Simulation of eddy current nondestructive testing problems ... · PDF fileSimulation of eddy...

7th National NDT Conference of the Hellenic Society of Non-

Destructive Testing

Athens 15-17 October 2010

Simulation of eddy current nondestructive

testing problems with the CIVA software

platform

A. Skarlatos, G. Pichenot, C. Reboud, D. Prémel and S. Mahaut

CEA LIST, France

http://www-civa.cea.fr

7th National NDT Conference of ΕΛΕΜΚΕ, 15-17 October 2010, Athens 2

Outline

• Activities of CEA LIST in the field of NDT

• ECT module presentation:

The Volume Integral Method (VIM) formulation

• Applications

• Steam generator tube inspection

• Inspection of riveted planar multilayered structures

• Simulation of realistic flaws

• Modelling of the tilt effect

• Reliability assessment of ECT procedures using simulation supported

Probability of Detection (POD) calculations

• New challenges in the ECT modelling and perspectives of the CIVA

platform development


Outline




• Applications










Activities of CEA LIST in the field of NDT

NDT Simulation

Development of the CIVA platform:

• UT, ECT, RX

• Signal processing

• Reconstruction

• Analysis tools

Instrumentation

• Development of adaptive flexible

probe arrays

• Study of new technologies

of detectors

Methods

• Examination of noisy materials

• Complex geometries Increase of

productivity,

• Defect characterization, Waste,

• Concrete, Material ageing, …

76 permanent positions

25 PhD students, Postdocs

Average age : 35


Outline




• Applications










The ECT module of the CIVA platform

• Semi-analytical models for ECT simulation

based on the Volume Integral approach

• User interface oriented toward ECT

applications: few numerical parameters

ECT configuration defined within CIVA

• Description of canonical geometries using

Green dyads

• Series of fast calculations for parametric

studies

Variation plots

• Modelling of various types of coils and flaw

configurations


Principle of ECT modeling with the Volume Integral Method: 3 steps

W

E0

Primary electric calculated

in the unflawed W zone

W

Calculation of the total

electric field E in W

Description of the interaction between

the flaw and E0 using Green dyads:

E

The Volume Integral Method (VIM)

W

Calculation of

the probe response

(reciprocity theorem)

E0

E


Outline




• Applications










SG Tube Inspection in PWR

• Internal inspection using axial and

rotating coils in (helicoidal scan)

• Inspection of the tube bundles

between and near Tubes Support

Plates (TSP)

• Small tube diameters (~20 mm)

• Inspection of large distances along

the tubes


• Calibration based on the signal of 1 mm

through-hole

• Inspection of a transversal through-notch of

0.13 mm opening and 82° angular extension

Simul : 0.301 V / -17.4°

Exp : 0.3033 V / -18.5°

Real [dU]

Imag

[dU

]

Real [dU]

Imag

[dU

]

Simul : 0.2905 V / 151°

Exp : 0.2907 V / 148.8°

f = 100 kHz f = 500 kHz

Tube internal inspection using bobbin coils

(two identical bobbin coils connected in differential mode)

SG Tube Inspection in PWR


SG Tube Inspection near Tube Support Plates

Primary field calculation for the

tube + TSP structure (FEM)

Flaw interaction in tube without the

TSP (VIM)

Probe response with FEM primary

field + VIM flaw interaction

• Need for simulation of TSP of complex

shapes (trifoliate and quadrifoliate)

usually employed in commercial PWR

facilities

• Complete FEM simulations are

computational demanding

Use of a combined FEM-VIM approach


Validation for 3D notches

Experimental Data

Simulation

Inspection Frequency: 240 KHz

• External Longitudinal Notch

Thickness = 54%, Height = 10mm

SP

• Circumferential Through-Notch

Height = 0.113mm, opening = 82°

SP

Support plate characteristics

Thickness: 30 mm

Outer diameter: 40 mm

Material: Inox 304L: σ = 1.4 MS/m, μr = 1


• Remote field eddy-current (RFEC) technique

Ele

ctr

ic fie

ld (

Am

p.)

Near Field Remote Field Trans.

Zone

Phase

Inspection of ferromagnetic tubes

Fast neutron reactor

condensers

Tube manufacturing (metallurgy)

Petrochemical industry


E

R1 R2

Remote field inspection of a 50% external groove

Extension of the VIM formulation to take into account the variation of

the magnetic permeability

Inspection of ferromagnetic tubes

A. Skarlatos et al., IEEE Tans. on Magn., vol. 44, pp. 623-632, 2008


Inspection of riveted structures

Fatigue damage of riveted structures

• Multiple cracks initiating at rivets location

• Defects buried in different layers of the structure

• Flaws signals small compared to rivets signals

Corrosion of aircraft structures

Exposed Under paint • Galvanic Corrosion (contact between

dissimilar metals)

• Intergranular Corrosion (aluminum alloys

and stainless steels)

• Filliform Corrosion (deterioration under

organic coating)

Rivet

Layered structure

Aircraft corrosion J. E. Stump, http://www.asnt.org/

FAA report: Destructive Evaluation and

Extended Fatigue Testing of Retired Transport

Aircraft (DOT/FAA/AR-07/22,V1)


Excitation fields

in the workpiece

Green dyads calculated analytically

• Introduction of 2 finite zones in the stratified

medium containing the rivet and the flaw

2 layers

(conductivities s1

and s2, magnetic

permeability m0)

s1 , m0

s2 , m0 E2

E1

• System of integral equations for electric fields E1 and E2 (non magnetic case)

ECT of flaw located

at the bottom of a rivet

VIM modelling of riveted multilayered structures


Real part (mV) Imaginary part (mV) Real part (mV) Imaginary part (mV)

Flaw detection between two rivets

C. Reboud et al., Electromagnetic Non-Destructive Evaluation (XIII), IOS Press, 2009, pp. 129-136.

E2

E1 E3

E5

E4


Simulation of multiple interacting flaws

Transmitter

Receiver

Probe

scan

Perturbations of ECT signals

due to additional flaws

x

y

Amplitude of the ECT signal (mV)

Flaw signature

recovered by

a stronger one

Single coil

Probe scan

Simulation of ECT signals due

to flaws with complex shapes

x

y

Amplitude of the ECT signal (mV)

Better description

of realistic flaws

VIM matrix formulation: Flaw 1

Flaw 2

Flaw 3


Effect of the probe tilt

10°

Loss of symmetry and signal amplitude

roughly divided by a factor 2

in the tilted case

Loss of symmetry

Frequency: 200 kHz

Plate: conductivity = 18 MS/m

thickness = 2 mm

Coil: inner and outer radii = 1 mm and 1.25 mm

height: 1 mm

Flaw: parallelepipedal notch,

LX = 5 mm, LY = 0.3 mm and LZ = 0.5 mm

Lift-off: 0.5 mm

Real part

(X c

hannel)

Imagin

ary

part

(Y c

hannel)

Symmetric signal C. Reboud, G. Pichenot, and T. Theodoulidis, Review of Progress in

Quantitative Nondestructive Evaluation, 2008, pp. 1915-1921.


Validation results: CIVA vs. experimental data

Impedance variation due to the flaw

Agreement between simulation and experiment better than

18% in amplitude and 3° in phase

• Inconel plate

s = 1 M.S/m,

mr = 1,

Thickness 1.55 mm

• Air-cored coil

Int./ext radii: 1 mm / 1.8 mm,

Height: 1.92 mm,

Nb of turns: 360

lift-off: 0.155 mm (constant)

Frequency: 100 kHz

• EDM notch

Surface-breaking

Length 7 mm,

Opening 0.1 mm,

Depth 1.24 mm (80 %)

Effect of the probe tilt


• Propagation of uncertainties with the semi-analytical model

N lift-off values generated

with a normal distribution

N simulations N results

Extraction of some

characteristic value

from each result

• Introduction of statistical tools describing uncertainties

Variation of the probe lift-off

Description with a normal

distribution of values

Nominal value of the lift-off

Available distributions:

uniform, normal, log-normal, exponential, Rayleigh

Reliability assessment of ECT procedures

Simulation based POD calculations

in an ECT case


• Parametric model of

Probability of Detection (POD):

Signal Response

Berens, A.P. (1988), “NDE Reliability Data Analysis”, ASM Metals

Handbook, Volume 17, 9th Edition: Nondestructive Evaluation and

Quality Control, ASM International, Materials Park, Ohio, 1988, pp.

689-701

Definition of a detection threshold

F(z): normal cumulative distribution function

Parametric form:

m and s estimated from calculated points Lower bound

confidence interval

Characteristic value: here the flaw height

Reliability assessment of ECT procedures

• Example: Behavior with respect to

the flaw height, given some

description of lift-off variations

(bounded normal distribution)


Outline




• Applications










• Introduction of a contrast of permeability in planar configurations: Modeling

of magnetic fasteners and magnetic flaws

New challenges and development perspectives

• Modeling of thin cracks with complex shapes

• Simulation of other NDT methods: e.g. Magnetic Flux Leakage

• Modeling of new sensors (GMRs, EMAT, flexible sensors on Kapton film, etc.)

N

S N S N

S N S xJ

yB

zF

•8 •m

•m

100µ

m

Work under way:

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