|TABLE OF CONTENTS|
This paper presents the results of part 1 of feasibility study using linear-array probes and advanced data analysis software. The following topics will be discussed:
RDTech-Quebec City and Ontario Hydro - SIMD-Pickering performed the first part of feasibility study. Companies from France and Canada contributed with specific tasks to this project. Some input regarding ray tracing, probe development and engineering assessment was received from companies / institutions from USA, Scotland, Switzerland, Sweden, Japan, Germany and Spain.
The first 75 mm from inlet-outlet face were inspected, using two linear probes and three techniques. The synthesis of these UT results will be presented to this workshop.
Figure 1: Ultrasonic techniques used in feasibility study with linear array probe.
A variety of reference blocks, from simple to complex shapes, were manufactured and EDM notches were placed in the platform / hook areas. Table 1 listed the blocks used for probe characterization and detection / sizing assessment.
Reference blocks used for probe characterization and detection / sizing.
|Block ID||Thickness / reflectors||Scope|
|IOW modified||75 mm / SDH||Probe characterization|
|RDTech-S1||120 mm / SDH||"|
|NS-2||27 mm / FBH||"|
|NS-4||1-11 mm / FBH||"|
|NS-5||16 - 27 mm / FBH||"|
|Oblique block||120 - 250 mm / EDM notches||Detection / sizing|
|Block #1||130 mm / EDM notches||"|
|Block #2||130 mm + 80 mm wing / EDM notches||"|
|Block # 3||130 mm + 80 mm half wing / EDM notches||"|
|" Silver" blade L-0||130 mm / EDM notches||"|
|Spare blade L-0||130 mm||Comparison study / detection|
An example of L-0 blade mock-up is presented in Figure 2.
|Figure 1: Ultrasonic techniques used in feasibility study with linear array probe.||Figure 3: Ray tracing model simulating a detection of a linear defect 6 mm x 2 mm, located at 50 mm on hook # 1, from the inlet face, using technique # 1 and focused probe.|
The main features of phased-array probes.
|Feature||Probe # 1||Probe #2|
|Center frequency||7 MHz||11 MHz|
|Range||10 - 110 mm||1 - 25 mm|
|Skew angle||± 60°||± 30°|
|Number of elements||32||20|
|S / N for technique 1||> 12 dB||> 16 dB|
|S / N for technique 2 / 3||> 30 dB||> 36 dB|
Two prototype linear array probes were designed and manufactured. The main features of these probes are presented in Table 2.
The following hardware was used: Tomoscan 3.5R8, Focus 32 / 64 piezo-composite phased array driver, MDU, Traker and Rover manipulators. RDTech-Quebec City manufactured the all above-mentioned hardware.
|Figure 4: Data analysis and 2-D plotting into reference block dimensions. A 6 mm x 2 mm EDM notch on hook #3 was sized as 6.2 mm x 1.8 mm, and located within 1.4 mm in all three coordinates of the specimen.||Figure 5: Detection and UT display in multi-scan of two EDM notches in block #1.|
The first probe could size EDM notches within an accuracy of about ± 1 mm for the length and ± 0.5 mm for the height. The second probe could size EDM notches within an accuracy of about ± 0.6 mm for the length and ± 0.2 mm for the height. The summary of detection and sizing capability for technique #1 and #2 are presented in Table 3 and 4.
Technique #1 summary of UT detection and sizing capability.
|UT results||Probe # 1||Probe #2|
|Detection capability||2 x 0.5 mm up to 30 mm |
3 x 1 mm up to 80 mm
6 x 2 mm up to 90 mm
|3 x 1 mm from 5 mm up to 20 mm|
|Sizing capability||3 x 1 mm with (L = + 0.5 mm|
(h = - 0.5 mm
|3 x 1 mm with (L = + 0.6 mm|
(h = + 0.2 mm
|S / N ratio||> 14 dB, with tip signals > 6 dB||> 20 mm, with tip signals > 10 dB|
Technique #2 summary of UT detection and sizing capability.
|UT results||Probe # 1||Probe #2|
|Detection capability||2 x 0.5 mm up to 65 mm - H2|
3 x 1 mm up to 85 mm - H3
6 x 2 mm up to 110 mm - H4
|2 x 1 mm from 5 mm up to 35 mm - H1|
3 x 1 mm up to 35 mm - H1
4 x 2 mm up to 65 mm - H2
|Sizing capability||2 x 1 mm with (L = +1 mm|
(h = + 0.5 mm
6 x 2 mm with (L = ( 0.3 mm
(h = + 0.5 mm
|3 x 1 mm with (L = + 0.8 mm|
(h = - 0.3 mm
|S / N ratio||> 30 dB, with tip signals > 12 dB||> 40 dB, with tip signals > 16 dB|
The UT data for height measurement using probe # 1 (technique #1 and #2) are presented in Figure 6. The length accuracy for the same set-up is presented in Figure 7 and Figure 8.
The UT results with probe #2 were focused on 3x1 mm EDM notch. They are presented in Figure 9, for the height, and in Figure 10 for the length.
Figure 6 : Height accuracy for probe #1 - technique 1 and 2
Figure 7 : Length accuracy for probe #1 - technique 1 and 2 - short EDM notches.
Figure 8 : Length accuracy for probe #1 - technique 1 and 2 - long EDM notches.
Figure 9 : Accuracy in height sizing for probe #2 - technique 2.
Figure 10 : Length accuracy for probe #2 - 3 x 1 mm EDM notch - technique #2.
Figure 11 : Sectorial scan used for sizing an EDM notch on platform.
The results for technique #3 using the first probe concluded that detection is feasible up to hook #3. Sizing was performed in sectorial scan and B-scan. The accuracy for length evaluation is based on encoder positioning (± 1 mm ).The height was measured based on tip diffracted signals, and the actual angle for tip and corner. Its accuracy is about -0.5 mm. An example is illustrated in Figure 11.
Part 2 of feasibility study will investigate the detection and sizing for deeper range (75 - 200 mm), as well as optimization of technique #1 for the first 100 mm from the inlet / outlet face.
Acknowledgements: : the authors wish to thank Darlington Nuclear Power Plant - Power Train Engineering (Dave Bruce and Dale Craig), and Nuclear Technology Services Division for their support and granting the publication of this paper.
For more information see backup issue: NDTnet 12/97: NDT in Power Generation.