a pulsed eddy current probe for inspection of candu reactor … · 2014-06-17 · • probe...
TRANSCRIPT
A Pulsed Eddy Current Probe for Inspection of CANDU® Reactor
Steam Generator Tubes
J. Buck1,2, P. R. Underhill1, S. G. Mokros1,2, J. Morelli2, T. W. Krause1
V. Babbar1,3, B. Lepine3, J. Renaud3
1Department of Physics, Royal Military College of Canada, Kingston ON2Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston ON3Atomic Energy Canada Limited, Chalk River Laboratories, Chalk River ON
Outline
• Description of Pulsed Eddy Current (PEC) testing
• Explanation of Principal Components Analysis (PCA)
• Overview of experimental setup
• Results:
– Isolation of fret signals at SS410 simulated support plate
– Fret depth sizing for various SS410 support plate hole IDs
– Shift detection and hole ID sizing without frets
• Continuing work
Motivation
• In-service inspection of CANDU steam generator
ferromagnetic drilled plate and broach support
structures:
– Gap measurements to identify corrosion of support
structures in the presence of tube fretting
– Detection of magnetite fouling at support structure
locations
– Development of a robust analysis technique to be used
for inspections
Pulsed Eddy Current Testing• A drive coil is excited using a square voltage pulse
• Transient eddy currents are produced via Faraday’s
Law of electromagnetic induction:
• Magnetization of ferromagnetic support structures under
approach to constant field conditions amplifies induced eddy
current response
• Transient signals are measured using pickup coils and analysed to
determine condition of steam generator tubes and surrounding
support structures
0.5 ms Transient Response
Conventional and Pulsed Eddy
CurrentConventional EC Pulsed EC
Sinusoidal excitation Square pulse excitation
More generic probe designs Probe tailored for inspection
Sensitive to small liftoff variations Less sensitive to small liftoff variations
Insensitive at large liftoffs (>5 mm) Effective at large liftoff (~10-30 mm)
Challenged in the presence of ferromagnetic
materials
Large magnetization component to the
signal
Depth of penetration limited by skin depth
and coil dimensions
Greater depth of penetration (approach to
DC) and field lines extend deeper
Pickup Coil Response
• Minimal change in time-domain signal variation in the
presence of different tube conditions
-0,5
0
0,5
1
1,5
2
2,5
3
0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4
Vo
lta
ge
[V
]
Time [ms]
Tube
Fret
Collar
Principal Components Analysis• Statistical method of turning highly correlated data into a
set of linearly uncorrelated variables called principal
components
• Each principal component accounts for the maximum
possible variance in the original data under the constraint of
orthogonality
• The dimensionality of the data can be reduced to a few
principal components and associated scores, simplifying the
analysis while maintaining most if not all of the original
information
0
1
2
0 0.05 0.10 0.15 0.20
Experimental DataVector 1Vectors 1, 2 and 3
file: e:\research\nsercdata.epfile: e:\research\nsercdata.ep
Time [ms]
Voltage [V
]
-0.2
-0.1
0
0.1
0.2
0 0.05 0.10 0.15 0.20file: e:\research\nsercvectors.epfile: e:\research\nsercvectors.ep
S3
S1
S2
Time [ms]
Eig
en
ve
cto
rs [
V]
• Transient Signal Response rebuilt using orthogonal PCA Eigenvectors
PCA vs. Fourier Analysis
0,01
0,1
1
10
100
1000
0 50 100 150 200 250
Am
pli
tud
e
Frequency Component
FFT 0.65
FFT 0.87
FFT 1.11
FFT Tube
Fast Fourier Transform (FFT) of various signals
PCA vs. Fourier Analysis
0,01
0,1
1
10
100
1000
0 5 10 15 20 25 30 35 40 45 50
Am
pli
tud
e
Component
PCA 0.65
PCA 0.87
PCA 1.11
PCA Tube
FFT 0.65
FFT 0.87
FFT 1.11
FFT Tube
Fast Fourier Transform (FFT) of signals
PCA of signals
Probe Design• Probe designed by NDT group at RMCC
• Drive coil wound coaxially with the probe body
• Pickup coils are arranged in sets of 4 at 90° intervals both in front
and behind the drive coil
• All pickup coil axes are perpendicular to the axis of the drive coil
and probe body
Front
Experimental Apparatus
SS410 Collars (with IDs) for
simulating varying degrees
of corrosion in support
plate structure
Micrometer apparatus
Sample fretted Alloy-800 SG tube
18.0 mm 18.8 mm
20.3 mm 21.8 mm
Collar and Fret Signal Separation• Ferromagnetic collar appears in S1 with a FWHM of 26 mm in both experiments
• Shape characteristic of a fret appears here in S3 in both experiments
• S2 appears to combine effects seen in S1 and S3
• PCA provides separation of feature/flaw signals at ferromagnetic structures
Fret Depth Sizing• Frets can be identified at ferromagnetic support structures using
translational measurements as shown previously
• Frets were located at the SS410 collar, with the tube centered
within the collar using the micrometer apparatus
• Five different fret depths were examined in combination with
four different collar ID sizesFret
Number
Fret Depth
[mm]
1 0.65
2 0.74
3 0.87
4 1.00
5 1.11
Collar
Number
Collar ID
[mm]
2 18.0
3 18.8
4 20.3
5 21.8
Fret Depth Sizing• Fret depth can be related to S2 with a centered tube
• The S2 fret depth relation appears to be independent of collar ID,
which simulates uniform corrosion of the drilled supports
-0,8
-0,6
-0,4
-0,2
1E-15
0,2
0,4
0,6
0 0,2 0,4 0,6 0,8 1 1,2
S2
[A
rbit
rary
]
Fret Depth [mm]
Collar 2
Collar 3
Collar 4
Collar 5
Mean
Poly. (Mean)
Fret Depth Sizing• Finite Element modelling data generated using a COMSOL model underwent
PCA to be validated by experimental results
• After normalization model provides excellent quantitative agreement with
experiment for fret depth measurement using S2
y = 1,9346x2 - 0,5183x - 0,9301
R² = 0,9896
y = 1,9759x2 - 0,4114x - 1,0054
R² = 0,9902
-1,5
-1
-0,5
0
0,5
1
1,5
0 0,2 0,4 0,6 0,8 1 1,2
S2
[A
rbit
rary
]
Fret depth [mm]
COMSOL
Experiment
Poly. (COMSOL)
Poly. (Experiment)
Tube Shift and Collar ID Sizing• Probe centered within the SS410 collar
• Nominal Alloy-800 tube shifted horizontally from one
side of the collar to the other in 0.25 mm increments
• Four different collar sizes used to simulate different
amounts of support structure corrosion
Tube Shift and Collar ID Sizing• Peak voltages for the different shift positions within the
SS410 collar were combined differentially
• Offset at the centered position stems from coil imbalances
-0,4
-0,3
-0,2
-0,1
0
0,1
0,2
0,3
0,4
0 0,5 1 1,5 2 2,5 3
Dif
fere
nti
al
Vo
lta
ge
[V
]
Tube Shift [mm]
Diff 3-7
Diff 4-8
Poly. (Diff 3-7)
Poly. (Diff 4-8)
• S1 vs. S2 for the four different collar IDs
• S2 provides a measure of the tube shift from a centered
position while the distance between curves can be used to
determine collar ID
Tube Shift and Collar ID Sizing
27,00
27,50
28,00
28,50
29,00
29,50
-4,00 -3,00 -2,00 -1,00 0,00 1,00 2,00 3,00 4,00
Sco
re [
S1
]
Score [S2]
C5c37
C4c37
C3c37
C2c37
Poly. (C5c37)
Poly. (C4c37)
Poly. (C3c37)
Poly. (C2c37)
Tube Shift and Collar ID Sizing• The minimums of the S1 vs. S2 curves have been plotted against
collar ID data sets collected using two different coil pairs
• Suggests that using calibration vectors would allow for ID sizing
25
25,5
26
26,5
27
27,5
28
28,5
29
29,5
17 18 19 20 21 22 23
S1
Min
ima
[A
rbit
rary
]
Collar ID [mm]
C37
C48
Poly. (C37)
Poly. (C48)
Summary• A Pulsed Eddy Current Probe has been developed for evaluation
of ferromagnetic support structures in CANDU® steam generators
• Principal Components Analysis (PCA), applied to acquired
transient signals, demonstrates capability to separately measure
gap and position (shift) of SG tube, which can be used to evaluate
condition of surrounding support structure
• PCA also shows capability to separate out and quantify the effect
of SG tube frets on signals obtained at support structures
• PCA provides a robust and powerful statistical tool for flaw
detection and characterization of transient signals
Continuing and Future Work
• Combine tube shift, collar sizing and fret depth
measurements in a single experiment
• Validate the use of calibration vectors with “blind” tests
• Investigate the effects of probe eccentricity and non-ideal
alignment of pickup coils with flaws
• Investigate the effects of magnetite fouling of the tube ID
and OD on transient signal response
• Examine trefoil broach supports using newly designed probe
Questions?