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

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.
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The AMMTIAC Quarterly, Volume 2, Number 2