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Feasibility study of the characterization of planar defects in a circular weld with Total Focusing Method Souad BANNOUF, Sébastien LONNE, (EXTENE) Loïc DE ROUMILLY, Christophe GIBERT, (EDF CEDRE)
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Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Jul 30, 2020

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Page 1: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Feasibility study of the characterization of planar defects in a circular weld with

Total Focusing Method

Souad BANNOUF, Sébastien LONNE, (EXTENE)

Loïc DE ROUMILLY, Christophe GIBERT, (EDF CEDRE)

Page 2: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Summary

1. Context

2. Problematic

3. Experimental set-up

4. TFM imaging

5. Results in direct mode

i. On machined mock-up EDM notches

ii. On a piping sample with real fatigue crack

6. Results in corner echo mode

i. Profile reconstruction

ii. On machined mock-up with EDM notches

iii. Artifacts filtering

iv. On a piping sample with real fatigue crack

7. Conclusion

page 2

Page 3: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Context

Welded assemblies of the circuits of the Nuclear Power Generation Centers present various geometries.

Some geometries have limited access for probes on one side of the weld

Area coverage or characterization limitations

Objectives :

Investigate in a technological watch context the interest of the Total Focusing Method in these configurations

- Detection

- Characterization (volumic or planar defect)

- Artifact/defect discrimination

- Height sizing

page 3

Page 4: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Problematic Knowledge of the profile necessary for:

Reconstruction and interpretation of the results

page 4

Weld bead + slope

Artifacts Characterization problems

+ artifact / default discrimination

Optimization of control parameters and post-

processing options by CIVA simulation

Interest of the TFM?

Accessible part of the piping

notch

Inaccessible area

Page 5: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Experimental set-up

Specimens

Machined mock-up :

Ferritic steel

EDM notches ( from 1.5mm to 8mm height)

Piping sample:

Ferritic steel

Complex 3D geometry

Thermal fatigue crack close the weld bead

Probe/Acquisition system

Probe : 64 elements with 0,6mm pitch

Frequency: 5MHz

Acquisition System: MultiX from M2M

page 5

Page 6: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

TFM imaging: principle Step 1: FMC (Full Matrix capture) acquisition

S11(t)

Sij(t)

SNN(t)

● ● ●

● ● ●

ROI

t11

tij

tNN

A11

Aij

ANN

S

Step 2 : TFM imaging reconstruction

• A posteriori focusing by coherent summation of all received signals Sij(t) for all points P of the zone to be imaged.

Algorithm : Tij(P) time of flight calculation for all transmit/receive couples (i;j)

• 1 element for transmission, N elements for reception

• Acquisition of a NxN matrix

page 6

Page 7: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

page 7

Reconstruction modes

Direct path Indirect path

Corner echo path

• Suited for planar defects • Reconstruction along the entire length

Page 8: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Machined mock-up: Results in direct mode

Notch # Theoretical

height

LL simulated

height (mm)

LL expermental

height (mm)

1 3 3 3

2 1.5 1.5 1.4

page 8

Simulation Experiment

Probe’s aperture does not fully cover the area to be controlled

Detection and height dimensioning are possible. Good estimation of the height of the defect

Good agreement between simulation and experimental results

Notch

accessibility limit

3mm notch

1.5 mm notch

3mm notch

1.5 mm notch

Page 9: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Machined mock-up: characterization in direct mode

page 9

Do the echoes observed belong to a planar defect or an inclusion-type volume defect?

Diffraction echoes ?

Verification in direct mode by displacement the probe aperture

Break in the backwall echo

The break in the backwall echo associated with the diffraction echo indicates the presence of a breaking planar defect

Page 10: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Piping sample: characterization in direct mode

Experimental measurement on the cracked

coupon show that TFM allows detection and

characterization of a fatigue crack in direct mode

The measured height is equal to the actual height

of the crack ± 0.2 mm (height = 5mm)

page 10

Diffraction

Break in the backwall echo

Diffraction echoes

Experiment – crack outside the probe aperture

Experiment – crack below the probe aperture

Page 11: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Results in corner echo mode - profile

reconstruction

page 11

The knowledge of the backwall profile is necessary for accurate reconstruction of the TFM

image in corner echo mode

CIVA allows recontruction of specimen profile with TFM imaging

Provides good results when the probe/specimen coupling is good and when the geometry to be

reconstructed is 2D

Comparison of theoretical and reconstructed mock-up backwall profile

Page 12: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Machined mock-up: results with corner echo mode

page 12

Good agreement between simulation and experiment

Determination of the most relevant reconstruction mode by simulation LTdT

Good estimation of the notch height

-6 dB drop amplitude sizing: OK

Reconstruction artifact

notch

Reconstruction artifact

notch

Experiment

Simulation Simulation

Experiment

Reconstruction artifact

notch

Reconstruction artifact

notch

3mm notch 1.5 mm notch

Page 13: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Artifact filtering

page 13

With artifact filtering

Artifact filtering: • Option available since CIVA 2016 • Filters artifacts due to bad reconstruction of the backwall echo in corner echo mode reconstruction • Elimination of the paths without physical sense

2

)cos(1)2/(cos)( 2

f

Without articfact filtering

Page 14: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Piping sample: results in corner echo mode

page 14

Without artifact filtering

With artifact filtering Presence of an acoustic signature at the crack position Reconstruction less « clear » than the one from the EDM notch Complex geometry (twisted component) Coupling probe/specimen non-optimal Characterization is possible but trickier

Page 15: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

Conclusion

Implementation by simulation and experimental validation of an advanced methodology to detect and

characterize thermal fatigue cracks with CIVA

Good agreement between simulation and experiment

Detection :

- In LL mode

- Observation of the diffraction echo or rupture of the backwall echo

Characterization :

- In LL mode : observation of the top diffraction echo + rupture of the backwall echo

- In LTdT corner echo mode : reconstruction of the flaw on its entire height

page 15

Page 16: Feasibility study of the characterization of planar defects in a ...€¦ · TFM imaging 5. Results in direct mode i. On machined mock-up EDM notches ii. On a piping sample with real

page 16

Thank you for your attention