Corrosion Testing's: OCP, LPR, and PD

1. Corrosion Engineering
Corrosion Testing's
Dr. Muhammad Ali Siddiqui
Assistant Professor
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Dr. MAS - NED UET Karachi - Pakistan

2. Content
1. Open Circuit Potential (OCP)
2. Linear Polarization Resistance (LPR)
3. Potentiodynamic Polarization Measurements
(PDMs)
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3. Corrosion Testing Equipment
• Electrochemical work station
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Working Electrode: the study material

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Open Circuit Potential (OCP)

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OCP Graphs

9. Linear Polarization Resistance
•Test Method, ASTM G-59 and G102
•Analysis of Test Data
•Polarization Resistance (Rp).
•Corrosion Rate Measurement
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Dr. MAS - NED UET Karachi - Pakistan

10. What is Linear polarization resistance?
• The polarization resistance (Rp) is defined as
the slope of a potential (E) (Y-axis) vs. Current
(I) (X-axis) plot in the vicinity of the corrosion
potential (Ecorr) or when the applied current is
nearing zero.
V = I R
V
I
Slop = R
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12. • LPR is used to determine
Rp  Icorr Corrosion Rate (CR)
ba = anodic Tafel
slope ~ 0.12
bc = cathodic Tafel
slope ~ 0.12
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13. In a general form,
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14. Experimental Procedure for
Polarization Resistance
Gamry Software 14
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Gamry Instrument Framework
What is Equiv. wt and from where we can get it?

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20. In vivo Experiment via LPR
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21. Potentiodynamic Polarization
Measurements
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ASTM G-3

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ASTM G-3

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Example -1

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Example -2: Active Passive Region

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Figure:
Potentiodynamic
polarization curves of
304 stainless steel in
0.5 M (Na 2 SO 4 þ H 2
SO 4 = NaOH)
solutions with various
Cl À concentrations at
room temperature. (a)
pH 1; (b) pH 4; (c) pH
7; (d) pH
DOI: 10.1080/00032719.2013.865201

29. What Information we can get from
PD?
Corrosion current density, Icorr
Corrosion Potentials, Ecorr
Corrosion Rate, CR
Pitting Potential, Ep
Passive region (if available)
Passive current density, ip etc.
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30. Thanks
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