Evolution of NDE Techniques for Hydrodynamic Flaws in Darlington NGS Steam Generator Tubes

June 20, 2012

4th International CA

ND

U In-service Inspection W

orkshop and ND

T in C

anada 2012 Conference, 2012 June 18-21, T

oronto, Ontario

4th International CANDU In-service Inspection Workshop and NDT in Canada 2012 Conference, 2012 June 18-21, Toronto, Ontario

Evolution of NDE Techniques for Hydrodynamic Flaws in Darlington NGS

Steam Generator Tubes

by

S. Sullivan, G. Bruce, R. Mousavi, E. Cartar – OPG

Fourth International CANDU In-Service Inspection and NDT in Canada 2012 Conference – June 18-21, 2012

Outline of Presentation

• Darlington Steam Generators

• Tube Inspection Technologies deployed in OPG Steam Generators

• Development of ET (X-Probe) depth-sizing calibration curve

• Comparison of ET depth estimates with UT measurements and Destructive Examination

• Detection Capability POD curves for ET

• Summary3

Darlington NGS Steam Generators

� 4663 Incoloy 800 Tubes

� Eleven 410 Stainless Steel Lattice Bar Support Structures (“Egg Crates”)

� Eight 410 Stainless Steel U-Bend Anti-Vibration Fan Bar structures (AVBs)

� U-Bend Auxiliary AVB Retrofit Structures (have significantly reduced tube fretting)

� Preheater Section with Eleven 410 Stainless Steel Drill-Hole (Baffle) Plates

4

Support Plates in DNGS SGs

5

Lattice Bar Structures for straight-leg

tube sections

Drill-hole Baffle plates used in preheater

section – Baffle plates are windowed

Windows in Darlington PH Baffle Plates

6

Tube Inspection Technologies Deployed by OPG

• Basic – Zetec Bobbin Eddy Current Testing (ET) Probe

• Enhanced – Zetec 3x12 X-Probe Eddy Current Array

• High Resolution Characterization – Kinectrics Tiny Rotating Ultrasonic Tube Inspection Equipment (TRUSTIE)

- Normal Beam

- Axial Shear Wave

- Circumferential Shear Wave

7

8

Bobbin Eddy Current Probe

• Advantages: Inexpensive, Fast Scanning

• Disadvantages: Limited Sensitivity at Expansions and Support Plates, Insensitive to Circumferential Cracks, Limited Resolution for Flaw Characterization

X-Probe Eddy Current Array

9 Coil Layout for X-Probe Array for Darlington/CANDU 600 SG Tubes

24 Axial T/R pairs use

end row coils.

12 Circumferential T/R

pairs are pairs within the

same row.

Coil Layout

End Bracelet Coilsare Axial T/R Pairs

Center Bracelet Coils are Circumferential T/R Pairs

X-Probe Signals

Signals from Volumetric Flaw at PH Baffle Plate Location10

X-Probe Signals

11 Signal from a 15% tw Volumetric Flaw at PH Baffle Plate

Ultrasonic Testing of SG Tubes

12

Kinectrics Tiny Rotating Ultrasonic Tube Inspection Equipment (TRUSTIE)

N o rm a l B e a m

S h e a r fo r A x ia l F la w s S h e a r fo r C irc F la w s

TRUSTIE Signals (Normal-Beam Scans)

13• UT C-Scan displays of OD indications at PH support plate

locations showing various stages of degradation morphology

Baffle

Plate

Baffle

Plate

Removed Tube R3 C51 from D1 SG4 (2008)

14

• UT Measured flaw shape confirmed by DE. Maximum Flaw Depth by DE = 43% tw.

UT C-Scan Image

Photograph of Flaw at P05

SP Location

Summary of Significant Changes in NDE Addressing these Flaws

• Initially X-Probe data screening was performed using raw data channels. Signals from support plates interfered with flaw signals making detection of shallow flaws difficult.

• The X-Probe Analysis method was modified in 2010 to make use of multi-frequency mix channels to reduce interference from support plate signals. This has improved sensitivity to these flaws.

• Increased number of flaws reported due to improved sensitivity can cause concerns.

• Signal comparisons with historical data using current analysis technique shows presence of flaws in the past that were not reported. This alleviates concerns regarding increased numbers of flaws reported in current outages as compared to the past.

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Development of ET (X-Probe) Depth-Sizing Technique

• Depth sizing technique for these flaws based on X-Probe signals has been developed.

• A comparison of ET (X-Probe) Signals with UT depth measurements was used to develop a depth-sizing calibration curve in 2010 based on signal amplitude.

• Using the same information, AECL developed a similar calibration curve under a COG R&D Project.

• The initial ET sizing curve was deployed in the fall 2010 (D1021) SG inspection in Darlington Unit 2 and the Spring 2011 (D1111) SG inspection in Darlington Unit 1.

• A comparison of the ET depth estimates with UT measurements indicated that the ET sizing technique was overly conservative.

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Development of ET (X-Probe) Depth-Sizing Technique

• A comparison of the UT flaw depth measurements in Darlington Unit 2 in 2007 and 2010 indicated that the 2007 measurements were overly conservative.

• A comparison of UT flaw depth measurements in the 2010 Darlington 2 inspection with destructive examination verified the validity of the 2010 UT measurements.

• The ET sizing curve was modified by optimizing ET signal measurements with UT measurements with 2007 UT measurements from Darlington 2 replaced with 2010 measurements.

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Initial ET Calibration Curve with Known UT Measurements in 2010

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0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7 8 9 10

UT

Me

asu

red

Fla

w D

ep

th (

% t

hro

ug

h-w

all

)

Channel 121 Vmx (Volts)

Data Points

OPG Initial Calibration Curve - ch 122

AECL/COG Calibration Curve

Initial Calibration Curve Compared with PH Flaw Signals to 2011

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30

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0 1 2 3 4 5 6 7 8 9 10

UT

Me

asu

red

Fla

w D

ep

th (

% t

hro

ug

h-w

all

)

Channel 121 Vmx (Volts)

Data Points

Calibration Curve - ch 121

Comparison of Calibration Curves and Currently Known Flaw Depths

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30

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0 1 2 3 4 5 6 7 8 9 10

UT

Me

asu

red

Fla

w D

ep

th (

% t

hro

ug

h-w

all

)

Channel 122 Vmx (Volts)

Data Points

Calibration Curve - ch 122

Old Calibration Curve

Sizing Accuracy with Current Calibration Curve and Data

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0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

X-P

rob

e D

ep

th E

stim

ate

(%

th

rou

gh

-wall

)

UT Depth Measurement (% through-wall)

Ideal Sizing Reference

Data Points

RMSD = 6% TW

R = 0.8

Sizing Accuracy in Recent D1231 ET Inspection

220

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40 45 50

ET

(X

-Pro

be

) D

ep

th E

stim

ate

(%

th

rou

gh

-wa

ll)

UT Depth Measurement (% through-wall)

Data from D1231

Ideal Sizing Reference

Average Difference = +4% TW

RMSD = 7 % TW

Comparison of Destructive Examination (DE) with NDE

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Year Unit SG Row Col Location DE Depth Field UT X-Probe - Initial Sizing X-Probe - Current Sizing

(% TW) (% TW) (% TW) (% TW)

2008 1 4 3 51 P06 8 7 NDD NDD

2008 1 4 3 51 P05 43 40 47 38

2009 3 1 3 61 P05 24 20 24 22

2010 2 2 1 49 P05 21 18 19 18

2010 2 2 1 49 P07 47 46 52 42

2010 2 2 1 49 P09 35 34 59 47

Probability of Detection Based on Analyst Hits and Misses

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0.1

0.2

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0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

PO

D

Flaw Depth [% through-wall]

Darlington X-Probe & Bobbin Preheater Volumetric Flaws POD

X-Probe Bobbin X-Probe POD Bobbin POD

Bobbin &

X-Probe: 111

Data Points

Effect of Noise on PODEstimate Based on S/N Ratio > 2

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0.1

0.2

0.3

0.4

0.5

0.6

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0.8

0.9

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0 10 20 30 40 50 60 70 80 90 100

PO

D

Cavitation Flaw Depth [%tw]

DNGS X-Probe Preheater Cavitation Flaw Probability of Detection

(new proposed X-Probe sizing curve)

postulated POD, NDD locations postulated POD, semi-noisy locations

postulated POD, noisy locations Empirical X-Probe POD

Tubesheet Map Showing Tubes with all Preheater Volumetric Flaws

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Summary

• OPG’s Inspection Strategy now includes ET flaw sizingfor all Preheater Volumetric Flaws detected.

• Detection Capability of ET for these Flaws is being quantified and monitored as more data becomes available. Effects of background noise on POD has been evaluated.

• The TRUSTIE UT system continues to be deployed on targeted flaws to verify the ET measurements, bound the most significant flaws and monitor growth with the highest precision possible.

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