V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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SIMULTANEOUS MEASUREMENT OF MATERIAL PROPERTIES AND THICKNESS OF CARBON STEEL

PLATES USING PULSED EDDY CURRENTS

V.O. de Haan1 and P. de Jong2

1 BonPhysics Research and Investigations BV, Putterhoek, The Netherlands; 2 Röntgen Technische Dienst bv, Rotterdam, The Netherlands

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Outline

• Introduction to RTD-INCOTEST©

• Principe of new method

• Measurements and results

• Discussion

• Conclusion

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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RTD-INCOTEST©

• Insulated COmponent TEST• Corrosion survey method • Ferrous objects covered with insulation, asbestos,

fire proofing, concrete or coating• INCOTEST is aimed at the detection of larger area

(not localised) corrosion• Pulsed eddy current technology

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Pulsed Eddy Currents

l

d

I

object

Transmitter coil

Receivercoil

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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0.001

0.01

0.1

1

10

100

0.01 0.1 1x

(x

)

1/3

-3 dB point

inverse power law t -1.5

exponential decay

Pulsed Eddy Currents / ,,)( 5.1 tΘlAtU

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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RTD-INCOTEST©

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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RTD-INCOTEST©

Typical applications

insulated vessels, storage tanks, piplines

riser/caisson (splash zone) inspection

rough corroded or coated surfaces

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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RTD-INCOTEST©

Advantages:

measurement at a distance

no cleaning needed

fast

Disadvantages:

reference needed

large footprint

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Principe of new method

= permeability

= conductivity

l = lift-off

d = thickness object

t = time

F = depends on geometry of probe

/ ,,,,)( 5.1 tΘtdlFtU

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Principe of new method

probe

tlA

tdlF

1

,,,,,,

2),( dlprobe 2 d

/ ,,,,)( 5.1 tΘtdlFtU

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Pulsed Eddy Currents tdlFtΘtU ,,,,/)( 5.1

0.001

0.01

0.1

1

10

100

0.01 0.1 1x

(x

)F

F < 1

F = 1

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Dimensions of probert2

rr2

rr1

rt1Transmitting coilnt turns

Receiving coilnr turns

lt1 lt2lr2lr1

Conducting plated

l1 / mm l2 / mm r1 / mm r2 / mm nTransmitter 2.15 7.05 5.25 7.70 400Receiver 2.15 7.05 7.70 10.25 1280

7.6 mm

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Measurement example

1E-6

1E-5

1E-4

1E-3

1E-2

0.001 0.01 0.1Time (s)

Ind

uct

ion

vol

tage

(V

) . 10-2

10-3

10-4

10-5

10-6

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Resultsobject

ms/mm2d

mmdfit

mmerror

%2

%

mm

D2 0.78 18.8712.976.87

19.813.57.5

6.43.8

21.0

0.80.70.2

5.04.49.3

0.90.60.6

A3 2.01 19.1213.237.09

21.114.19.6

9.94.64.9

0.70.81.1

10.56.2

36.0

2.00.82.6

A4 1.32 18.7713.156.99

18.915.010.4

47.016.0

9.8

2.41.60.3

0.914.148.4

0.21.93.4

D36 1.09 18.5312.766.85

20.313.07.5

4.04.18.5

0.20.91.4

9.62.29.5

1.80.30.7

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Discussion

• Only for the smallest thickness a deviation occurs larger than 2 mm. With the old model and a (not) favorable reference measurement the relative deviation would be at least (60) 30 %.

• As 2 varies around 1 the fit error is not determined by systematic differences but by the accuracy of the measurements.

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Discussion

• 1% of the signal is generated by eddy currents at a distance larger than 7 cm from the center of the coils. The plates dimensions were 16.5 by 16.5 cm, hence the footprint was a little larger than the object.

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Discussion

• The smaller the wall thickness of the object, the less accurate the fitted wall thickness. This is due to the special form of function F and is a limitation of the method.

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Conclusions

1 Simultaneous fit of two time constants from the signal measured by RTD-INCOTEST© pulsed eddy current method facilitates the determination of both material properties () and absolute thickness of an object.

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Conclusions

2 Measurements show that accurate geometry is very important. The object must be larger than the (effective) footprint and the distance between probe and object must be accurately known or measured.

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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Conclusions

3 Accuracy of 10% is possible and can be reduced by enhancement of probe design and measurement accuracy. Further research is needed to increase the accuracy of the method.

V1.0; May 27, 2004 16th WCNDT, Aug 30 - Sep 3, 2004 Montreal

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SIMULTANEOUS MEASUREMENT OF MATERIAL PROPERTIES AND THICKNESS OF CARBON STEEL

PLATES USING PULSED EDDY CURRENTS

Thank you for your attention