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

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-
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The AMMTIAC Quarterly, Volume 2, Number 2