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

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