FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

2.4.2 Repetitive Scanning
- 199 -
The design of a repetitive scan function revolves around maintaining the
shortest overall inspection turnover time. The system reacts to slip and jam
conditions of the probe drive in order to prevent probe and probe cable
damage. Maximum insertion speed of 50 cm/sec and retraction speed of 75
cm/sec and the use of selected speed/location changes allow the fastest
possible speed without signal distortion and cable jamming. The need to
re-scan due to false tube identification is minimized since the system
recognizes when the tube number has not been updated, alerts the operator and
suspends any subsequent scan until updating has taken place.
The operator is alerted to signal deterioration by the calibration signals
that are presented on the first feature of every display. Due to the nature
of the display, signal anomalies can be readily picked out by an analyst,
thus allowing concurrent analysis. An average scan time of roughly 1
minute/tube, provides enough time for such analysis. Also, to reduce
inspection downtime, the system can be temporarily controlled by a single
operator.
The analyst selects a scan parameter set for use, then enters the main
inspection sequence through the menu. The operator then positions the probe
guide at the tube to be inspected and either the operator or analyst
initiates the scan by depressing the scan 'Ready 1 key on the remote keyboard.
As the probe enters the tube, data is collected, displayed and stored on
tape. The insertion sequence terminates with recognition of the tubesheet or
upon reaching a preprogrammed position. During probe insertion the tube
coordinates are entered via the remote keyboard. At the end of the probe
insertion phase the probe automatically retracts, the display hardcopy is
produced and the voice synthesis announces the scan status and tube
coordinates. If the tube number is not entered by the end of the insertion
phase then a 'label' light is lit on the keyboard; the probe still retracts
but the hardcopy and voice synthesis are delayed until the tube coordinates
are entered. The end of printing, voice synthesis and probe retraction to
zero, mark the end of the retraction phase. The operator then repositions
the probe guide and the sequence repeats. During a scan the operator can
stop and start probe motion by using the keyboard. The scan can be
terminated (scan stopped and probe retracted) or aborted (probe drive motion
stopped pending reinitialization) by the analyst through the terminal. The
operator and remote keyboard could be replaced by an automatic tubesheet
walker for scanning tubes in hostile environments such as nuclear steam
generators.
3. SYSTEM OPERATION AND DATA DISPLAYS
3.1 General Operation
System operation begins with equipment setup. A series of calibration scans
would be done, which provides a quick mechanism to calibrate the ET
instrumentation and check overall system operation. The inspection and