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NDT TESTING TIPS FROM NDTECH - NEWSLETTER #15 - March 2000 


This issue of the Newsletter includes:

1. Digital Radiography: A Technology Whose Time Has Come
2. Publications
3. "Sniffers" Expand Law Enforcement's Ability To Detect Explosives And Narcotics

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The NDTech Newsletter is published periodically by NDTech, a consulting firm offering nondestructive
testing, services, and instruments. This newsletter is distributed by email and covers brief descriptions of
some useful but less publicized radiographic, ultrasonic, penetrant, magnetic particle, and other NDT
methods. You will automatically receive the newsletter, at no cost. If you wish to be removed from the
NDTech Newsletter, simply reply with "Remove" as the subject.

To find out more about NDTech and its nondestructive testing consulting services and instrumentation,
visit the NDTech website at http://www.ndtech.net/
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1. Digital Radiography: A Technology Whose Time Has Come

Film-based radiography has a long history and in many respects is an excellent imaging tool. In particular,
film has excellent spatial resolution and, an area detector, supports rapid imaging of inspection objects. On
the other hand, film requires photographic development which can be inconvenient and time consuming,
and may preclude recording changes in objects that occur even moderately rapidly. Film also exhibits a
tradeoff between contrast and dynamic range, making it impossible to image some objects with good
contrast over their full range of attenuation. Film also requires photographic equipment that can be
inconvenient and time consuming, and film processing also poses an enviromental problem.
The emergence of large, fast computer systems and sophisticated image processing software coupled with
the development of solid-state detectors have made digital imaging and real-time radiography both
attractive and feasible, helping propel digital radiography to a position of prominence in aerospace and
other industry applications. Contrast enhancement, spatial filtering, and other image processing can be
performed digitally, and solid-state detectors offer a wide dynamic range. Digital radiography avoids many
of the drawbacks of film radiography. Combining digital radiography with sophisticated and flexible image
processing can provide image quality that in some respects rivals or surpasses that of film.
Digital radiography produces an image similar to a traditional medical X-ray, with internal features
superimposed in the image. Such images are called projection radiographs because they show a plane
view of the object, with internal features superimposed on the image.
In digital radiography, data is collected by moving the X-ray source and detectors linearly along the entire
length of the object; alternately, the object can be moved past the stationary source and detectors-similar
to the technique used by airport baggage inspection systems. Narrow lines of X-ray attenuation data are
collected at brief time intervals. The X-ray measurements are then digitized and displayed as a
two-dimensional image.
A digital radiography image is also similar to a real-time radiography image, although it has a much higher
contrast resolution. This resolution is due to the type of the detectors that are used, which allows as many
as 65,000 intensity (gray) levels to be present in the image.
Four major classes of X-ray detector systems are used in digital radiography:

1. X-ray intensifier tube fluoroscopy system: These systems are widely used in medical and industrial
radiographic applications. Vacuum tube intensifier systems convert X-ray photons into light photons with
a phosphor screen. The light photons are then converted to electrons by a photocathode, and the
electrons are then accelerated to thousands of eV. These accelerated electrons are then focused onto an
output phosphor screen and are converted back to light photons to provide an image. The image is viewed
through a lens with a television camera.
2. X-ray phosphor/vacuum tube low-level-light camera system: These systems do not require image
intensification. The X-ray phosphor does not need to be in a vacuum tube and can even be shaped over
the object. Gadolinium oxysulfide is activated with terbium, a phosphor with a very high X-ray absorption
cross section. Image isocon camera are used with this system since charge-coupled device (CCD) camera
without cooling to have not produced sufficient sensitivity.
3. Linear array scanner system: This system utilizes an X-ray phosphor such as transparent CdWO4 or
CsI single crystals in direct contact with a semiconductor photodiode array. The crystals are cut into
pieces and become discrete pixels in the system. The object is scanned through the fan beam/detector
system, and a computer constructs a line-by-line image. A collimated fan beam/detector system
significantly reduces X-ray scatter compared to noncollimated beams and will produce very accurate
images.
4. Fiber-optic CCD system: A fiber-optic scintillator (FOS) faceplate is used to detect the X-rays and is
made with a luminescent fiber core. The core fibers in the faceplate are 10mm to 20mm in diameter.
When exposed to X-rays, scintillation in each fiber is channeled to the face of the plate, providing a very
sharp image plane that can be bonded directly to a CCD array. The FOS/CCD system offers high X-ray
absorption and improved image acquisition time over typical linear array detection system. This system
can be made lightweight and rugged for scanning of large aerospace structure.

In addition to these four imaging system that have been used over the past several years for digital
radiography, a new flat panel imaging device has recently been developed to meet the needs of the
extremely large medical digital X-ray imaging market. The major distinguishing feature of this new
technology is that electrons are produced directly by the interaction of the X-ray radiation with a flat panel
of material such as amorphous silicon (amSi) or amorphous Selenium (amSe), and the electrons are
directly collected and processes. There are no scintillation or other conversion processes.
With any method of digital radiography, image quality is a direct indication of the ability of a radiographic
process to record images that are representative of the test piece. The quality of a radiographic image can
be defined as the ability of the image to reflect the spatial variations in the attenuation of X-rays by the
examined object. In practice, several factors can degrade the object, including: 1) finite source size, 2)
geometric and spatial resolution, 3) beam scatter, 4) screen or detector absorption and emission
efficiency, and 5) object motion.
The nondestructive evaluation (NDE) uses of digital radiography are varied, including corrosion detection
in aircraft and aerospace systems, metal casting process control, evaluation of advanced composites,
failure analysis of electrical and electromechanical components, inspection of rocket motors, monitoring
containers of weapons-grade plutonium for deterioration, and inspection of welds.
Compared to film radiography, digital radiography technology offers imaging without wet-film processing,
shorter exposure times, a larger dynamic range, and digital imaging. These features, combined with instant
image retrieval and a tolerance for exposure time, offer advantages in field radiography. Recent
advancements in digital radiography have provided X-ray images heretofore unobtainable with
radiographic techniques.
The rapid increase in available data from detector system will require advanced digital hardware and
software to access and manipulate the data. New robotic hardware is also critical in the automation of
more sophisticated production processes. New software will be required for automated evaluation. With
the development of such technology will come radiographic systems capable of automated inspection and
evaluation of such critical defect features as cracks, voids, disbonds, and corrosion in aircraft and
aerospace vehicles.
Advanced digital radiography will play a key role in the NDE of future aerospace components as
automated X-ray inspection of in-process manufactured items provides quality control capabilites not
previously possible. Digital radiography will also play a key role in the inspection of aircraft for cracking
due to stress corrosion. Other applications of digital radiography will emerge as the technology grows and
is proven in practice.
For more information about digital radiography, please contact NTIAC:
NTIAC
415 Crystal Creek Drive, Austin, TX 78746
Phone: (800)NTIAC-39/(800)684-2239
(512)263-2106
Fax: (512)263-3530
Email: mailto://ntiac@access.texas.gov
Website: http://www.ntiac.com

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2. Publications

Nondestructive Testing Handbook,3rd Edition, Vol. 2:Liquid Penetrant Testing-Noel A. Tracy
(technical editor) and Patrick O. Moore (editor). The handbook outlines the principles, equipment,
materials maintenance, methodology, and interpretation skills necessary for liquid penetration testing. The
third edition adds new sections on filtered particle testing of aerospace composites, quality control of
down hole oil field tubular assemblies, and probability of detection, and considers new regulations on CFC
fluids throughout the text.
This book is available from the American Society for Nondestructive Testing at http://www.asnt.org. It is
priced at $181.25 worldwide, $135.00 for ASNT members. This book was published in September 99.

Nondestructive Characterization of Materials IX, Vol.497-Robert E. Green, Jr. (editor). This book is
a collection of technical papers presented at the 9th International Symposium on Nondestructive
Characterization of Materials held June 28 through July 2, 1999 in Sydney, Aulstralia. The papers,
representing the latest developments in nondestructive characterization of materials, are organized by
topic: acoustic emission, electrical, laser ultrasound, magnetic, multiple techniques, optical, thermal,
ultrasonics, vibrational, and X-ray, neutrons, positrons, protons.
This book is available from the American Insitute of Physics at http://www.aip.org or from
http://www.bn.com. It was published in December 1999 and has 732 pages. The book is priced at
$185.00.

1st International Conference on Barkhausen Noise and Micromagnetic Testing Conference
Proceedings. The interest and involvement of researchers and the commitment of those who pursue the
industrial applications of the Barkhausen noise method have been equally important in elevating the
method to its high level today. The papers included in these proceedings cover the theory of the physical
phenomenon of the magnetic Barkhausen effect and the practical applications of micromagnetic testing.
These proceedings are available from America Stress Technologies, 267 Kappa Dr., Pittsburgh, PA
15238-2817, USA; Fax:(412)963-7552. They are available in either book or CD form and cost $40.00.


Nondestructive Testing (NDT) Market Research Reports. Based on questionnaire responses from
over 550 end users, these texts provide information regarding online versus offline testing, NDT spending
by end users , and more. Each volume covers a different aspect of the NDT industry: Vol.1-The U.S.
Market for Film-based Radiography Equipment and Supplies; Vol.2-The U.S. Market for Non-Film
Radiography:Radiography, Digital Radiography, Computed Radiography, and Computed
Tomography;Vol.3-The U.S. Market for Industrial Eddy Current Testing Equipment and Other
Electromagnetic Methods;Vol.4-The U.S. Market for Industrial Ultrasonic Testing Equipment and
Acoustic Emission Equipment;Vol.5-The U.S. Market for Magnetic Particle Testing and Liquid Penetrant
Testing Equipment and Supplies for Industrial NDT;Vol.6-Unabridged composite of Volumes 1 through
5;Vol.7-The U.S. and Canadian Market for Nondestructive Testing Services; and Vol.IR-The U.S.
Market for Commerical & Military Infrared Imaging and Infrared Thermometry Equipment.
These volumes are available from Maxtech International, Inc. 202 Stillson Rd., Fairfield, CT
06432-3227,USA. Phone:(203)362-0165. Website- http://www.maxtech-intl.com.

Ultrasonic Waves in Solid Media-Joseph L. Rose. Ultrasonic wave techniques, used increasingly in
areas ranging from nondestructive inspection of materials to medical diagnosis, evolved from basic
physical principles of wave mechanics. This book brings together basic physics and modern applications.
The author explains the physical principles of wave propagation and then relates them to ultrasonic wave
mechanics and the more recent guided wave techniques used to inspect and evaluate aircraft, power
plants, and pipe-lines in chemical processing plants. Among the topics covered are wave propagation in
plates, rods, hollow cylinders, and multiple layers in solid and composite materials; reflection and
refraction;surface and subsurface waves; and horizontal shear wave propagation.
This book can be found at http://www.cup.org. The book is priced at $90.00 and has 472 pages. It was
published in August 1999.

Nondestructive Testing, Annual Book of ASTM Standards, Vol.3.03-American Society for Testing
and Materials. This volume contains over 150 standards for performing nondestructive testing of
engineering materials, structures and assemblies to detetc flaws and characterize materials properties. The
main subject divisions for the test methods and analytical procedures included in the book are
Radiography, Magnetic Particle and Liquid Penetrant Examination, Acoustic Emission, Ultrasonic,
Electromagnetic, and Leak Testing.
A more detailed summary as well as the book can be found at http://www.astm.org. The book is priced at
$123.00 in North America, $135.00 elsewhere and has 1,074 pages. It was published in November 1999.

Nondestructive Testing Radiography (Programmed Instruction Handbook Series)-Robert W. Smilie
and George Pherigo(editor). This series includes books on the following topics: Film Handling and
Processing, Making Radiographs, Origin and Nature of Radiography, Radiation Safety, Radiography
Equipment, and Nondestructive Testing.
This book series can be found at http://www.amazon.com and http://www.bn.com. The series is priced at
$92.50 and had 1,362 pages. It was published in December 1999. The individual topic can also be found
at http://www.bn.com for $18.50 each.


Flaw Detection and Characterization in Heat Exchanger Tubing-Kenji Krzywosz and Larry Cagle,
Jr. As a collaborative project between Materials Technology Institute (MTI) and the EPRI NDE Center,
an evaluation of nondestructive evaluation techniques was conducted using realistic heat exchanger tubing
mockups in order to assess the inspection capabilities of the various techniques to detect and size tubing
flaws. The evaluation involved seven participating vendors utilizing nine different examination techniques.
Mockups were made of nonmagnetic and ferromagnetic tubing. The techniques evaluated included laser
optic, eddy current, remote field eddy current, IRIS ultrasonic, flux leakage, and NERASON ultrasonic.
Performance of the individual techniques is ranked based pre-established criteria.
This report will be available in May 2000 from MTI Publications. They can be contacted at
mailto:mtiadmin@mti-link.org. The report is priced at $40.00 for nonmembers.

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3. "Sniffers" Expand Law Enforcement's Ability To Detect Explosives And Narcotics

Researchers at the Department of Energy's Sandia National Laboratories have developed a handcarried
device that, like a trained police dog, could sniff out the faint odors of drugs and bombs ar airports,
border crossings, military installations, and schools. The portable device is a miniaturized version of an
explosives-detecting walk-through portal Sandia developed for the Federal Aviation Administration (FAA).
The portal, which blows a puff of air over a airplane passenger and checks for minute levels of explosives
in the airflow, might soon be seen at U.S. airports as a security-screening tool.
Recent improvements in the portal's underlying chemical preconcentrator technology are enabling
ever-smaller sniffing tools. Miniaturization of the preconcentrator allows the development of smaller
detection tools that are portable, cheap, sensitive, and fast.
For more information about the portable air sniffer, contact Kevin Linker, mailto:kllinde@sandia.gov.

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Copyright 1999 NDTech.






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