This past year was an eventful one for AMMTIAC in most

measurable ways, including a change at the top. Last Spring

AMMTIAC welcomed Mr. Mike Morgan to the team as its

new Director.

Mike’s strong background in systems engineering is a timely addition to the organization, as AMMTIAC is in the

process of extending it’s technical reach beyond the basic

enabling technologies of materials, manufacturing, and testing into the more

general domains of design, systems,

manufacturing methods, quality, and

other application-oriented disciplines.

Mike comes most recently from the

aerospace sector where he managed the

testing and development of new materials and processes for thermal management systems in satellite applications. 

He also brings with him an extensive

background in business development,

technology transfer, and program management.

Mike is no stranger to the military,

having spent ten years earlier in his career

as a civilian engineer at the Air Force

Research Laboratory’s Propulsion Directorate in Dayton, Ohio. Among his more

notable accomplishments, he managed

major flight testing programs to evaluate

upgrades to existing and emerging

weapon systems. He also directed and led several multidisciplinary integration teams that were responsible for inserting new technologies into developing military systems.

Moreover, Mike has a genuine appreciation for the needs of

the warfighter, having begun his career in the Navy serving

aboard a nuclear submarine as enlisted personnel. In his six

years as an electrician and a nuclear power plant operator, he

gained an understanding of life in the trenches that few 

could ever hope to acquire vicariously.

“AMMTIAC and its predecessors have a proud history of

service to its traditional user bases, and I am delighted to now

be a part of that,” says Mike, “but the needs of the DoD are

evolving, and so must AMMTIAC’s ability to serve the 

changing mission of the warfighter.” He adds, “Most of

AMMTIAC’s user community know us for this publication,

the AMMTIAC Quarterly – in fact, many people believe that

AMMTIAC is the magazine and are unaware that there is an

entire center of excellence behind it. We are working to

change that perception by becoming

more of a household name. In the past,

we have been successful at providing support to the defense community by being

an information resource through our

technical inquiry service, the Quarterly,

our website, the resources of our 300,000

volume library, and the many databases

and products we offer. However, we can

serve our growing user base even better

by making them aware of all the other

ways we can support organizations and

programs. One of the most important

things I hope to accomplish as Director

is to reach out to the program offices,

product centers, commands, sustainment

centers, and other organizations so we

can directly help them in their missions.”

Mike further points out, “AMMTIAC

is not merely a technology transfer

organization or center of excellence; 

it is also a pre-competed, pre-awarded 

contract vehicle. Being a task order contract vehicle, 

government organizations can utilize the AMMTIAC to get

new work started in a matter of weeks. Rapid response to 

customer needs is one tenet of AMMTIAC’s charter, and we

are committed to serving the community as a one-stop shop

for their needs. I look forward to the challenge of serving the

DoD in this capacity.”

To learn how AMMTIAC can work for you visit:

http://ammtiac.alionscience.com/contractvehicle

• Meet our team

• See examples of work on contract

Meet Our New

Director

Mike Morgan

The AMMTIAC Quarterly is published by the Advanced Materials, Manufacturing, and Testing Information 

Analysis Center (AMMTIAC). AMMTIAC is a DoD-sponsored Information Analysis Center, administratively

managed by the Defense Technical Information Center (DTIC). Policy oversight is provided by the Office of the

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distributed to more than 18,000 materials, manufacturing, and testing professionals around the world.

Inquiries about AMMTIAC capabilities, products, and services may be addressed to: 

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Benjamin D. Craig

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Cynthia Long

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Gina Nash
INTRODUCTION

Corrosion of metallic structures is an industry and governmentwide maintenance problem that has been rapidly spreading due to

the increased amount of infrastructure and military assets that are

aging. However, even in the case of newer systems and components,

corrosion can be a significant problem because of the harsh operational environments encountered. Recognition of the severity and

the resulting economic impact of the corrosion problem by various

industries and government agencies has led to significant effort over

the past 50 years to prevent and control corrosion. Nondestructive

evaluation (NDE) plays an important role in this effort, mostly by

enabling the detection of early signs of corrosion so that corrective

action can be taken before the damage becomes severe.

Hidden Corrosion

Hidden corrosion is a type of electro-chemical material degradation that is not readily or directly detectable visually, or by 

any other surface measurement technique.[1] It can often be

detected and quantified in terms of reduction of wall thickness or

structural discontinuities such as pits, flaws and

voids. When attempting to detect material

degradation due to electro-chemical processes,

the corrosion products (e.g., iron oxides, 

aluminum oxides, etc.) must be identified so

that an appropriate energy source can be selected for detection.

In order to perform an inspection for hidden

corrosion, the detection energy source must be

capable of penetrating the material in which the

corrosion is hidden.[1] If the appropriate

source is selected, then the returned signal will

contain an evaluation of the entire material,

including the physical geometry of the component or system, which may indicate its structural integrity, and any hidden corrosion. Thus,

the inherent technical challenges are to select

the most appropriate interrogation energy

source and to recover the signal that identifies

the existence of corrosion. Recovering the

desired corrosion data is a mathematical inversion problem. Depending on the energy source

used, the characteristics of materials, and the corrosion hidden in

structural systems, an exact solution of the inversion problem may

not be feasible. Therefore, data analysis and information processing, such as the use of neuro-nets, have become key enablers in

developing NDE techniques for hidden corrosion.

The military is considered the primary driver for the development of corrosion detection technology, while the nuclear, chemical, petroleum, and oil and gas pipeline industries are secondary

drivers of this technology. This is due in part to the fact that military systems are typically fielded longer, have higher operational

cycle rates and operate in more corrosive environments than commercial systems.[2] Aging DoD assets have exacerbated the problem

of corrosion and have increased the need for prevention, hidden

corrosion detection, and repair. The corrosion battle extends to

essentially the entire spectrum of DoD systems, including surface

ships, submarines, carrier and land-based aircraft, land vehicles, and

amphibious landing craft. As systems age, corrosion becomes one of

the largest cost drivers in life cycle costs of weapon systems. An

example of this problem is the cables that are used for elevators on

aircraft carriers (Figure 1). These cables are outside the carrier hull

and are exposed to the extremely harsh corrosive environment. Due

to the unavailability of NDE detection technology, these elevator

cables are replaced on a time-based schedule every several years at a

cost of hundreds of thousands of dollars per elevator.

PRIMARY NDE METHODS FOR DETECTING 

HIDDEN CORROSION

Guided Ultrasonic Waves

Guided ultrasonic wave NDE offers the potential for a costeffective methodology for inspection of hidden corrosion in large

and sometimes difficult to access areas, such as

insulated piping. The field of guided waves 

has reached some degree of maturity, but unfortunately the number of practical applications

compared to the number of research papers is

rather small.

Guided waves can be used in three regimes,

depending on inspection distance:

• Short range (<< 1 m)

• Medium range (up to about 5 m)

• Long range (up to around 100 m)

The short range methods include high frequency surface wave scanning with rayleigh waves,

leaky lamb waves, and acoustic microscopy in

which a leaky surface wave is generated by the

lens. The medium range methods typically use

frequencies in the 250 kHz to 1 MHz range

and are applicable to plate, tube and pipe testing. The long range method generally uses long

range frequencies below 100 kHz, and the primary advantage is that it allows a large area to

be tested from a single transducer location

without tedious scanning. Long range testing, which has the greatest potential utility in field-testing, is usually carried out in the

pulse echo mode.

All of the successful applications of long range guided wave testing to date have been on structures with low feature density. This

means that the coherent noise produced by multiple reflections

between different features is modest. However, it would be valuable to be able to test more complex structures, such as aircraft

fuselages, where the spacing between stiffeners is typically less 

than 300 mm. Some initial work has been done on propagation in

this type of complex structure which indicates that subtraction

algorithms may be helpful.[3, 4]

George A. Matzkanin

H. Thomas Yolken

AMMTIAC

Austin, TX

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2 3

Figure 1. An F/A-18C Hornet is Moved

to the Flight Deck on an Aircraft Elevator. (Photo taken by Photographer’s

Mate 3rd Class Todd Frantom and 

Provided Courtesy of the US Navy).
4 The AMMTIAC Quarterly, Volume 2, Number 2

Guided ultrasonic waves have been applied for inspecting pipes by

using an array of transducers around a pipe to focus energy at particular positions on the pipe circumference at chosen axial locations.[5]

Although good results were obtained in a laboratory environment,

this technique was not as successful in actual shipboard tests of piping where pipe elbows, hangers, flanges, valves, welds, etc., add significant complexity. However, this approach still has the potential to

be applied to more complex structures if coherent noise can be controlled and algorithms can be developed to interpret waveforms.

Prior work has shown that guided waves also have some potential

for inspection of multilayer aircraft structures for hidden corrosion

and cracking.[6] Figure 2 (a, b, and c) shows guided wave waveforms

from a three-layer aircraft structure of aluminum-adhesivealuminum. The first signal is from a non-corroded region (Figure

2a), the second is from a corroded region in the bottom aluminum

plate (Figure 2b), and the third is from a corroded region in the top

aluminum plate (Figure 2c).

Non-contact air-coupled transducers can be used to apply guided

waves to the inspection of thinning in aluminum plates.[7] In this

application, a pair of micromachined gas (air)-coupled capacitive

transducers is used for the generation and detection of guided plate

modes. Features in the dispersive behavior of selected guided wave

modes were used for the detection of plate thinning. Mode cutoff

measurements provided a qualitative detection of plate thinning,

while frequency shift measurements were able to provide a quantitative measure of plate thinning. The experimental setup with aircoupled transducers is shown in Figure 3.

Non-contacting electromagnetic acoustic transducers (EMATs)

can also be used to generate and detect shear horizontal (SH)-guide

waves for inspection and mapping of corrosion in pipe walls and

plates.[8] The SH waves have a pure shear-motion parallel to the

surfaces and perpendicular to the plane of incidence. SH-guided

waves have a unique feature in contrast to guided waves with inplane polarization; the lowest order mode has no dispersion and the

dispersion of the higher order modes is much weaker than modes

with polarization in the plane of incidence. As a result, SH-guided

waves could be economically and reliably used to detect and map

corrosion in plates and pipes. Couplant free excitation and the

resultant simplified waveforms add to the versatility and usefulness

of the technique.

A shorter range wave technique that utilizes creeping (or lateral

waves) and head waves in parallel or near-parallel walled metal

structures has been commercialized in the United Kingdom.[9] The

technique utilizes a transducer at the critical angle to generate creeping and head waves, and a second receiving transducer is placed up

to one meter away. The unique way in which the waves propagate

provides complete isonification of the plate or pipe with little attenuation. This allows the probes to be well separated compared to traditional creeping wave inspection. The technique is also applicable

to corrosion in pipes under pipe supports, and the instrumentation

has been field proven.

Ultrasonics

Confidence in ultrasonic inspection to detect and quantify 

corrosion in field applications has often required the disassembly of

systems and testing in water baths. Results of various tests have

shown that the detection of hidden corrosion on various aluminum

alloys of varying thickness was useful above 10% metal loss, but the

technique was not applicable for metal loss below 10%.

To improve the ability for detecting hidden corrosion, there have

been continued efforts to apply the dripless bubbler ultrasonic scanner, which is an ultrasonic technique that does not require a water

bath and disassembly.[10] This technique was selected as a primary

candidate by the Air Force Logistics Center in Oklahoma City (OCALC) for the detection and quantification of intergranular corrosion

prior to the onset of exfoliation around wing skin fasteners. This is a

major inspection problem for aging aircraft. Figure 4 shows the

results of tests for corrosion detection around wing-skin fasteners.

In a similar NDE study, a novel ultrasonic pulse echo technique

was developed to detect intergranular corrosion around fastener

holes in aluminum wing skins before the exfoliation stage.[11] In

this case, a focused transducer with a special fixture was used to

overcome the typical problems: not enough couplant, transducer

not perpendicular to the part, and varying transducer pressure. In

general, there was good agreement between the ultrasonic results

and the results from the mechanical rework of the wing skin and

dissection of the fastener hole.

Ultrasonics can also be applied without a water bath by using laserultrasonics.[12] Laser ultrasonics have been applied for the inspection

of painted metal skin, aircraft lap joints. When lap joint corrosion

reaches a specific level, normally 10% of the nominal skin thickness,

the section of the lap joint must be replaced. Visual inspection of the

pillowing of the surface has been used to detect this type of corrosion,

but it cannot supply quantitative information. By using spectral

Figure 2. Waveforms for a Three-Layer Structure, AluminumAdhesive-Aluminum, (a) Non-Corroded Region, (b) Corroded Region

at the Bottom, (c) Corroded Region at the Top. (Reprinted with 

permission from[6] © 2000 American Institute of Physics.)

Figure 3. Experimental Setup for Gas (Air) – Coupled Ultrasonic 

Guided Wave Detection of Thinning Defects in Aluminum Plates.[7]

Simulated Hidden Co rision

Test Plate

Transmitter Receiver

Monitor Signals

Control/Acquisition

Charge Amplifier

AC/DC

Decoupler

Osci loscope

200V Bias

Computer

Receiving

Module

RITEC

RAM-10000

Gated

Amplifier

00

90

80

70

60

50

40

30

20

10

0 dy Current A dy Current B ltrasonic Testing Dripless Bubbler (Sierr Matrix)

ripless Bubbler

ISU)

Therma A Therma (Wayne

tat niv

Hit % – Within Shadow Hit % Beyon hadow False Call Rat e

Figure 4. Corrosion Detection around Wing-Skin Fasteners – 

Chemically Induced Intergranular Corrosion Trial Results.[10]*

150

0

-150

0 50 100 150

time(μs)

0 50 100 150

time(μs)

0 50 100 150 time(μs)

Amplitude

150

0

-150

Amplitude

150

0

-150

(a) (b)

(c)

Amplitude
analysis of the laser-ultrasonic waveforms,

the residual metal skin thickness of the top

skin of the lap joint could be determined.

Results from standard samples with flatbottom holes showed that the technique

could detect metal loss below 1% of the

nominal thickness of the metal skin. Comparison of the laser-ultrasonic measurements to X-ray images showed that the

laser-ultrasonics has the same accuracy as

the X-ray imaging (metal loss below 1%).

However, laser-ultrasonics as compared to

X-ray imaging does not require disassembly

of the structure, and the inspection could

be carried out during routine maintenance.

Other ultrasonic approaches for detecting hidden corrosion involve ultrasonic

imaging using dry-coupled probes.[13] In

addition, a commercial instrument that

essentially operates as an “ultrasonic camcorder” can produce C-scan images from

ultrasound signals, which are introduced

into the sample with a large, unfocused

commercial transducer.[14] The implementation can be either in transmission or

reflection. A water squirter or ultrasonic

couplant on the surface is required for the

application of this technique.

By combining obliquely backscattered

ultrasonic signals with the sensor array

real-time charge-coupled imaging system

used in the ultrasonic camcorder, a rapid

technique for detecting corrosion in aircraft skins without the need for paint

removal has been developed.[15] The

system can produce 30 frames a second and the unit can be programmed to examine time-of-flight bounds and thus produce 3D

images of material slices. Figure 5 shows a schematic of the technique and Figure 6 shows a pulse-echo image of a corroded area in

an aluminum plate. The combination of obliquely backscattered

ultrasonic signals and the charged-coupled ultrasonic imager produces a viable aircraft corrosion inspection technique.

Eddy Current

Eddy current NDE is a prime method for detecting hidden corrosion in electrically conducting materials. The method is based on

generating a localized alternating current field in the sample using a

probe coil. The same probe coil or another detector then measures

the material’s response to the induced eddy currents. Defects cause

a perturbation in the eddy currents, and this can be detected by a

change in impedance or phase variation in the detecting circuit. In

the past, eddy current NDE was limited in detecting hidden corrosion to very shallow depths by the lack of penetrating capability of

the eddy currents. However, over the last several years there have

been several notable advances in eddy current NDE stemming from

research to detect hidden corrosion and other types of defects.

When combined with magnetoresistive sensors, eddy currents can

be used to detect corrosion in second and third layers in aircraft lap

joints.[16] High performance magnetoresistive sensors are much

more sensitive than standard pick up coils used in conventional eddy

current NDE, and they operate at much lower frequencies. Their 

low frequency range and linear response to frequency allows for

much greater depth of inspection than with conventional eddy 

current NDE that operate at higher frequencies.

Pulsed eddy current NDE technology

has also made recent advances.[17] Its

robustness to variations in geometry, paint

thickness, rivet heads, surface warping,

and sensor liftoff are allowing this technology to become a major method for detection of hidden corrosion. Conventional

eddy current instruments measure the

impedance and reactance of the detection

coil, while the pulsed eddy current instrument measures the transient voltage signal

with a frequency spectral content from

direct current to 100 KHz or higher. This

broadband characteristic provides the ability to conduct digital signal analysis and to

extract subtle differences in waveforms

associated with small geometry variations.

Hence, it provides the ability to quantify a

large number of parameters. For example,

material loss at or near the surface will

have more of an effect on the early-time

portion of the total transient interval than

on the late-time portion. The opposite

will be true for very deep defects.

Remote field eddy current is another

variation of conventional eddy current

that has found widespread use in detecting

hidden corrosion. Its capabilities have

recently been expanded and automated.[18] The remote field eddy current

technique is based on the measurement of

the voltage induced in a pickup coil by

flux which has passed twice through the

test piece as shown in Figure 7. Measurement of the phase change caused by a discontinuity has a linear relationship with changes in thickness of the

pipe wall. Remote field eddy current is not sensitive to liftoff, but an

ultra sensitive eddy current system is required to handle the very low

amplitude signals obtained from remote field eddy current probes.

Magneto-optical imaging of eddy currents is another innovative

advance in eddy currents applied to detection of hidden corrosion.[20] Magneto-optical imaging of the eddy currents generates

real-time images of large surface areas to quickly detect subsurface

corrosion and cracking. Although eddy current techniques do not

have as much sensitivity and spatial resolution as ultrasonic NDE

techniques, the ability to detect corrosion in multiple layer structures and at greater depths are advantageous.

Thermography

Thermography provides a fast, non-contact technique for detection

of subsurface corrosion. Thermography is based on using the thermal differences between a material and material defects to image

discontinuities such as corrosion. It has demonstrated ability to

detect corrosion under paint without paint removal. In addition,

advances in commercial instrumentation and algorithms, particularly for thermal wave techniques[21], have substantially enhanced

field applications. Moving linear heat sources have also enhanced

thermographic capability.

Thermal wave systems operate by sending a pulse of heat from the

surface into the material, where it undergoes thermal reflection at

either the rear surface or at thermal impedance changes (e.g. corrosion). The effect of these thermal reflections is that it modifies the

local cooling rate at the surface. The cooling rate, in turn, is monitored through its effect on the IR radiation from the surface. The IR

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2 5

Figure 5. A Schematic View of the Wavefield in a

Painted 2-Layer Structure.[15]

Figure 7. Two Energy Coupling Paths in a Remote

Field Eddy Current Probe for Pipe Testing.[19]

Figure 6. A Pulse-Echo Image of Corroded Area in

an Aluminum Plate Visualized by the Current Sensor

Array Real Time Imaging (SARTI) System. The Depth

Data Represent the Information at the Crosshair

Cursor Location.[15] (Reprinted with permission

from SPIE)

Specular Reflection

Transducer

Corrosion

Paint

Skin

Primer

Bond

Substructure (Stiffener, T-Cap, Stringer, etc.)

Incident Beam Non-Specular Reflection

Direct Energy Coupling Path

Indirect Energy Coupling Path

Indirect Energy Coupling Path

Excitational

Coil

Pick-up

Coil
radiation is detected by an IR camera and processed as a sequence of

images by the control computer.

Figure 8 shows a thermal wave image of two KC-135 wing fastener regions, one with corrosion and one without. The authors concluded that thermal wave imaging is an excellent tool for inspecting

aircraft for corrosion and can rapidly (in the matter of a few seconds) make quantitative measurement of less than 1.0% material

loss. Thermal waves can also be used to detect corrosion under paint

on airplane skin in the presence of irregular paint thickness. This

work was validated in a blind test on a DC-9 belly skin.[22]

A number of other heat source techniques applied to thermography to detect corrosion have been demonstrated. Hot air guns as

heat sources for thermography (named fan thermography) have

been shown to detect corrosion in aircraft structures.[23] A quartz

line-shaped heat source (3000 watt quartz lamp with an elliptical

reflector) moving at speeds of 2.5 to 12.2 cm/sec has also been

demonstrated to provide a back surface profile.[24] Using neural

nets for mapping the data, metal thickness could be determined to

within 5% of the actual thickness.

Thermographic NDE techniques are not currently in widespread

use. However, the rapid inspection times for broad areas of coverage, availability of instrumentation, and ease of use should quickly

lead to a wider use in the field.

CONCLUSIONS

In the past, NDE of hidden corrosion was a difficult challenge.

However, in the last decade substantial advances in NDE methodology and software have made the challenge much more tractable.

For example, eddy current can now detect corrosion in second and

third layers of aircraft lap joints. Pulsed eddy current NDE, low frequency eddy current NDE with magnetoresisitive sensors, remote

field eddy current NDE at low frequencies using Hall probes, and

magneto-optical imaging of eddy currents have greatly increased the

tools available to detect hidden corrosion.

Thermography has also undergone great advances in the past

decade, and it is now widely used to detect corrosion under paint.

Advances in commercial instrumentation and software, particularly

for thermal wave imaging, have enhanced field applications. Moving linear heat sources and algorithms have also broadened the field

applications of conventional thermography. These advances in thermography, coupled with wide field of view and rapid inspection

times, will result in the continued expansion of field applications.

In the past, ultrasonic techniques were mainly limited to inspecting

disassembled systems in a water bath. However, advances in ultrasonic

methods (e.g. the dripless bubbler) have now expanded the applications for detecting corrosion. In addition, laser ultrasonics should continue to find niche field applications as it has over the past decade, but

the rate of market penetration will most likely remain very modest due

to the complexity of the technique. Guided wave ultrasonics has been

shown in a number of research settings to be capable of inspecting large

areas for hidden corrosion in difficult to access areas. However, transition of this capability, with its complex analysis, to commercial applications is expected to continue to proceed very slowly.

Other NDE techniques, such as X-ray radiology and optical techniques, should continue to find niche field applications. In summary, the future looks bright for existing techniques and for improving

field NDE capability to detect hidden corrosion.

NOTE AND REFERENCES

* Shadow refers to the shadow of the fastener countersink.

[1] J.C.I. Chang, “Aging Aircraft Science and Technology Issues and Challenges 

and USAF Aging Aircraft Program”, Structural Integrity in Aging Aircraft, ASME:

AD-Vol. 47, 1995.

[2] “Corrosion Detection Technologies”, BDM Federal Inc., March 1998.

[3] R.P. Dalton, P. Cawley and M.J.S. Lowe, “Propagation of Acoustic Emission 

Signals in Metallic Fuselage Structure,” IEEE Proceedings: Science, Measurement and

Technology, Vol. 148, 2001a, pp. 169-177.

[4] R.P. Dalton, P. Cawley and M.J.S. Lowe, “The Potential of Guided Waves for

Monitoring Large Areas of Metallic Aircraft Fuselage Structure,” Journal of NDE,

Vol. 20, 2001b, pp. 29-46.

[5] M.J. Quarry and J.L. Rose; “Multimode Guided Wave Inspection of Piping

Using Comb Transducers,” Materials Evaluation, Vol. 57, No. 10, October 1999, pp.

1089-1090.

[6] L.E. Soley and J.L. Rose, “Ultrasonic Guided Waves for the Detection of Defects

and Corrosion in Multi-Layer Structures,” Review of Progress in Quantitative 

Nondestructive Evaluation, Vol. 19B, 2000, pp. 1801-1808.

[7] D. Tuzzeo and F. Lanza di Scalea, “Noncontact Air-Coupled Guided Wave 

Ultrasonics for Detection of Thinning Defects in Aluminum Plates,” Research in

Nondestructive Evaluation, Vol. 13, No. 2, 2001, pp. 61-77.

[8] H.J. Salzburger, “Long Range Detection of Corrosion by Guided Shear Horizontal (SH-) Waves,” The 7th European Conference on Non-Destructive Testing, Copenhagen, May 1998, pp. 751-757.

[9] F. Ravenscroft and C. Bull, “Corrosion Detection Using CHIME,” Insight,

Vol. 42, No. 2, February 2000, pp. 80-83.

[10] D.J. Barnard and D.K. Hsu, “Detection and Quantification of Intergranular Corrosion Around Wing Skin Fasteners Using the Dripless Bubbler Ultrasonic Scanner,” Review

of Progress in Quantitative Nondestructive Evaluation, Vol. 18B, 1999, pp. 1821-1828.

[11] P.S. Rutherford, “NDI Method to Locate Intergranular Corrosion Around 

Fastener Holes in Aluminum Wing Skins,” SPIE, Vol. 3397, 1998, pp. 57-66.

[12] M. Choquet, D. Levesque, M. Massabki, C. Neron, N.C. Bellinger, D. Forsyth,

C.E. Chapman, R. Gould, J.P. Komorowski and J.P. Monchain, “Laser-Ultrasonic

Detection of Hidden Corrosion in Aircraft Lap Joints: Results from Corroded 

Samples,” Review of Progress in Quantitative Nondestructive Evaluation, Vol. 20B,

2001, pp. 300-307.

[13] I.N. Komsky, “Ultrasonic Imaging of Hidden Defects Using Dry-coupled 

Ultrasonic Probes,” Health Monitoring and Smart Nondestructive Evaluation of 

Structural and Biological Systems V, edited by Tribikram Kundu, Proc. of SPIE, 

Vol. 61770M, 2006.

[14] M. Lasser, B. Lasser, J. Kula and G. Rohrer, “Developments in Real-Time 2D

Ultrasound Inspection for Aging Aircraft,” SPIE Conference on Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware III, Vol. 3586, 1999, pp. 78-84.

[15] Y. Bar-Cohen, A.K. Mal and M. Lasser, “NDE of Hidden Flaws in Aging 

Aircraft Structures Using Obliquely Backscattered Ultrasonic Signals (OBUS),” The

SPIE Conference on Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware III, Vol. 3586, 1999, pp. 347-353.

[16] R. Rempt, “Scanning with Magnetoresistive Sensors for Subsurface Corrosion,”

Review of Quantitative Nondestructive Evaluation, Vol. 21B, 2002, pp. 1771-1778.

[17] S. Giguere, B.A. Lepine and J.M.S. Dubois, “Pulsed Eddy Current Technology:

Characterizing Material Loss with Gap and Lift-off Variations,” Research in 

Nondestructive Evaluation, Vol. 13, No.3, 2001, pp. 119-129.

[18] M.S. Safizadeh, Z. Liu, C. Mandache, D.S. Forsyth and A. Fahr, “Automated

Pulsed Eddy Current Method for Detection and Classification of Hidden 

Corrosion,” Proc. Vth International Workshop, Advances in Signal Processing for 

Non Destructive Evaluation of Materials, Quebec City (Canada), 2-4 Aug. 2005, 

X. Maldague ed., E. du Cao, 2006, pp. 75-84.

[19] Y.S. Sun, T. Ouang and S. Upda, “Remote Field Eddy Current Testing: One 

of the Potential Solutions for Detecting Deeply Embedded Discontinuities in Thick

and Multilayer Metallic Structures,” Materials Evaluation, Vol. 59, No. 5, May 2001,

pp. 632-637.

[20] D.K. Thome, “Development of an Improved Magneto-Optic/Eddy-Current

Imager,” Published by The National Technical Information Service (NTIS), Springfield,

Virginia, April 1998.

[21] L.D. Favro, R.L. Thomasand and X. Han, “State-of-the-Art of Thermal Wave 

Imaging for NDE of Aging Aircraft,” Nondestructive Evaluation of Aging Aircraft, 

Airports, and Aerospace Hardware III, SPIE Vol. 3586, March 1999, pp. 94-97.

[22] X. Han, L.D. Favro, L. Li, Z, Ouyang, G. Sun, R.L. Thomas and D.M. 

Ahsbaugh, “Quantitative Thermal Wave Corrosion Measurements on a DC-9 Belly

Skin in the Presence of Irregular Paint Thickness Variations,” Review of Progress in

Quantitative Nondestructive Evaluation, Vol. 20A, 2001, pp. 483-486.

[23] N. Meyendorf, J. Hoffman and E. Shell, “Early Detection of Corrosion in 

Aircraft Structures,” Review of Quantitative Nondestructive Evaluation, Vol. 21B,

2002, pp. 1792-1797.

[24] W.P. Winfree and K.E. Cramer, “Reconstruction of Back Surface Profiles from

Scanned Thermal Line Source Data Using Neural Networks,” Review of Progress in

Quantitative Nondestructive Evaluation, Vol. 19A, 2000, pp. 691-698.

6 The AMMTIAC Quarterly, Volume 2, Number 2

Figure 8. Thermal Wave Image

of Two KC-135 Wing Fastener

Regions, One Revealing Subsurface Intergranular Corrosion,

Extending from the Lower Right

Edge of the Fastener (Left); 

the Other with No Corrosion

(Right).[21] (Reprinted with 

permission from SPIE.)
INTRODUCTION

After visual and optical testing (VT), the next method of nondestructive testing (NDT) most commonly employed in industry is

radiographic testing. Also simply referred to as radiography, it is

perhaps the most versatile of the nondestructive testing methods.[1] The basic radiographic process in use today is in large part

still the same as it was when it was introduced in the late 1800s.

Radiography uses radiation energy to penetrate solid objects in

order to assess variations in thickness or density. The second part

of the process involves capturing a shadow image of the component being inspected on film using procedures similar to those that

technicians used when the technology was first

developed. Identifying density differences on an

X-ray, which indicate flaws or cracks, is still the

foundation of radiographic analysis.

PHYSICAL PRINCIPLES

Radiography basically involves the projection

and penetration of radiation energy through the

sample being inspected. The radiation energy is

absorbed uniformly by the material or component being inspected except where variations in

thickness or density occur. The energy not

absorbed is passed through to a sensing medium

that captures an image of the radiation pattern.

The uniform absorption and any deviations in

uniformity are subsequently captured on the

sensing material and indicate the potential presence of a discontinuity.

Image Capturing Media

In simple terms, a radiograph is a photographic record produced by

the passage of X-rays or gamma rays through an object onto a film

or other recording medium (see Figure 1). The developing, fixing

and washing of the film after exposure can be performed manually or by automated processing equipment. The development

process begins after the film is exposed to the radiation and an

invisible change called a latent image develops on the film emulsion. These exposed areas become dark when the film is placed in

a developing solution. The degree of darkening that occurs during

this process depends on the amount of exposure that occurred. The

next step is to place the film into a special bath and rinse it to stop

the development process. Lastly, the film is put into a fixing bath

and then washed to remove the fixer solution. At this point the

film is fully developed, the process is complete and the radiograph

is ready to be handled and analyzed.[1]

As the digital world has evolved, a quicker and much more 

efficient alternative to the meticulous film development process

has also emerged to benefit the radiography NDT community.

Computed radiography, which is described in

the related article entitled “Computed Radiography in the Pacific Northwest: Benefits, Drawbacks and Requirements”, makes use of an

alternative image capturing media and development process.

Electromagnetic Radiation

Two types of electromagnetic radiation are used

to perform radiographic inspection: X-rays and

gamma rays (see Figure 2). The primary distinguishing characteristic between these two types

of radiation is the different wavelengths of the

electromagnetic energy. Compared to other

types of radiation both X-rays and gamma rays

have relatively short wavelengths which allows

them to penetrate opaque materials. This 

inherent capability is what enables their use 

for nondestructive testing, as they can reveal

flaws embedded in visually non-transparent materials. The advent

of radiography came quickly after the discovery of X-rays because

of the penetration properties of this electromagnetic energy.[3]

Types of Discontinuities

A number of different types of discontinuities can be detected 

with radiographic NDT. Table 1 lists the suitability of traditional

radiographic NDT methods for identifying various types of 

discontinuities in several applications.

Brett J. Ingold

AMMTIAC

Rome, NY techsolutions solutions 5

A Brief Introduction to Precious Metals

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2

Selecting a Nondestructive Testing Method, Part IV: Radiography

7

This edition of TechSolutions is the fourth installment in a series dedicated to the subject of nondestructive testing. 

TechSolutions 1, published in Vol. 1, No. 2 of the AMMTIAC Quarterly, introduced the concept of nondestructive 

testing and provided brief descriptions of the various techniques currently available. TechSolutions 2 and 3, published 

in subsequent issues of the AMMTIAC Quarterly, focused on visual inspection and eddy current testing. The current 

article continues the series and provides a general and informative overview of the radiography nondestructive testing

method. In addition, this article will highlight some of the physical principles, inspection requirements, and implementation considerations involved in an effective radiographic inspection process.1 Once the series on nondestructive testing 

methods is complete, we will combine all of the articles into a valuable desk reference on nondestructive testing and place

it on our website. – Editor

Figure 1. Diagram of Typical 

Radiography Test Setup.[2]

Radiation Source

Beam

Flaw

Image of Flaw

Test Piece

(Object)

Medium for

Converting

the Radiation
techsolutions 5

8 The AMMTIAC Quarterly, Volume 2, Number 2

INSPECTION REQUIREMENTS

Several critical elements are required to successfully analyze the

results of radiographic testing. Because of differences in density

and variations in composition, different test pieces can absorb

varying amounts of radiation and therefore present a range of

results. Technicians and radiologists each require several years of

training to properly set up and administer tests and inspections

and to learn how to evaluate

and interpret the results.

Also, as the industry continues to develop, some forecasts suggest that in the

future X-rays will be read

almost exclusively by computers. This specific advancement, however, would not

necessarily eliminate the

high costs associated with

set up tasks, which consumes a significant portion

of the total radiographic

inspection time.

Safety

Safety is an important issue

to consider when evaluating

a new process for implementation, especially one such as radiography that requires the

use of radiation. Several governing bodies, including local and

state governments, work together to closely monitor anyone who

works with radiography equipment to ensure that the highest

levels of safety are consistently met.

The licensing and certification process for individuals working

with radiography equipment, which emits radiation, requires

both a written examination and an assessment of specific skills

while using the equipment. The primary governing body that

administers the written examination is the American Society of

Nondestructive Testing (ASNT). The practical skills evaluation

can be conducted by a variety of institutions that have approval

from ASNT. With successful completion of these safety requirements, the applicant will be certified as an Industrial Radiography Radiation Safety Personnel (IRRSP) member. ASNT

offers more detailed information on the entire certification

process, including a more specific list of requirements.[4]

PRACTICAL CONSIDERATIONS

There are several factors to take into account when considering

the implementation of a radiographic inspection program. Some

of the most important factors include: cost, density, facility size

and logistics. Compared to other nondestructive testing methods, radiography is expensive. Relatively large costs can be

reduced considerably when portable X-ray or gamma-ray sources

are used in film radiography because this setup only requires

space for film processing and analysis. With real-time radiography, operating costs are usually much lower, because setup times

are shorter and there are no extra costs for processing or interpretation of film.

Advantages and Disadvantages

Like all other NDT methods, there are several advantages 

and disadvantages that factor into deciding where and when

radiography is typically applied. In relation to other commonly used NDT methods, the well-proven method of radiography

has three main advantages: the ability to detect internal 

flaws, the ability to detect significant variations in composition, and the ability to establish a

permanent record

of raw inspection

data. Radiography also presents

test results pictorially which can be

much more readily

interpreted than

numerical data.

In addition, realtime radiography

offers the ability

to rotate a test

object during inspection, which improves detection of both

internal and external flaws due to the ability to find the optimum orientation.

On the negative side, orientation of the sample to be

inspected is a key to successful radiographic inspection and

therefore can pose difficulties if the proper orientation is not

found. For example, radiography is not as effective at detecting

flaws that are oriented in a planar direction with respect to the

radiation source. Thick inspection samples are also problematFigure 2. Electromagnetic

Spectrum Showing X-ray and

Gamma Ray Regions.[1]

X-Rays

Gamma Rays Ultraviolet Infrared

Visible

10-2 100 102 104 106

A review of radiographs from an F-15 Eagle to

check for foreign object debris and cracks 

in the aircraft's structure. (Photo taken by

Staff Sgt. Shelley Gill and provided courtesy

of US Air Force)

A non-destructive inspection technician

(NDI) evaluates an X-ray image of 

an A-10 Thunderbolt II aircraft nose

landing gear door for cracks. NDI 

technicians are tasked with finding 

and confirming discontinuities on the

airframe and its parts using methods

such as Eddy Current, Fluorescent 

Penetrant, Magnetic Particles, Ultra

Sound and X-ray. (Photo taken by 

Airman 1st Class Alesia Goosic and 

provided courtesy of US Air Force)

Wavelengths in angstrom units (A), where 1 A = 10-8 cm = 3.937x10-9 in.
http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2 9

AMMTIAC A DVANCED M ATERIALS , M ANUFACTURING AND T ESTING

ic for radiography methods. Radiation sources can pose health

and safety risks which is another disadvantage of the method.

The tedious film processing requirement of radiography and

associated special facility requirements have traditionally been

a distinct disadvantage; however, with the advent of digital

imaging and computed radiography many of these limitations

have been overcome.

CURRENT TRENDS AND FUTURE ADVANCEMENTS

In order to meet the constantly changing demands of industry,

various new sources of radiation, such as neutron generators

and radioactive isotopes, are continually being developed.

Other ongoing advances also include improved X-ray films and

automatic film processors, as well as improved or specialized

radiographic techniques.

Table 1. Suitability of Traditional Radiographic NDT Methods for Various Types of Discontinuities in Light and Heavy Metals.[3]

Suitability for Light Metals Suitability for Heavy Metals

Inspection Application Film Real-Time Film Film Real-Time Film 

with X-rays Radiography with γ-rays with X-rays Radiography with γ-rays General

Surface cracks* 3 3 3 3 3 3

Internal cracks 3 3 3 3 3 3

Voids 4 4 4 4 4 4

Thickness 3 4 3 3 4 3

Metallurgical variations 3 3 3 3 3 3

Sheet and plate

Thickness 4 4 4 4 4 4

Laminations 1 1 1 1 1 1

Voids 4 4 4 4 4 4

Bars and tubes

Seams 2 2 2 2 2 2

Pipe 4 4 4 4 4 3

Cupping 4 4 4 4 4 3

Inclusions 3 3 3 3 3 3

Castings

Cold shuts 4 4 4 4 4 4

Surface cracks 3 3 3 3 3 3

Internal shrinkage 4 4 4 4 4 4

Voids, pores 4 4 4 4 4 4

Core shift 4 4 4 4 4 4

Forgings

Laps 2 2 2 2 2 1

Inclusions 3 3 3 3 3 1

Internal bursts 4 4 4 3 3 4

Internal flakes 2 2 1 2 2 1

Cracks and tears 3 3 3 3 3 3

Welds

Shrinkage cracks 4 4 4 4 4 4

Slag inclusions 4 4 4 4 4 4

Incomplete fusion 4 4 4 4 4 4

Pores 4 4 4 4 4 4

Incomplete penetration 4 4 4 4 4 4

Processing

Heat-treat cracks 1 1 1 2 1 1

Grinding cracks 1 1 1 1 1 1

Service

Fatigue and heat cracks 3 3 2 2 2 2

Stress corrosion 3 323 32

Blistering 2 2 2 2 2 2

Thinning 3 3 3 3 3 3

Corrosion pits 3 3 2 4 4 2

4 - Good, 3 - Average, 2 - Fair, 1 - Poor
10 The AMMTIAC Quarterly, Volume 2, Number 2

techsolutions 5

However, with today’s technology it is now possible to generate images of higher quality and sensitivity. The higher quality of

radiographic images is primarily due to improved films that have

a wider variety of available grain sizes. Also, with the addition of

computers and other advanced electronic systems to the process,

the advent of digital radiography has proved to be a large

advancement within the industry.

With the use of digital radiography, a radiographic image captured today can theoretically be preserved forever and sent anywhere in the world almost instantly. In earlier cases, there had to

be concerns with deterioration of the image that no longer have

to be taken into account today. This ability to continually

improve the process has led to growth of radiography into

numerous industries. Radiography has seen expanded use in

industry to inspect welds and castings, airbags and canned foods,

to name a few. The area of metallurgical material identification

and security systems has also employed radiography NDT at airports and other facilities with security needs.[1, 5]

CONCLUSION

Radiography is a mature NDT method that can be used to effectively detect several types of discontinuities embedded within a

variety of types of materials and components. Since the method

has been in use for many years, the drawbacks and shortcomings

are well-known. Some of these limitations have been overcome

with the rapid advancement of digital technology. Radiography

has continued to evolve by embracing certain aspects of the 

digital era, and consequently it has become a more flexible and

viable method for nondestructive evaluation.

REFERENCES

[1] “Radiography in Modern Industry,” 4th Edition, R.A. Quinn 

and C.C. Sigl, Editors, Eastman Kodak Company, 1980, http://

www.kodak.com/eknec/documents/87/0900688a802b3c87/Radiogra

phy-in-Modern-Industry.pdf

[2] “Radiography Testing,” Engineer’s Handbook, http://www.engi

neershandbook.com/MfgMethods/ndtrt.htm

[3] “Radiographic Inspection,” ASM Metals Handbook, Ninth 

Edition, Vol. 17, Nondestructive Evaluation and Quality Control,

ASM International Metals Park, OH, pp. 296-357.

[4] “Industrial Radiography Radiation Safety Personnel,” ASNT 

Practice No. ASNT-CP-IRRSP-1A, 2001 Edition, American Society 

for Nondestructive Testing, http://www.asnt.org/certification/irrsp/

cp-irrsp-1a.pdf.

[5] “Introduction to Radiographic Testing,” NDT Resource Center,

http://www.ndted.org/EducationResources/CommunityCollege/Radio

graphy/Introduction/presentstate.htm.

Table 1. Radiography Summary

Discontinuity types • Voids

(e.g. what types the method can detect) • Inclusions

• Cracks

• Non-uniformity of material

• Density changes

• Weld defects

Size of discontinuities • Discontinuities that exhibit 1% or more absorption difference relative to surrounding region

• Advanced systems can detect flaws as small as 0.001 inches

Limitations • Orientation of inspection sample

• Not suitable for surface defects

• As thickness increases, detection effectiveness decreases

• Large amounts of equipment required for non-portable setup

• Film limitations

• Manual image interpretation

Advantages • Can be used to detect defects in a variety of materials

• Can detect internal defects

• Permanent inspection record

• Objects radiographed range in size from micro-miniature electronic parts to 

large missile components

• Makes it easier to maintain a defect-free and uniform product line

Inspector training (level and/or availability) • Variety of programs available nationally to study the science of radiology

Inspector certification required • Radiation safety training is critically important

• ASNT offers certification for radiography safety

Equipment • Portable or fixed setups depending on industry/company requirements and desired function

• Traditional radiography requires film development facilities and equipment

Relative cost of inspection • Depends on setup, but cost can be greatly reduced with the use of portable equipment 

that requires less space
http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2

INTRODUCTION

Like many other Navy regions, Commander Navy Region

Northwest (CNRNW) was faced with replacing its aging

chemical and film-based radiographic imaging systems that

were being used for nondestructive testing (NDT). At

CNRNW, several activities acquired computed radiography

(CR) systems via the Pollution Prevention Equipment Program

(PPEP) to replace the conventional NDT systems. The new

CR systems have been installed and used, and the intent of this

article is to report on the benefits, requirements, concerns, and problems associated

with implementing this new technology for

CNRNW.

THE BASICS OF COMPUTED 

RADIOGRAPHY SYSTEMS

Computed radiography is a type of digital

radiography. Similar to conventional radiography, CR systems create an X-ray image of

the part under inspection. Unlike a filmbased system, however, the end result is a digital image. (The sidebar contains a summary

of three radiography inspection technologies). CR systems have four main elements,

including a phosphor image plate (IP), an IP

reader (see Figure 1), a central processing station with special software (see Figure 2), and

a high-resolution monochrome X-ray monitor. The IP surface is coated with storage

phosphors that capture and store the incident

radiation energy from the X-ray source to create a latent image

on the plate. After the IP is exposed to the radiation energy it is

processed in the IP reader where a low energy laser is used to

release visible light from the stored energy. The visible light is

then converted into an electrical signal which can be converted

into digital data. The storage image phosphors will retain the

latent image for periods ranging from several hours to days,

depending on screen phosphor material and exposure duration;

however, the plates can be reused numerous times once the latent

image is cleared. Similar to conventional X-ray film, phosphor

plates are stored in cassette format.

Why the Move Away from Film?

Several factors are influencing the move away from film-based

X-ray techniques toward CR systems. CR systems eliminate

costly chemicals and resulting hazardous waste, provide an

adaptable image medium, reduce other consumables that filmbased systems require, protect worker health and safety,

improve productivity by reducing work turn-around time and

make test results readily available to off-site experts. Each of

these benefits is described in the following sections.

Elimination of Chemicals and Hazardous Materials

With CR systems, images are generated on a medium that

does not require the chemical bath processing used for 

producing traditional film. Moreover, traditional film

chemicals must be used within a limited timeframe, which

requires processing labs to maintain a fresh stock of chemicals. The cost of procuring and maintaining these supplies

is expensive, and the film developing chemicals must be

disposed of as hazardous waste. Therefore, by utilizing 

the CR systems, chemicals and hazardous materials are

eliminated.

Greg A. Levcun

Naval Facilities Engineering Command Northwest

Christopher S. Mahendra

Naval Air Systems Command

11

Figure 1. An NDI Inspector Works with the

IP and Reader.

Figure 2. An Inspector Looks at Two Views

of a Defect.
12 The AMMTIAC Quarterly, Volume 2, Number 2

Adaptable Image Medium

Computed radiography’s IP is typically only 0.025 inch thick

and can easily be cut with scissors or a knife. Image plates can

be shaped to meet specific imaging needs, although the cut portion must be refit onto a standard size IP for reading the image.

Reduction of Consumables and Lab Equipment

The imaging plates can be reused between 200 and 5,000

times, unlike traditional X-ray film, which can only be used

once. Other consumables eliminated by using CR include

envelopes, marking pencils, cleaning materials, gloves, and

shields. Computed radiography systems also eliminate several

pieces of support equipment in addition to the developing

tanks and processors, including water chillers, safe lights, silver

recovery units, light-tight doors or light traps, film viewers,

and densitometers used for checking film density and proper

exposure settings.

Worker Health and Safety

Compared to conventional radiography techniques, CR test

operators are not exposed to film processing chemicals and are

subjected to significantly less radiation. The ALARA concept

(“As Low As Reasonably Achievable”) is used within the Navy

to control radiation exposure. In order to comply with

ALARA, an operator must use some combination of time,

distance, and shielding to minimize exposure. In the case of

CR, both the amount of radiation and the length of exposure

are significantly reduced compared to film, which makes the

operator’s task safer and faster.

Productivity Improvements

The opportunities for productivity improvements are substantial as a result of using CR. First, the reduced radiation dose per

exposure and shorter exposure times per shot allow CR inspections to occur within a smaller shielded area. This contributes

to quicker inspection site set-up and allows other work efforts

to continue nearby. The decreased exposure times also make the

inspection process shorter, reducing personnel time. Second,

image processing times are down from a minimum of 12 minutes for film to one minute for CR. This enables the system

operator to determine quickly if shots are acceptable or need to

be retaken. Third, with CR an operator can manipulate the

presentation density and inspect a wider range of material

thicknesses with a single exposure on a single imaging plate as

opposed to taking multiple film shots that use either different

exposure times or different film speeds. Finally, CR systems

allow users to transmit, evaluate, and store images electronically (see Figure 3). The digital format makes internet transmission possible and reduces the storage space required compared

to that required for storing traditional film.

An additional consideration is the future availability of film.

As conventional film becomes less prevalent in the consumer

world, it is projected that industrial access to conventional film

will become more limited.

Limitations of Computed Radiography

While CR offers several operational advantages over conventional film processing, it also has its limitations. As with any

new technology, it has both a learning curve and an acceptance

Radiography is a nondestructive testing (NDT) technique used to volumetrically examine interior components to ensure the part is free of detrimental defects. X-rays or gamma rays are projected through the

component onto an imaging medium. Traditionally, the imaging medium was film. NDT applications

are now moving toward digital imaging, much like individuals have moved to digital cameras and 

dentists and doctors to digital X-rays. Some of the differences among technologies are noted below:

Film-based radiography – X-ray sensitive film is exposed to radiation source. After exposure, the film

holds a latent image (i.e., not visible) until it is developed in a chemical bath to reveal the image of the

component.

Computed radiography (CR) – In place of film, a plate with photo-sensitive storage phosphors is

exposed. When the phosphors are stimulated by radiation, they hold a latent image, much like film.

Instead of a chemical bath to develop the image, a laser scans the plate and the stimulated phosphors

reveal the image as visible light. The light is converted into a digital format and the image is computed.

The phosphor plates are flexible and can be cut to different shapes.

Direct digital radiography (DDR) – The X-ray image is captured directly on a rigid imaging plate,

which typically is made of either amorphous silicon or amorphous selenium, and the image is transferred directly to a computer as a digital file. No intermediate processing step is needed. 

Types of Inspections

Informational and in-process inspections both evaluate the current condition of a weld or part, verifying if a condition is or is not present. In-process inspections are performed as part of a regular, scheduled inspection cycle; informational inspections are performed as needed. Production inspections

require an approved method to certify or accept a weld or part. Under current standards, film-based

radiography is still required for production inspections.

Radiography:

Film-Based,

Computed,

Direct Digital –

What Is the 

Difference?
http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2 13

curve. Standards for accepting and rejecting inspection results

are still being developed. Although many recurring expenses are

reduced, some still exist and the up-front costs of CR are substantial. Finally, the complexity of CR systems warrants careful

consideration on where they will be located by those planning

to implement the systems.

The Learning Curve

Conventional film-based radiography has well established procedures for carrying out radiographic techniques. These procedures include the amount of radiation, length of exposure and

resulting image quality. Because, as previously noted, CR typically requires less radiation and shorter exposure time, operators need to learn how to optimize the parameters in order to

achieve acceptable results. In addition, the spatial resolution of

the images (i.e., how coarse or fine the image is) affects the

interpretation of the results. There is concern that until training and standards are well established and coordinated, images

potentially could be over-analyzed, and anomalies that would

have been acceptable under wet film processing may now cause

the part being inspected to fail the test.

Standards for Accepting or Rejecting Results

Current accept/reject standards are based on film as well as 

the proven history of how defects will appear in a film-based

system. Changing the capabilities of the imaging system also

changes the predictability of results. Further research is needed to compile a catalog of digital results which are subject to

an analytical process that addresses probability of detection

(POD), probability of failure, desired or expected service life,

etc. This type of work is still in the early stages of progress.

Pending new standards, CR will not be accepted for certain

types of inspections.

System Expenses

At approximately twice the cost, typical CR systems are more

expensive to purchase than film processing systems. In general,

depending upon system configuration, conventional CR 

systems approach a purchase cost of $125,000. It is important

to note that these costs are dropping, while the cost of the 

film-based system is staying the same or increasing. Regarding

recurring costs, each IP costs approximately $550 to $700,

nearly equal the cost for 100 sheets of film. An important difference is that these plates can be reused up to 5000 times.

The IPs require occasional cleaning and other maintenance.

While climate control for the IP storage is not necessary, moisture can be a considerable problem. Moisture and the presence

of dirt and grime will shorten the life of the IP.

There are two pieces of support equipment used for traditional radiography methods that will still be needed in a CR

system. These are film identification units and some type of

storage cabinets for CD-ROMs.

System Location Requirements

The intended installation location should be carefully planned

and evaluated prior to proceeding with the implementation due

to the complexity of CR systems. The temperature of the housing facility should be stable, and there should be no heat

sources (including direct sunlight) within close proximity. As

noted above, moisture and excessive dust and corrosive gases

would also degrade system performance; humidity and ventilation, therefore, should be considered. Constant vibration and

shock must be avoided as well.

COMPUTED RADIOGRAPHY SYSTEMS IN NAVY REGION

NORTHWEST

CNRNW acquired CR systems (see Figure 4) through the

PPEP for three separate Navy activities. Two activities received

their systems in 2003 and have used them for several informational inspections with favorable results. Based on those results,

CNRNW requested an additional system from PPEP for a

third activity; it was installed in early 2006.

Figure 3. A Closer View of the Inspection Results.

Figure 4. An NDI Inspector Uses an IP Reader and Workstation.
14 The AMMTIAC Quarterly, Volume 2, Number 2

Informational inspections have been performed on various

submarine and ship components, and informational verification of defect removal has been performed on various welds. 

In these informational inspections, image quality is not the

defining criterion that it is for production inspections.

Initial work experience suggests that future time and cost savings from using CR should be substantial. In many cases it is

not logistically feasible to use conventional radiography methods to inspect ship components because of the time required

for the inspections while the ship is in dry dock. In one example, the ship components required multiple radiographic

inspections, ultimately ending up with 56 images being taken.

If film were used, each image would have required a 23-minute

exposure time for a total exposure time of more than 21 hours.

Another logistical issue posed by the prolonged exposure times

is protecting the operator and ensuring compliance with

ALARA, which extends the overall inspection time. Given the

available dry dock time for the inspections, this number of conventional radiographic shots for each of these components

would not have been possible.

Using CR for these inspections reduced exposure time to 3.5

minutes per exposure, saving roughly 18 hours in exposure time

alone. In addition to the ALARA-associated benefits of the

reduced exposure, the CR technique allowed operators to quickly read the image plate instead of processing the film. This eliminated retakes, which also saved a considerable amount of time.

Informational CR inspections have already yielded cost and

time savings and with continued effort and research, CNRNW

activities will be at the forefront for implementing this new

technology for inspecting welds and castings. By performing

both a film-based and a CR exposure on the same item, operators demonstrated that the digital images were of the same or

better image quality.

In addition to comparable image quality, operators welcomed the safety benefits associated with the CR process. They

cited the benefits of reducing radiation exposure, eliminating

film-development chemicals, and no longer needing to dispose

of hazardous waste products.

The annual savings for the first CR system have been calculated to be $194,000. This figure is based upon several factors,

including:

• A 500 to 2000 exposure-lifespan for the IP

• Eliminating hazardous waste disposal expenses and the associated cost for silver reclamation

• Saving water by eliminating film rinsing and eliminating 

climate controls for chemicals

• Reduced personnel costs due to reduced exposure times.

In early 2006, the most recent CR system within CNRNW

was installed and manufacturer training was provided; how

ever, the system has yet to be fully utilized. This is a different

CR system from that used at the other activities, and it includes

updated components as well as a selection of three different

sizes of IPs. The new system was installed within an existing

radiography facility, which has spatial limitations that influenced the system’s configuration. Because the radiography

operation is divided between two floors, the radiographic

equipment and scanners were set up on the first floor while the

viewing (reader) stations were placed on the second floor, and

the system components are linked by Ethernet.

Similar to the results from the first two CR systems,

CNRNW anticipates several environmental and workload 

benefits from the implementation of the new CR system. Eliminating chemicals from traditional film development will help

meet the waste reduction requirements under the Resource

Conservation and Recovery Act (RCRA) and Executive Order

13148. In addition, digital imaging will help Navy Region

Northwest reduce its reporting requirements under Superfund

Amendment Reauthorization Act (SARA) Title III. Average

annual savings for the newest CR system are projected to be

$689,000 based on the facility’s return on investment analysis.

Obstacles to Implementation

Regrettably, the Pacific Northwest Navy facilities are not yet

able to fully utilize their CR systems. For these activities, the

use of CR is restricted to the informational type “in-process”

inspections rather than final acceptance inspections. Several

factors contribute to this limitation. The first factor is the 

reliability of weld defect indications. Currently users have 

not consistently achieved the same sensitivity to weld defect

indications with CR as with traditional film techniques.

Process reliability is of paramount importance. The capacity

to certify that individual components are capable of providing

a baseline of information has yet to be established. Related 

to this is the frequency of certification and calibration. Procedures for system certification (including frequency of calibration) have yet to be finalized.

The issuance of standards and authorization depends upon

the completion of two separate studies to examine the present

and future capabilities of CR technology in order to ultimately determine the requirements and procedures for CR inspections. One study is focused on ensuring that the results

obtained through CR are compatible with those obtained

through traditional film processing. The existing operating

practices for technicians are for film-based radiography and

are not directly applicable to CR because of the major technical differences between the two techniques. Any settings alterations under CR affect which discontinuities and anomalies

are detected. The goal is to have a set of procedures that

ensure reliable and consistent detection and evaluation

results, regardless of the operator. The second study is focused

on ensuring that the test results cannot be altered. It is critical that the original data in the digital image files is not able

to be modified.

In addition to Navy authorization, CNRNW activities face

their own obstacles to implementing and using CR. Consolidation of inspection processes among the activities is the primary

obstacle. In addition, once a determination is made on the lead

activity for implementing CR training the two sites will benefit from standardization.

Computed radiography offers several advantages over filmbased techniques, but issues about implementation remain. As

the Navy studies CR applications and requirements in other

settings, Navy Region Northwest will offer its extensive experience to the evaluation.
http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2 15

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