it was tmy seminar topic taken from a journal

1. In situ investigation of crevice corrosion on UNS
S32101 duplex stainless steel in sodium chloride
solution
Presented byPintu Kumar (13MT60R30)
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2. • Duplex stainless steels (DSSs) consist of ferrite phase
and austenite phase,
Properties it offers
• high strength and
• resistance to localized corrosion
lean DSS with lower nickel contents, have attracted a lot
of attention for its reduced resistance to such form of
corrosion.
• DSS 2101 (UNS S32101) is such a grade of lean DSS
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3. The aim of experiment
• To investigate the mechanism of crevice corrosion
on UNS S32101 duplex stainless steel in a
spontaneous passive system
• To provide a better understanding of the diversity of
crevice corrosion morphology
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4. critical crevice solution mechanism
• Induction period of crevice corrosion
• Accumulation of aggressive ions within crevice
• Subsequent de passivation and active dissolution of
base metal within crevice
• Migration of chloride and hyroxyl ions into crevice
• depletion of oxygen in the crevice and separation of
anodic and cathodic reactions

5. According to CCS theory
• The most severely attacked area-deepest regions of
the crevice.
• crevice corrosion can not go into propagation stage
directly to allow significant variation in crevice
solution composition.
Observations made, however, contradicted the CCS
theory
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6. IR mechanism
• It states, IR> ΔΦ criterion,for the onset of crevice
corrosion where I is the ionic current flowing out of
the crevice and R is the resistance of the crevice
electrolyte,
• ΔΦ is the difference between the applied potential
on crevice outer surface and the active/ passive
transition potential.
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7. Experimental
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8. experimental
• The specimens -commercial UNS S32101 duplex
stainless steel plates
• The chemical composition
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9. experimental
• plates as specimens were solution annealed at 1050
C for 0.5 h followed by water quenching. Samples
were mounted in epoxy resin to expose an area of 4
cm2 to serve as working electrode
• Prior to tests, the working electrodes were ground
with emery papers.
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10. • Followed by cleaning with acetone and methanol,
washed in double-distilled water and derided in air
thoroughly before use.
• The interfaces between the epoxy and sample were
sealed to prevent unwanted crevice corrosion
• then, allowing the system to react for 0.5 hr in 0.1 M
NaCl
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11. Fig. 1. Schematic diagram of the experimental setup
for the in situ observation of crevice corrosion
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12. Electrochemical measurement
• a potentiostat -To perform the Electrochemical
measurements
• platinum plate- counter electrode
• Saturated calomel electrode- reference electrode
• Cell arrangement is done to realize an artificial
crevice as shown before
• Electrolyte-0.1 M NaCl solun, 0.1M HCl+ 0.1M NaCl
• Applied potential- 0.1V, 0.3V, 0.5V
• Potentiodynamic polarisation curve-(-0.7 to 0.8V)
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13. Optical and SEM/EDX characterization
• scanning electron microscope- to investigate
microstructure and corrosion morphologies
• surface profiler- to find surface depth profile
• Camera-For recording the changes on the crevice
wall during crevice corrosion
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14. Results and discussion
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15. Potentiodynamic polarization curves
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16. Potentiodynamic polarization curves
• In acidic-chloride media,
As the crevice solution becomes more concentrated in
aggressive ions, the active peak becomes larger and
active/ passive transition potential increases and ΔΦ
decreases making IR> ΔΦ, as reqd for active dissolution
of base metal.
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17.  In 0.1 M NaCl with crevice
• corrosion potential lower-due to restricted area of crevice
hindering reduction of oxygen gas
• Higher passive current density-larger net anodic current
density
• Passive region-current density independent of potential
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18. Potentiostatic polarization to initiate crevice
corrosion
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19. Potentiostatic polarization to initiate crevice
corrosion
• At 0.1V(applied potential),
Cell current low, crevice corrosion in induction stage.
• At 0.3 V,
A delayed crevice corrosion (induction + propagation).
• At 0.5V,
Immediate crevice corrosion-Measured cell current
increased more rapidly than the one at 0.3V.
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20. In situ visual inspection of crevice corrosion
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21. In situ visual inspection of crevice corrosion
• During the early stage of crevice corrosion, the
corrosion products increase resistance of crevice
corrosion making IR> ΔΦ, reqd for onset of reaction
• Corrosion products on parts of the wall reduce active
current lowering local IR voltage turning part of the
crevice wall into passive state hence relocation of
active dissolution region occurs.
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22. Ex situ morphology analysis
Region-I
(centre
of the
crevice)
Boundary
Between II & III
Region-II
Severe
corrosion
Region-III
Ferrite phase
slightly etche
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23. A,C-most severe corrosion ( crevice mouth)
B- lightly corroded(centre of crevice)
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24. Fig. a- pot. Distribution on crevice wall
in the induction stage of delayed corrosion
Fig. b- Pot. Distribution in the propagation stage
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25. Induction stage
• As the aggressive ions accumulate in the crevice
solution, the passive films become unstable.
• The generated current fluxes result in large IR drop
with which the HER potential was reached in the
crevice.
• The evolution of H2 could further increase the
crevice solution resistance R.
• Consequently, a significant larger IR voltage is
produced by both larger current I and R that the IR >
ΔΦ criterion would be met. The induction stage ends
and propagation stage starts
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26. Propagation stage
• a net anodic polarization curve with active peak will
inhabit on the crevice wall.
• The crevice wall is subsequently attacked and the
corroded area expands towards crevice opening with
the moving passive/active boundary
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27. Conclusions
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28. Experimental results based on IR mechanism
1. Delayed and immediate crevice corrosion can be
initiated by potentiostatic polarization at EAPP = 0.30
VSCE and EAPP = 0.50 VSCE, respectively in neutral
0.1 mol/L NaCl solutions at room temperature.
2. The transition from induction stage to propagation
stage of the delayed crevice corrosion was explained
by IR mechanism with variation of the crevice
electrolyte composition.
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29. conclusion
3. Diversity of crevice corrosion morphology –due to
the relocation of active dissolution region on the
crevice wall that occured as a result of the effects
of corrosion products.
4. Reason for the immediate crevice corrosion -The
current fluxes caused by passive/active transition
of passive films on the crevice wall
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30. References
• Yang Y. Z., Jiang Y. M., Li J. , in situ investigation of
crevice corrosion on UNS S32101 duplex stainless
steel in sodium chloride solution, corrosion science
76 (2013) 163-169
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31. Thank you
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