons have the furtheradvantage of being able to penetrate readilythrough thick layers of materials. Systemsutilizing this technique have been shown topenetrate large cargo containers and trucks andare thus being considered for cargo inspection.Coherent Scattering. A third techniquediscerning characteristic features of explosivesat the molecular level is coherent scattering.This promising technique looks for explosivesignatures by analyzing radiation scatteredfrom bag contents as a result of incidentgamma rays.

Performance Improvements

Given a false alarm rate that is as high as30 percent for current explosive detectionsystems, the effective throughput of theseinspection machines is determined by the rate atwhich alarms can be cleared. Bag opening formanual inspection or even explosive trace devicescreening is a slow technique, taking more thanone minute per bag. Thus, in an effort toimprove current systems, faster, automatedmeans of clearing alarms are given high priority.Development efforts underway exploreperformance benefits to be gained bycombining an explosive detection system with asystem that is explosive specific, for example aquadrupole resonance based system or oneemploying coherent scattering. A combined

system can be termed as a system of systems. Allbags would first move through the explosivedetection system. Alarms would be screened bya slower secondary system. All nonalarming bagswould be cleared by the explosive detectionsystem. In this approach, the slower secondarysystem would only have to inspect a fraction ofthe total number of bags.

Parallel to the development of combinedsystems, the TSA is encouraging innovativeapproaches using physical principles andtechnologies not yet considered for thedetection of explosives such as advances innanotechnology.

Screening Carry On Baggage

Only a very limited number of carry on bags arecurrently being inspected for explosives. This willmost likely change in the future, as 100 percentscreening is implemented in response to therealization that suicidal terrorists can bringexplosives on board in carry on baggage.Explosive detection systems optimized for carryon bags are under consideration and are clearlytechnically possible. The complexity and cost ofan explosive detection systems decreases ifdesigned for smaller luggage.

Passenger Screening

Passenger screening is still limited to looking forweapons. Various techniques that check forexplosives hidden under clothing are indevelopment. Among these is a phone boothsized device in which air blown over thepassenger is analyzed for trace amounts ofexplosives with explosive trace device typesensors. In another approach, a passengerpauses briefly in a portal and is momentarilysubjected to a very low flux of X-rays. Sensorsembedded in the portal frame receive radiationscattered by the person that is then assembledinto an electronic image. This method has beendemonstrated to reveal the presence of evensmall objects hidden under clothing. Whiletechnically effective, this technique is not yetaccepted for regular use because of unresolvedprivacy issues. The image generated is essentiallythat of an undressed person.

Cargo Inspection

Unfortunately, explosive detection systems forchecked bags cannot be scaled up toaccommodate cargo size items. However, thereare approaches that have demonstrated realpromise such as X-ray systems using an X-raysource with sufficient energy and intensity topunch through the container and its content.The system operates in normal transmissionmode. It can only detect quantities considerablylarger than those specified for checked luggage.

Continued p 10.


Image analysis software also highlightspotential threats. A fast-neutron based systemwhich, in its most sophisticated form, uses anaccelerator to generate pulses of fast neutronswhich are sent through the cargo container.Sensors surrounding the container capture thegamma rays emitted by oxygen, carbon,hydrogen and nitrogen when neutrons interactwith them. The signals are analyzed forcharacteristic signatures indicating the presenceof explosives. Pulsing the neutron beam permitskeeping track of the neutrons and making itpossible to determine the point of origin of the

emitted radiation. This gives the ability to detectsmall quantities on the order of those specifiedfor checked luggage and to pinpoint thelocation of the explosives in the container. Thistechnology is in the prototype demonstrationphase and the cost to implement isapproximately ten times that of an explosivedetection system for checked baggage. TNT

Hans J. Weber is majority owner of TECOPInternational, Inc., a technology managementconsulting group with emphasis on internationalbusiness. He is also owner of Weber TechnologyApplications. He currently serves on the FAA’sResearch, Engineering and Development AdvisoryCommittee (REDAC) as chair of REDAC’sSubcommittee for Aircraft Safety. He also serveson the TSA’s Scientific Advisory Panel.

Across2. Amplifier

4. Wave

7. Single element probe

9. Sound

10. Dual

11. Sonic

14. Nicad

15. IIW

16. Volt

18. CRT

20. Range

21. Gain

22. Weld

23. Lobe

25. Echo

26. Quartz

31. Fusion

32. Glycerine

35. Receiver

36. Lamda

37. Trace

38. Clock

Down1. Calibration

3. Frequency

4. Wetting agent

5. Specification

6. Hertz

8. Resonance

10. Decibel

11. Sensitivity

12. Couplant

13. Trace

16. Velocity

17. Probe

19. Gamma

23. Loss

24. Beam

27. Zone

28. BEL

29. Dim

30. Near

33. Radio

34. NDT

WorkingSmarterCleaning Padded NylonInstrument Cases

F ew people ever clean padded nylon instrument cases but probablywould if they knew just how easy it is. Brush on any good waterlesshand cleaner, inside and outside the case. If absorbed too quickly,

reapply promptly and let sit in a plastic grocery bag overnight to slowevaporation. Then hose down the next day with the garden hose with nozzleattached. Some lanolin will be left on as a residue, which is okay. It will helpfurther cut dirt on the next cleaning and will also keep the nylon soft. Repeatif necessary. Sorry, this won’t remove paint!

Byron MakarwichScorpion Technology

Albuquerque, New Mexico

CrosswordUltrasonic Testing Answers

TNT Crossword appears on p 3.

TNTT

T

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PRACTITIONERPROFILEJacob D. Weerts

J ake Weerts has been working in NDT for almost four yearsnow and he’s really enthusiastic about what he does —pipeline radiography. He says he has lots of active hobbies

— rock climbing, canoeing, spelunking, weight lifting andcooking among them — but just not enough time to be an expertat any one of them.

Q: How did you first become involved in NDT?

A: I was in the welding and machining program at KankakeeCommunity College and the welding instructor started talkingabout NDT. I guess it really struck an interest in me. Two weeks laterI was enrolled full time in NDT. All of my initial training was throughMoraine Valley Community College in Palos Hills near Chicago,Illinois. I completed Moraine’s program and began working parttime for my present employer, McNDT, while finishing college. I’vebeen full time with them for about a year and a half now. McNDT isa pipeline radiography company and I feel like it’s a pretty goodindustry to be in.

Q: What NDT methods do you use most for pipeline inspection?

A: We use gamma radiography and iridium-192 mainly to inspectnew pipeline welds.

Q: Can you describe your work for us?

A: A very large number of the pipelines we work on are forpetroleum and also for natural gas — to and from tank storagefields, to and from refineries, into and out of natural gas powergeneration stations, product delivery lines for, say, jet fuel toairports. Basically, you name it and we’ve done it or can do it. Aphenomenal number of pipelines crisscross the whole country. Theaverage person just doesn’t have a grasp of its magnitude.Something we have specialized in lately is digital or computerizedradiography. Our company has perfected using it to shoot throughfluid filled pipelines. Typically, in the past, if you had a pipeline thatwas, say, 20 in. in diameter, or 24 in. or 12 in., that is full of crude oilor gasoline, you really couldn’t X-ray the line because of the densityof the fluid inside. You couldn’t get the information you needed.Not without taking an exorbitant amount of time to do it. It waspretty much impossible. But with digital radiography you can shootright through fluid filled pipelines. The source used in digitalradiography is exactly the same as film. Any radioactive source youwould use with film, can be used with digital.

Q: So what makes digital radiography different from film?

A: Say you’re shooting a weld with film, you’re going to get acertain density range with film and that density has to beascertained the first time to get it right. Digital is much moresensitive than film. You can effectively shoot the weld in a fraction

of the time because it takes much less exposure. Most importantly,you can read or manipulate the density of the image in areas ofinterest in real time after you’ve captured the image. You can viewalmost any area of interest with just the one shot. The image iscaptured on an imaging plate that is treated just like film. Theproblem with film is, say you’re shooting a casting that has differentthickness of metals, you would have to shoot with either differentspeeds of film to get the right densities or you would have to shooteach area of different thickness separately. This is very timeconsuming and costly. But with digital radiography, you can shoot itwith one shot with one imaging plate and then you can manipulatethe density through the entire range of thicknesses throughout thepiece of material.

Q: What’s been your most unusualapplication of NDT?

A: One thing that I’ve done that’s prettyinteresting is locating something calleda pig. These devices run inside thepipeline on the differential pressuresfrom the fluid in the pipeline. They havedifferent purposes; some clean the pipes— scraper pigs — some inspect.Occasionally, they get stuck or break orget lost. We go in and locate the pig byX-raying areas of the pipeline. It’s kindof fun finding the needle in thehaystack.

Q: What’s the worst part of NDT

A: I don’t want to sound really spoiled saying this because I don’thave to do this on a regular basis but I guess that would be workingon a holiday or a weekend in the middle of the night, in a powerstation, inside a boiler. It’s not fun.

Q: What’s the best part of NDT?

A: Pipeline work. My work is great. It’s challenging to work asefficiently as you can work especially if there’s a rush. Beingoutdoors, working in an open area is very appealing to me. I likethe fact that you’re traveling on a mainline job and going to seesome new places and new things.

Q: What advice would you offer to someone considering a careerin NDT?

A: A degree doesn’t hurt. Avoid being complacent, pursueadditional training and maintain your certifications. It’s alsoimportant to maintain a well put together resume. Document yourwork history. TNT

Volume 3, Number 3 July 2004

Publisher: Wayne HollidayPublications Manager: Paul McIntire

Editor: Hollis HumphriesTechnical Editor: Ricky L. Morgan

Review Board: William W. Briody, Bruce G. Crouse,Ed E. Edgerton, Anthony J. Gatti Sr., Jesse M. Granillo,Edward E. Hall, Richard A. Harrison, James W. Houf,Eddy Messmer, Raymond G. Morasse, Ronald T. Nisbet

The NDT Technician: A QuarterlyPublication for the NDT Practitioner(ISSN 1537-5919) is published quarterlyby the American Society forNondestructive Testing, Inc. The TNTmission is to provide information valuableto NDT practitioners and a platform fordiscussion of issues relevant to theirprofession. ASNT exists to create a safer world by promoting the professionand technologies of nondestructive testing.

Copyright © 2004 by the American Society for Nondestructive Testing, Inc.ASNT is not responsible for the authenticity or accuracy of informationherein. Published opinions and statements do not necessarily reflect theopinion of ASNT. Products or services that are advertised or mentioned donot carry the endorsement or recommendation of ASNT.

IRRSP, Level III Study Guide, Materials Evaluation, NDT Handbook,Nondestructive Testing Handbook, The NDT Technician and www.asnt.orgare trademarks of The American Society for Nondestructive Testing, Inc.ACCP, ASNT, Research in Nondestructive Evaluation and RNDE are registeredtrademarks of the American Society for Nondestructive Testing, Inc.

®

The NDT TechnicianPO Box 28518 Columbus, Ohio 43228

NONPROFITUS POSTAGE

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The NDT TechnicianA Quarter ly Publ icat ion for the NDT Pract it ioner

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