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Copy of Non Destructive Testing

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by

becker lorelei

on 18 December 2013

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Transcript of Copy of Non Destructive Testing

Eddy currents induce Joule effect which create overheating
Energy loss

Conductive materials only
Difficult for complex shape

Rapid attenuation of eddy currents (limit depth control)
No surface preparation
Absence of coupling

Speed control
No need for direct contact with the tested object
(can be performed through coatings)
Non Destructive Testing -
Eddy Currents

Summary
What are EDDY CURRENTS ?

Non Destructive Testing Principle for EDDY CURRENTS

Limiting phenomenon: the Skin Effect

Industry Applications


What are EDDY CURRENTS ?
Non Destructive Testing Principle for Eddy Currents
Limiting phenomenon : the Skin Effect
Industry Applications
Conclusion
Yannick Monferran
Thomas Guédot
Lorelei Becker
Adrien Piqué
Our Team !
Definition
Induced currents circulating in any mass of metal crossing by a magnetic field

LENTZ law:

Eddy Currents New magnetic field Opposed at the “master” field
Resulting Magnetic Field Varies in modulus and phase

Definition
Alternative Currents NON uniform distribution
The piece is
subjected to a magnetic field
through a coil (copper)
Each materials
have a
different impedance
We can
compare
different materials and find
properties
Advantages
Easy application
Quick diagnosis

Industrial control
Long metallic products (bar, tube...)
Tube with huge diameter
Aspect surface control
Control after surface thermal treatment
Measure of depth
Define materials
Different types of probes: differential & absolute
Absolute:
1 coil
Differential:
2 coils
Emission / Reception
Comparison
between 2 points of material

More
precise

Balance
between the both coils =>
decrease noises
Determination: length & width of the defect
Types of sensors
Limits
Needs
conductor materials

Surface defects

Difficulties for
complex shapes
Test example: instrumentation
Results visualization
Sensor
Piece
Lift-off
(air layer): must be constant for each measures => signal attenuation
How to determinate the depth of control ?
Frequency influences the depth of control
Alternative Current in the part
I

Variable Magnetic Field
H

Electric Field
Iw

Opposed in the center
In the same direction near the skin
Material influences the depth of control
Conductivity
Permeability
Skin Effect Applications
Superficial Defects Detection (with calibration)
Eddy Currents only in the skin
Others defects are not taken in consideration
Skin Effect Applications
Thickness Cover measure (with calibration)
Frequency Variation = Depth of Control Variation
Impedance Discordance between 2 measures
Different Materials

Alternating current
whose frequency may vary
The variation of impedance(=resistance) is measured
Control principle
Used to derminate a quenching efficiency
Definition
Experiment
Skirting coil


Internal coil


Planar sensor

Depends on:
Conductivity
Permeability
Defaults
These circulating eddies of current have inductance and thus induce magnetic fields



These fields can cause repulsive, attractive, propulsion, drag and heating effects

THANK YOU FOR YOUR ATTENTION
Different coils
Control principle
Control principle
Catherine BERAUD
Clare BOLAND

5 GM-IM
Groupe Production Energétique

Control principle
Electrical installation
Weatstone bridge
Detect
small changes
of
impedance

Control principle
Test
Results
Without defect
Defect
Full transcript