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OT10 (2010-4-5)
 
Advanced Visual Testing Technologies for In-Vessel Inspection
 
Yoshinori Satoh
Inspection System Technology Group,
Nuclear Instrumentation and Inspection Technology R&D Department,
Power and Industrial Systems Research and Development Center,
Power System Company,
Toshiba Corporation
 
KEYWORDS:
In-Vessel Visual Inspection, Image Processing, Super Resolution, 3D Vision
 

Full Download( PDF)
slide
 
  1. Advanced Visual Testing Technologies for In-Vessel Inspection
Yoshinori Satoh1), Jun Suzuki2), Toru Ootsubo2)
1) Power and Industrial systems R&D Center,
2) Isogo Nuclear Engineering Center,
Power Systems Company, Toshiba Corporation
July 26, 2009
  2. Background
  In-Vessel Visual Inspection (IVVI) as ISI based on the JSME S NA1–2004 :The following reactor internals is inspected by VT-3 for the standard inspection;
  »Core Shroud;
  »Jet pump;
  »Shroud support;
  »Top guide, Core plate and so on.
Individual Inspection for reactor internal is also needed;
  »Inspection for stress corrosion cracking;
  »Long interval compared to standard inspection (ex: 10years, 25years)
  »EVT-1 should be used for the individual inspection;
Enhancement of NDE technique is required;
  »Advanced VT technique to achieve high accuracy;
  »ECT or Laser-UT as alternative inspection for visual;
  »High accuracy Ultrasonic testing (PA UT technique); and,
  »Delivery and positioning technique.
  3. Overview of TOSHIBA IVI Technologies
  Phased Array UT
  »High accuracy flaw depth sizing on weld surface by immersion technique.
Laser UT & ECT
  »High resolved flaw detection and length & depth sizing in the reactor water.
Advanced VT
  »Super Resolution VT system 
  »3D VT system
  4. Phased Array UT
  Principle
Ultrasonic beam is steered and focused by phase controlled excitation of multiple array elements
Feature
● Real time B-scan image carried out  for objective region
● Inspection condition can be changed according to defects and objective components
● Focused longitudinal wave is effective for inspection of welds
● Immersion technique is not affected to the surface condition
  5. Laser UT – PWR BMI
  6. Remotely Operated Vehicle (ROV) - Lineup
  7. ROV - Features
- Applicable to in-vessel inspection and pool inner wall inspection with highly accurate positioning capability.
Shroud ROV
・Accessible to 55 mm and more;
・Demonstrated to EPRI;
・Multi purpose use attaching various head (e.g. UT and Brushing).
Shroud Support ROV
・Drive below baffle plate
・Demonstrated to EPRI;
・Multi purpose use attaching various head (e.g. UT and Brushing).
Small Vehicle
・Approximately Dia. 140mm (Main body);
・Accessible to entire surface to be inspected;
・Demonstrated to EPRI;
・Manual operation;
・Stable by touching wheels on target.
  8. Operating Experience
  9. Advanced VT Technologies
10. Requirement for VT technologies
  Visual Testing (VT) for IVI
・ VT is usually performed as “indirect” visual inspection using remote cameras because target objects are under water and in high radiation area.
・ Inspectors detect cracks on surface of internal structures on the monitor.
11. Requirement for VT technologies
  Visual Testing (VT) for IVI
Motivations
・Simplifying adjustment works
・Enhancing visibility on the monitor
・Providing intuitive visual interface
12. Super Resolution Technique
Example result of Super Resolution processing
13. Overview of Super Resolution Technique
Principle of SR
14. Overview of Super Resolution Technique
Effects by applying Super Resolution (SR)
- SR can make higher resolution images from a low resolution video. This behavior is equal to making camera close to objects. → SR can reduce difficult camera adjustment works such as making cameras close to objects in narrow space. In other words, SR can reduce VT time.
- SR can be performed without expensive hardware but with software. → It can prevent from increasing in cost.
- SR can enhance the resolution of VT video ONLY from frames in the video without additional information.→ SR has applicability to visual inspection activities.
15. Overview of Super Resolution Technique
Algorithm construction for Super Resolution Imaging System
16. Experimental Results
Experimental Configuration
17. Experimental Results
Case 1
SCC Test Piece
Condition
- Working Distance: 195mm
- Field of View: 50mm×38mm
- Resolution: 70μm/pixel
18. Experimental Results
- Raw Video (Part of Test Piece)
- SR image (Part of Test Piece)
SR processing can enhance the crack in higher resolution
19. Experimental Results
Case 2
Cylindrical Test Piece
Condition
- Working Distance: 293mm
- Field of View: 100mm×75mm
- Resolution: 156μm/pixel
20. Experimental Results
- Raw Video (Part of Test Piece)
- SR image (Part of Test Piece)
SR processing can enhance thin wire in higher resolution.
21. Experimental Results
Case 3
Cylindrical Test Piece
Condition
- Working Distance: 586 mm
- Field of View: 150mm×113mm
- Resolution: 234μm/pixel
22. Experimental Results
- Raw Video (Part of test piece)
- SR image (Part of test piece)
SR processing can enhance thin wire in higher resolution.
23. Applicability Evaluation
Quantitative Evaluation of Super Resolution (SR)
In order to evaluate applicability of SR “quantitatively”, we conducted visibility evaluation based on VT-1 grade of ASME.
※ VT-1 must be demonstrated capable of resolving characters whose height is 1.1mm.
24. Applicability Evaluation
Definition of Quantitative Visibility
For the evaluation, we compare the visibility of the characters on Super Resolution (SR) images to that on raw videos.

Visibility
arrow
Readability: Ratio of the number of VT-1 characters which 3 examiners could read to the number of all test characters.

Readability (%)
= (Number of characters which examiners could read) /(Number of all test characters)×100(%)
25. Applicability Evaluation
Experimental Configuration
(a) Comparing readabilities while changing working distance
(b) Comparing readabilities while changing scanning speed
26. Applicability Evaluation
- Comparison result while changing WD when scanning speed is 10mm/sec
27. Applicability Evaluation
- Comparison result while changing scanning speed when WD=200mm
28. Applicability Evaluation
Summary of evaluations
We can confirm that the use of the Super Resolution (SR) brings the following effects.
- It will be able to become easier and more flexibly to set the working distance of cameras in VT because SR can give nearer images with software.
- SR will be able to prevent camera motions from reducing visibility on monitor.
29. 3DVT Technique
3-dimensional VT (3DVT) technique is based on Stereo vision.
Some information can be provided …
(1) Crack length and etc. on 3D path
(2) 3D shapes (wire-frame, surface and texture model)
(3) Cross-section view on reconstructed object surface
Main Processes are …
(1) camera calibration (relative camera position and angle)
(2) image matching of 2 images from each camera
(3) 3D-coordinates calculation using image pixel and camera parameters
30. Overview of 3DVT Technique
Configuration of this system with 3D camera head, control device and processing device:
- 3D Camera head is consist of 2 camera and rotating table.
- Control Device is for signal communication and operation.
- Processing Device perform image processing, calibration and 3D-measurement process.
31. 3D Camera for Flat Target
32. 3D Camera for Flat Target
Configuration of 3D Camera Head
Surface Shape Measurement Result
33. 3D Camera for Pipe Target

Measurement target
(1) Welding part of CRD Housing and CRD stub tube (J-weld)
(2) Welding part of CRD stub tube and RPV (3D-weld)

In order to measure welding part of CRD stub tube …
Restricted conditions
(1) To mount on access device for being possible to scan and measure
(2) To able to access and measure in a narrow space
(3) To fix working distance (250mm in air)

34. 3D Camera for Pipe Target
Configuration of prototype measurement head
Camera: 640x480pixels, 1/4 inch (6.4mm) CCD
Head Size: 50mm(L)x70mm(W)x30mm(D)
Measurement accuracy (depth): 0.5mm
35. 3D Camera for Pipe Target
Results of Mockup Experiment
Both welding parts (J-weld and 3D-weld) of the Mock-up were able to be measured surface shape of welding part.
We can confirmed that our 3DVT technique and prototype measurement head were effective.
36. Flexible 3D Camera System
Main functions
Covering from micro measurement (crack length) to macro measurement (position, distance, level of internal structure) for Jet-pump
Specifications
(1) Measurement accuracy (depth): 0.5mm (WD= 100mm), 5.0mm (WD = 600mm);
(2) Field of view: 100x75mm or more

37. Flexible 3D Camera System
Remarkable points
(1) Working distance is variable change as rotating camera
(2) Cross point of optical axis is adjusted most suitable angle automatically
(3) Size measurement covering from tiny crack to large structure
(4) Measuring distance on 3D path and direct distance between 2 points
38. Flexible 3D Camera System
Example of 3D measurement (Main GUI)
39. Flexible 3D Camera System
Example of 3D measurement using zoom
A measurement result of a test piece which has welding part (Working Distance: 350mm)
40. Flexible 3D Camera System
Applicability Evaluation of Flexible 3D Camera
A measurement result of a test piece which has welding part (Working Distance: 350mm)
41. Applicability Evaluation of Flexible 3D Camera
Applicability Evaluation of Flexible 3D Camera
In order to verify applicability of this 3D VT system, we performed 3D measurement for the surface of Jet pump mock-up in full scale tank.
42. Flexible 3D Camera System
Measurement Result of Jet Pump Mock-up
We can confirm that the profile (cross-section) data on the Jet Pump surface was obtained along cylindrical surface.
43. Flexible 3D Camera System
Downsizing of proto-type 3D Camera head for narrow space
44. Flexible 3D Camera System
- Developed the prototype measurement system by the 3DVT technique for shape reconstruction and crack length measurement.
- Result of std. is less than 0.5mm (measurement resolution in design). Confirm to able to measure difference in level of 0.5mm.
- Conducted mock-up experiment for demonstrating the effectiveness of 3DVT technique and the applicability of prototype measurement head of this system using simulated test piece of actual equipment shape.
45. Conclusion

Toshiba has various advanced NDE technologies, such as phased array UT and Laser-UT, and widely applies these technologies to actual in-vessel inspections for nuclear power plants.

In particular, distinctive VT technologies have been developed;
- Super resolution (SR) VT enables to produce a still image having 3 times better resolution from original low-resolution video data.
- 3-dimensional (3D) VT enables to quantitatively reconstruct object shapes with an accuracy of 0.5mm.


EJAM OT10: "Advanced Visual Testing Technologies for In-Vessel Inspection" by Yoshinori Satoh (Power System Company, Toshiba Corporation)