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Computed Radiography |
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| Why Digital Radiography?
– Radiography without film or chemicals |
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 almost universally adopted by medical/dental professions
extensively used in military and aerospace industries
meets API 1104, DnV OS F101, ASME VI etc
more flexible than film RT or autoUT
lower-cost alternative with equivalent or better quality
single image, less complex, simple interpretation
no special operator training
(top) |
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| Has Digital Radiography
been accepted? |
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Digital Radiography is a mature technology.
Digital radiography is clearly an alternative to film.
ASTM subcommittee E07.01
“The benefits of having an industrial
radiographic process without the cost associated with film,
photographic chemistry, environmental compliance and film
storage are further enhanced by the ability to achieve the
required results in less time, at lower doses of radiation,
using digital archiving and the ability to network.”
TWI, PR6573 Computed Radiography JIP, Oct 02
cost savings
over film with re-usable imaging plates
communicating
images electronically
elimination
of darkroom and chemical developer process
reduction
in radiographic intensities (kV)
reduced
exposure times (particularly for gamma)
easily customised
for field radiography
analysis
using advanced imaging and defect recognition algorithms
US Navy – Aviation equipment program (PMA-260), Dec’04
US Navy Air service have stated they intend to fully implement
a switch to digital radiography by 2007 based upon the following
considerations:
because
imaging plates can record more information than film, greater
in-depth analysis and manipulation can be performed from
a single shot. Expands viewable density range by three to
four times over conventional film;
annual operating
costs of the digital radiography system are projected to
be one-sixth of the conventional system
the hazardous
materials and hazardous waste associated with film development
are eliminated
Digital Radiography is allowed by the main piping/pipeline codes
| API
1104 19th Edition |
Welding of pipelines and related facilities, Sep’99
Para 11.1.2.3 - Other imaging methods |
prEN
14784
Part 1
Part 2 |
Industrial Computed Radiography with phosphor
imaging plates, June’04
Classification of Industrial Computed Radiography systems
General principles for examination of metallic materials
using x-rays and gamma rays |
| DnV
OD F101 |
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| ASME
– E2002 |
Standard Practice for determining total image unsharpness
in radiology |
| ASME
– E2003 |
Standard Practice for Computed Radiology |
| ASME
– E2007 |
Standard Guide for Computed Radiology |
(top) |
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| What is Computed Radiography? |
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a digital radiographic technique that uses photo-stimulable
phosphor plates (PSPs) instead of film to capture images
PSPs are flexible and can be wrapped around the pipe
following exposure the PSPs are scanned and a high-quality
digital image is obtained
the image is then viewed, modified (if required), analysed
and archived using the TõmõRad Digital light-box®
(top)
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| How does Computed Radiography work? |
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Animation soon available
| step 1 |
PSP put into cassette (with or without lead screens) |
same as with film |
| step 2 |
a radiation pattern is exposed on the PSP creating a latent
image |
same as with film |
| step 3 |
the PSP is then fed into the scanner to be read, the PSP
can then be erased and re-used |
Film is placed into to auto developer which is similar
operation to a scanner |
| step 4 |
the digital image is instantly displayed on a monitor
for viewing using Digital light-box® |
Film has to be developed and dry before it can be read
on a light-box |
(top)
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| What are the benefits from CR compared with film RT |
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| cycle-time |
PSPs are 10x more sensitive than film allowing reduced
exposure times. Plates can be scanned and produce digital
images in less than one minute. Auto-interpretation improves
consistency and saves time |
| environment |
The process uses less consumables (film and developer
chemicals) and generates no waste (spent developer chemicals
are classified as hazardous due to heavy-metal content).
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| safety |
PSP sensitivity extends the range of wall thickness
over which safe radiographic technique, using Se75 source,
can be used
Film – 10 to 25 mm PSPs - 10 to
80 mm |
| Cost |
Process is cheaper as it saves film and developer cost
Shorter cycle-time - improved productivity leading to
lower cost
Portable equipment – can be transported in flight case
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| Quality |
Comparable image quality to film – enhanced interpretation
capability
QC checks built in to software less reliance upon inspectors
Digital back-up and archiving (to DVDs) |
(top)
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| What are the benefits from CR compared with autoUT
– Using
CR and advanced software Tomorad aim to raise the standards against
which autoUT is compared
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| cycle-time |
Computed Radiography cycle time is generally less than
three minutes. Interpretation, aided by software, is less
and less prone to over-size defects. |
| safety |
Using a safe radiographic technique (Se75 and the appropriate
Tungsten shielding) the exclusion zone is less than 2m.
CR can safely be used in confined spaces such as the back-end
of a lay barge or a J-lay tower. |
| logistics |
An autoUT spread comprises a lot of expensive equipment
and it requires a constant source of fresh water for couplant.
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| cost schedule |
Signifcantly cheaper to operate than auto UT both in
terms of CAPEX and OPEX. No long lead for manufacture
of calibration blocks and qualification of procedures.
Lower cost support personnel – no Prima donnas! |
| quality |
CR produces an image which, in addition to measurements,
allows a more qualitative assessment of the weld. CR has
a higher PoD than film radiography and has been shown
to find flaws that autoUT cannot find |
Radiography remains the yardstick against which other volumetric
inspection techniques are judged
autoUT is prone to false-calls and tends to oversize defects
leading to unnecessary repairs and cut-outs
“autoUT should have a low false-call rate as compared with
RT”
qualification of the autoUT procedure requires RT of the
welds
Construction industry standards require autoUT performance
to be at least as good as radiography in revealing significant
defects
(top)
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| ROC analysis |
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(top)
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| Cost comparison – CR vs film
; Following cost comparison
has been adapted from TWI JIP – Demonstrates that CR offers improved
productivity, digital archiving and pay-back in under 6 months |
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CAPEX for CR comparable to automatic film system
CR almost eliminates consumable cost (film, chemicals etc)
with CR no hazardous wastes to store and dispose of
Reduced labour/costs for handling and archiving films
| Film radiography |
no |
Unit |
Unit cost |
year 1 |
year 2 |
| automatic developer + spares |
1 |
Ea |
30,000 |
30,000 |
8,000 |
| film (per/100) |
25,000 |
/100 |
350 |
87,500 |
87,500 |
| developer chemical costs |
52 |
/wk |
50 |
2,600 |
2,600 |
| silver recovery system |
10 |
hr/wk |
40 |
20,800 |
20,800 |
| chemical waste disposal |
60 |
/wk |
60 |
3,600 |
3,600 |
| film archiving (space + labour) |
1 |
/yr |
15,375 |
15,375 |
15,375 |
| administration (film indexing) |
17 |
hr/wk |
40 |
35,360 |
35,360 |
| Film |
total |
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195,235 |
173,235 |
| Film radiography |
no |
Unit |
Unit cost |
year 1 |
year 2 |
| CR system (scanner, PC, monitor) |
1 |
Ea |
45,000 |
45,000 |
6,000 |
| Software + back-up system |
1 |
Ea |
25,000 |
25,000 |
2,000 |
| PSPs (50% annual replacement) |
12 |
Ea |
350 |
4,200 |
2,100 |
| Consumables (DVDs) |
7 |
/wk |
2 |
728 |
728 |
| administration (on PC) |
10 |
hr/wk |
40 |
20,800 |
20,800 |
| CR |
total |
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95,728 |
31,628 |
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| Potential saving (CR vs film) |
99,507 |
141,607 |
(top)
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| Cycle time comparison – CR vs film |
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| Activity |
Film RT |
CR |
Note |
| align crawler/source |
0:30 |
0:30 |
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| place film/PSPs |
0:20 |
0:00 |
using Aerogel weld shields no need to wait for weld
to cool before placing PSPs |
| Exposure |
0:40 |
0:10 |
PSPs are up to 10x more sensitive than film requiring
shorter exposure |
| Remove cartridges to dark-room |
0:20 |
0:20 |
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| Develop/scan images |
4:00 |
1:00 |
based upon interpretation of dry-film |
| interpretation/sentencing |
1:00 |
0:30 |
assumed auto-interpretation by Digital-light-box® |
| Total |
6:50 |
2:30 |
Time saving 4:20 |
(top)
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| Display screen myths |
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capability to interpret radiographs is limited by the capacity/acuity
of the human eye which is:
 pixel depth: 8-9 bits or 64-128 shades of grey
Spatial Resolution: 8-10 lp/mm
an industrial radiographer is not required to perform diagnostic
interpretation in the same manner as a physician/radiologist.
zoom-function within the
Digital light-box® obviates a requirement
for Medical standard screens (3-5 MB QSXGA or higher)
using computed radiography the processor evaluates an image
of 16 bit (4096 grey shades) with >10lp/mm resolution, and
thus can detect items that would possibly be overlooked by
human inspection. Theoretically the inherent the accuracy
and repeatability offered by computer defect detection algorithms
at least meets or even exceeds the visual acuity of the interpreters.
(top)
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| Computed Radiography equipment |
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| Source |
Either low power x-ray tube or gamma source may be
used (Se75 is preferred both for personnel safety and
the resulting image quality). |
| Image capture |
Radiographic images are captured using re-usable, photo-stimulable
phosphor imaging plates (PSPs) in place of conventional
film. |
| Developer |
Following exposure, the plates are scanned using a
red-light laser in order to generate a digital image.
Once the image has been acquired the plate is erased by
exposure to bright, white light. |
| Viewer Light-box |
The images are stored on a high-end PC equipped with
a high definition screen. Software allows manipulation
and enhancement of brightness, contrast, magnification
etc) |
| Archive |
Digital image files are stored on a secure hard-drive
with auto-back-up facility. Periodically the images can
be written to DVD for long-term archive. |
(top)
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| How do PSP work? |
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Animation soon available
Henri Becquerel, the French physicist, first discovered photo-stimulated
luminescence (PSL) in 1875. However it was not until 1981
that Fujifilm introduced the first commercial CR system
PSPs consist of a polyester base coated with a crystalline
halide emulsion (Europium activated, Barium flouro-halide
–BaF.X:Eu2+ where X = Cl, Br or I)
incident ionising radiation creates a colour centre in the
crystalline lattice where an electron becomes trapped, thus
storing energy.
when the plate is scanned with a high-intensity, red-light
from a Helium-Neon laser, blue-light is emitted which is then
captured and intensified in a photomultiplier tube.
(top)
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| Computed Radiography can use either X-ray or gamma-sources |
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| Source/isotope |
Gamma energy (k.eV) |
Half-life (days) |
Gamma constant |
Working range with steel |
| Cobalt |
60Co |
1170-1330 |
1925 |
1.3 |
50-150 |
| Iridiun |
192Ir |
206-612 |
74 |
0.48 |
12-63 |
| Selenium |
75Se |
97-401 |
120 |
0.203 |
3-29 |
| Ytterbium |
169Yb |
63-308 |
32 |
0.125 |
2-20 |
(top)
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| Preferred source is Selenium |
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radiographic safety, exclusion zone of 1-2 m instead of 30-50m
applicable over wide range of pipeline wall thickness
reduced inherent film un-sharpness due to lower spectral
energy
improved specific contrast for detection of defects
(top)
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| Environmental issues |
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Film radiography generates several wastes
Lead found in foil-packets and discarded screens
Silver found in spent fixer solution
Chromium which is used in cleaning products
all of the above are represent a hazard to the environment
Film radiography generates several wastes
Lead found in foil-packets and discarded screens
Silver found in spent fixer solution
Chromium which is used in cleaning products
all of the above are represent a hazard to the environment
(top)
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| Overall comparison between autoUT, CR si RT |
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Film Radiography
Expensive Running costs (film/chemicals)
Testing can be performed immediately
Need to evacuate area
Suited for small batch or long production
Minimum training required (Retrain radiographers)
Simple qualification programs
Understandable image
High radiation exposure
Long exposure
Film quality less and archiving difficult
AUT
Expensive initial setup
Complicated
Expensive Running costs
Long lead in time, cal block manufacture
Numerous blocks required (thickness/Dia/material)
Best suited to long trunklines,
Intensive training required
Elaborate qualification programs
Expensive technicians
Difficult to understand images
Computed Radiography
Inexpensive Running costs
Testing can be performed immediately
Suited for small batch or long production
Minimum training required (Retrain radiographers)
Simple qualification programs
Understandable image
Low radiation exposure
Short exposure
Better S/N ratio than film RT
(top)
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| Computed Radiography Benefits |
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Provides immediate startup
Versatile in Application
Safe working environment
Work within 2 metres*
Meets ASME/AWS/API
Current equipment usable
Current Xr personnel
Digital image and archiving
No chemicals/film
Versatile imaging software
Auto markup of flaws
Auto calculation of flaw accumulation and size
Auto reporting
Remote audit possible
Detection
better than film RT
As good as AUT
(top)
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