Operating Manual

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Although the electronics needed for both methods, e.g. workstation, cost approximately the
same (and partly can be shared!), a flat panel detector (~ € 150,000 ) is roughly 200 times
more expensive than a phosphor plate (~ € 750 ). Hence selection of a DR solution requi-
res careful considerations with regard to return of investment (pay back period). Another
aspect of paramount importance, which influences selection between CR and DR, is the
availability (or lack) of industrial standards.
In summary: Numerous aspects with a great diversity such as: image quality, process speed,
productivity, portability, robustness/fragility, (in)flexibility of plate or panel, available field
space, logistics, environmental issues, capital investment, human investment, (non)existence
of industrial standards etc. play a role in the ultimate choice between conventional film or
CR or DR .
16.11 Applications of CR- and DR methods
Corrosion detection
For certain applications, e.g. when the requirements for image quality are less stringent and
normal or coarse-grain film could be used, the CR technique is an excellent alternative to
film. Examples include profile (on-stream) radiography, the majority of the work in 2008
(using isotopes) to detect general internal erosion or corrosion of non-insulated piping, see
figure 28-16 and detection of internal and external corrosion under thermal insulation
(CUI) see figure 29-16. For wall thickness determination of (insulated) pipes the so-called
projection (shadow technique) or tangential technique is applied, see section 18.6.
CR is also very suitable for detection and quantification of erosion/corrosion in or adjacent
to the root of welds and for detection and quantification of scaling or clogging, concrete
inspection and non-critical castings. In case of offshore work CR is attractive using low acti-
vity sources first of all because its smaller controlled area and secondly to avoid that level
detectors using radiation are falsely activated or disturbed.
Weld inspection
Although conventional film is still superior compared to the CR technique, standards permit
CR in several cases because it can under circumstances provide sufficient image quality,
even for weld inspection, see section 16.9. Figure 30-16 shows an image of a weld with a
clear indication of a serious longitudinal defect.
Dose reduction and controlled area
Not only are CR- (~ 5x to10x) and DR techniques (~ 20x with film-quality, to 200x with
low quality) much faster than standard X-ray film exposures, (see figure 27-16) another
attractive feature is their far greater dynamic range/latitude (> 1000x).
These methods are, therefore, not over-sensitive to variations in radiation dose and very
tolerant to less than exact exposure times, see figure 8-16.
This can reduce so-called re-shoots (retakes) and can decrease the need for multiple expo-
sures of some parts with different thicknesses, thus further improving inspection throughput.
The reduced exposure times - in practice a factor 2 to10 dependent on the type of plate
- or weaker sources that can be used, are deciding efficiency- and safety factors (smaller
controlled area). The controlled area (radiation exclusion zone) reduces with the square
root of source strength ratio:
source strength 1 ÷source strength 2
Note: For a given application the source activity/strength (Bq) can be reduced, but not its
energy level (MeV/keV) because it is the energy level that determines the penetration
capability.
Fig. 28-16. CR image of bare pipe with areas marked
for WT measurements
Fig. 29-16. CR image of insulated pipe with WT-values
Fig. 30-16. CR image of a weld with a longitudinal defect see acknowledgements*
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Defect Defect Defect