acoustic emission testing for the detection of localized … · •history of corrosion detection...
TRANSCRIPT
Acoustic Emission Testing for the
Detection of Localized Corrosion of
Aluminum 2024 alloy in 3.5% NaCl
Miguel A. González Núñez
2014 Airlines for America Nondestructive Testing Forum
OUTLINE •Introduction
•History of Corrosion Detection with AE
•How can we Detect Corrosion with AE?
•Potential Sources of AE during Active Corrosion.
•AE Measurements in Controlled Corrosion Experiments
•Results
•Conclusions
•Future Work
Acoustic Emission
AE detects
GROWING defects
within the material
under loading and
ACTIVE damage
Real time method
AE System
AE : Stress Waves due to Sudden Movements in Materials
Introduction
AE Source Amplitude will be Governed by (a) Size, (b) Speed of Source Event
Scale of AE Source Processes
Introduction
Initial Corrosion experiments
Polarization scan/AE
AE Pitting Corrosion Detection Potentiodynamic scan/AE
0.01
0.1
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1000
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i co
rrm
A/c
m2
Ecorr mV vs. Ag/AgCl
Ecorr
AC
TIV
E
PA
SS
IVE
TR
AN
SP
AS
SIV
E
Pitting
1000 1500 2000 2500 3000 3500 4000 4500
0
10
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30
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80
0.01
0.1
1
10
100
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-1825 -1725 -1625 -1525 -1425 -1325 -1225 -1125 -1025 -925 -825 -725 -625 -525
Time (seconds)
Am
plitu
de (d
B)
i corr
mA
/cm
2
Ecorr mV vs. Ag/AgCl
Ecorr
AE Pitting Corrosion Detection
Potentiodynamic scan/AE
Corrosion Mechanism
Electrochemical corrosion occurs in two stages: •Anodic dissolution of the metal and, •Cathodic reduction of some species existing in the solution, •On the cathodic sites of a metal surface close to the anodic zone on a single, whole metal surface.
•ALL THE REACTIONS OCCUR ON THE SURFACE OF THE MATERIAL CORRODING.
Example of different AE sources
during Corrosion Monitoring
crack propagation
EMI Turbulence noise
Pitting H2 Evolution
Need of pattern
recognition analysis
=> Data base
AE Measurements in Controlled
Corrosion Experiments
CE RE
WE
Potentiostat AE System
AE
sensors Corrosion Cell
AE Rate – icorr vs. E Results
Preliminary Results
•During settlement of the corrosion cell and without any
external perturbation to the corrosion cell, AE signals
were easily detected with amplitudes above 40 dB.
•After settlement of the corrosion cell, a potential scan
was carried out to identify different corrosion regions on
Al alloy.
•Applied voltage and current were recorded, in order to
correlate with AE activity.
•AE signals were detected at specific region of the
polarization curve.
Preliminary Results
•AE signals related to cathodic reaction (water
decomposition).
•AE signals detected around Ecorr active region
related to oxidation of Aluminum.
•AE signal detected at transition knee from passive
to transpassive aluminum (breakdown of passive
oxide).
•We are able to locate areas where damage is
developing.
Future Work
•Electrochemical Noise experiments in order
to characterize the corrosion rates or
localization index at different potentials.
•Correlation of AE features with corrosion
rates.
Conclusions
1. Corrosion Can Be Detected with Acoustic Emission.
2. Good Agreement was Observed between the Corrosion
Activity and Acoustic Emission Activity as a function of NaCl
concentration.
3. Calculation of the Corrosion Rate and the AE Hit Rate,
Showed a Strong Correlation between these Two Parameters.
4. AE Provides a Non Intrusive way to Measure Corrosion
Activity.
5. Periodic Measurements at Regular Intervals will Allow to Take
Action to :
i. Stop or Mitigate the Deterioration due to Corrosion
ii. Identify the Triggering Condition
iii. Validation of Protective Schemes are Effective
