AMMTIAC Quarterly, Vol. 2, No. 2 - Advanced Materials ...

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
Meet Our New
Director
Mike Morgan
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
Editor-in-Chief
Benjamin D. Craig
Publication Design
Cynthia Long
Tamara R. Grossman
Copy Editor
Perry Onderdonk
Information Processing
Caron Dibert
Inquiry Services
Richard A. Lane
Product Sales
Gina Nash
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
Secretary of Defense, Director of Defense Research and Engineering (DDR&E). The AMMTIAC Quarterly is
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:
Micheal J. Morgan
Director, AMMTIAC
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AMMTIAC
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EMAIL: ammtiac@alionscience.com

George A. Matzkanin
H. Thomas Yolken
AMMTIAC
Austin, TX
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
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).
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 (

Amplitude
150
0
-150
0 50 100 150
time(µs)
150
Figure 2. Waveforms for a Three-Layer Structure, Aluminum-
Adhesive-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.)
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
Receiving
Module
RITEC
RAM-10000
Gated
Amplifier
Amplitude
(a)
0
-150
Charge Amplifier
Simulated Hidden Corrision
Test Plate
AC/DC
Decoupler
200V Bias
Transmitter
Receiver
Control/Acquisition
Computer
Monitor Signals
Oscilloscope
Figure 3. Experimental Setup for Gas (Air) – Coupled Ultrasonic
Guided Wave Detection of Thinning Defects in Aluminum Plates.[7]
Amplitude
(c)
150
0 50 100 150
time(µs)
0
-150
(b)
0 50 100 150
time(µs)
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 (OC-
ALC) for the detection and quantification of intergranular corrosion
100
90
80
70
60
50
40
30
20
10
0 Eddy Current A Eddy Current B Ultrasonic Testing Dripless Bubbler
(Sierra Matrix)
Dripless Bubbler
(ISU)
Thermal A
Hit % – Within Shadow Hit % – Beyond Shadow False Call Rate
Thermal (Wayne
State Univ.)
Figure 4. Corrosion Detection around Wing-Skin Fasteners –
Chemically Induced Intergranular Corrosion Trial Results.[10]*
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
4
The AMMTIAC Quarterly, Volume 2, Number 2

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
Transducer
Incident Beam
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.
Figure 5. A Schematic View of the Wavefield in a
Painted 2-Layer Structure.[15]
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)
Excitational
Coil
Specular Reflection
Non-Specular Reflection
Corrosion
Figure 7. Two Energy Coupling Paths in a Remote
Field Eddy Current Probe for Pipe Testing.[19]
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
Paint
Skin
Primer
Bond
Substructure (Stiffener, T-Cap, Stringer, etc.)
Indirect Energy Coupling Path
Direct Energy Coupling Path
Indirect Energy Coupling Path
Pick-up
Coil

6
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.
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.)
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.

techsolutions 5
Brett J. Ingold
AMMTIAC
Rome, NY
A Selecting Brief Introduction a Nondestructive to Precious Testing Metals Method, Part IV: Radiography
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
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.
Beam
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
Flaw
Radiation Source
Test Piece
(Object)
Medium for
Converting
the Radiation
Image of Flaw
Figure 1. Diagram of Typical
Radiography Test Setup.[2]
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.
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7

techsolutions 5
X-Rays
Visible
10 -2 10 2 10 4 10 6
Gamma Rays Ultraviolet Infrared
Wavelengths in angstrom units (A), where 1 A = 10 -8 cm = 3.937x10 -9 in.
Figure 2. Electromagnetic
Spectrum Showing X-ray and
Gamma Ray Regions.[1]
10 0 A review of radiographs from an F-15 Eagle to
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
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)
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
check for foreign object debris and cracks
in the aircraft's structure. (Photo taken by
Staff Sgt. Shelley Gill and provided courtesy
offers the ability of US Air Force)
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 problemat-
8
The AMMTIAC Quarterly, Volume 2, Number 2

AMMTIAC
A DVANCED M ATERIALS, MANUFACTURING AND T ESTING
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
General
with X-rays Radiography with γ-rays with X-rays Radiography with γ-rays
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 3 2 3 3 2
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
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.
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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
(e.g. what types the method can detect)
Size of discontinuities
Limitations
Advantages
Inspector training (level and/or availability)
Inspector certification required
Equipment
Relative cost of inspection
• Voids
• Inclusions
• Cracks
• Non-uniformity of material
• Density changes
• Weld defects
• Discontinuities that exhibit 1% or more absorption difference relative to surrounding region
• Advanced systems can detect flaws as small as 0.001 inches
• 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
• 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
• Variety of programs available nationally to study the science of radiology
• Radiation safety training is critically important
• ASNT offers certification for radiography safety
• Portable or fixed setups depending on industry/company requirements and desired function
• Traditional radiography requires film development facilities and equipment
• Depends on setup, but cost can be greatly reduced with the use of portable equipment
that requires less space
10
The AMMTIAC Quarterly, Volume 2, Number 2

Greg A. Levcun
Naval Facilities Engineering Command Northwest
Christopher S. Mahendra
Naval Air Systems Command
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.
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.
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.
Figure 1. An NDI Inspector Works with the
IP and Reader.
Figure 2. An Inspector Looks at Two Views
of a Defect.
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.
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11

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:
Film-Based,
Computed,
Direct Digital –
What Is the
Difference
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.
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The AMMTIAC Quarterly, Volume 2, Number 2

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.
Figure 3. A Closer View of the Inspection Results.
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 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 4. An NDI Inspector Uses an IP Reader and Workstation.
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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.
14
The AMMTIAC Quarterly, Volume 2, Number 2

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