FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

3.4 Inspection Scanning
3.4.1 General Tube Scanning
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Scanning can take place as soon as a parameter set has been generated and
calibration has taken place. The repetitive scan task is invoked via the
menu. Entry back to the menu is available to the analyst at the end of each
scan.
A model of a heat exchanger tube is seen in Figure 4. This tube contained
two defects, a dent located under a broach plate and fretting wear (20%
eccentric) under a baffle plate. The calibration tube and retract limit
switch used to zero the distance count are shown.
The printout collected from the mockup heat exchanger tube scan is shown in
Figure 5. The first feature contains the calibration signals. The two
defect signals are easily picked out of the printout. Twelve features were
requested along with tubesheet recognition. The label 'Full Length Scan 1
indicates an inspection scan. The label L:555 denotes that the maximum
length of scan was 555 cm and the label T:555 indicates the tubesheet
recognition stopped the probe at 555 cm. If desired, up to 50 impedance
images could be displayed. If data collection and display could not meet the
0.4 mm data resolution, the message 'Invalid Scan' would be displayed. The
printout can be written upon (analyst notes) and photocopied. A complete,
easy to access inspection record is thus available to reassure the station
manager and regulatory agencies about inspection credibility.
3.4.2 Scan of Selected Tube Regions
The system gives the operator a method of scanning up to 10 tube regions with
expanded signal traces on the X and Y traces of the display. This option,
called 'Expanded Scan', suppresses the signals from tube regions not
requested for display. As in the full length scan, the calibration tube
signals appear in the first feature. An expanded scan display of the two
regions of the mockup tube containing defects appears in Figure 6.
4. VERIFICATION OF ANALYSIS AND INSPECTION PROCEDURE
Verification of both inspection procedure and data analysis requires
recording the original signals and their interpretation as permanent records.
Analog FM recording of data including encoding of tube number, print number
and distance markers, acts as a primary record and retrieval of selected
records is automated. By using the voice synthesized tube number on the
voice channel of the FM recorder, a taped record can be retrieved without the
R'Eddy Record system. The hardcopy printouts of inspection parameters and
data display records with analyst remarks can be bound and act as secondary
records. A third record set is available, comprised of standard strip chart
recordings of data with an ana.log bar code of tube number, print number and
distance pulses on a separate channel. All these records are automatically
generated and make verification a straight forward task.