Evaluation of pitting corrosion behavior of 316 l and 304 stainless steels exposed in industrial marine-urban environment field study

1. By
P. DHAIVEEGAN
EVALUATION OF PITTING CORROSION BEHAVIOR
OF 316L AND 304 STAINLESS STEELS EXPOSED IN
INDUSTRIAL-MARINE-URBAN ENVIRONMENT:
FIELD STUDY
Under the Guidance of
Dr. N. RAJENDRAN
Professor
Department of Chemistry
Anna University
Chennai-600025

2.  Global studies- Overall cost of corrosion loss is 4-5 % of GDP
 20-25 % of this cost could be avoided by using appropriate corrosion
control technology
 Atmospheric corrosion makes major contribution to this cost.
 The aggressiveness of the atmospheric constituents can be assessed –
measuring climatic & pollution factors or measuring corrosion rate of
exposed metals
 Factors Affecting the Atmospheric Corrosion
 Relative humidity (RH)
 Temperature (T)
 Sulfur content (SO2)
 Salinity (Chloride)
 Exposure time (t)
 Pollutants
Atmospheric Corrosion Strategy

3. Suffering Industries of Atmospheric Corrosion

4. Corrosion Failures on Infrastructure
A Concrete bridge failureA Concrete bridge failure
Corrosion Failure on bridgeCorrosion Failure on bridge
Corrosion in collapsed bridge at North CarolinaCorrosion in collapsed bridge at North Carolina
speedway (2000)speedway (2000)
4

5. Effect of ATM corrosion in Different Environments

6. Atmospheric Corrosion Studies in Chennai
 Atmospheric corrosion studies in India, have been
limited in number.
 From the above discussion we concluded that the
Atmospheric Corrosion is very high in Chennai compared
with other States.
 In Chennai most of these studies were aimed at
establishing pollution levels and none concentrated on the
marine environment.
 Deterioration of these materials along the coastal
regions of Chennai has been a major problem probably
due to marine atmosphere.

7.  In India, atmospheric corrosion data for 26 field exposure stations were
published (1970).
 The rate of corrosion was found to be vary from region to region.
 The intensity of attack was more in industrial area & along the seacoast.
 Corrosion map of India (Natesan et al.) indicated that the rate of corrosion
is spot specific and not region specific owing to insufficient data to
evaluate atmospheric corrosivity.
Atmospheric Corrosion Studies in India
Four Types Of Environments
(A) Humid–saline,
(B) Humid–saline–urban
(C) Humid–industrial And
(D) Plain Dry–urban Environments
Chennai is the zone where all the four above environments
namely coastal + urban +
industrial + plain dry pollutions exit.

8.  316L and 304 SS have caught the attention in modern technology in a wide
range of mechanical and corrosion resistant properties in the wide
atmosphere conditions.
 140 tons of 304 stainless steel was used as the construction material to build
a historic building of guildhall in London estimating it to have life span of
750 years
 It is generally accepted that high corrosion resistance of stainless steel due
to its passive film formation on its surface and it offers the protective
ability in the corrosive environments
 Over the decades, the Chennai City has emerged as an important Centre
for economical, historical, and cultural and trades development in the
State.
 This region includes thermal power plants, petrochemical plants, ennore
port, refineries, pharmaceuticals companies and residential buildings.
 Region is classified as marine-industrial-urban environment.
Introduction

9.  To understand the synergistic effect of chloride and sulfur dioxide in
corrosion rate of steels at in Industrial-Marine-Urban Environment were
studied in Chennai region.
 To determine the amount of corrosive agents viz., Cl-
, SO2 in the atmosphere
from wet candle and sulphation plate method.
 To study the surface morphology of the atmospheric corroded steels by
polarized optical microscopy (POM), atomic force microscopy (AFM) and
scanning electron microscopy equipped with energy dispersive X-ray
analysis (SEM-EDAX).
 To study the mechanical stability of the exposed samples by the Vickers
microhardness test
 To employ FT-Raman spectroscopy to investigate and to identify the
corrosion products which could not be obtained from XRD analysis.
 Corrosion behavior of exposed samples were monitored under open circuit
potential (OCP), electrochemical impedance spectroscopy (EIS),
potentiodynamic polarisation.
Objectives

10. Experimental Procedure
Exposure of specimenExposure of specimen
Specimen size - 100x50x3 cm
Exposure period - 3 Years
Exposure area - Industrial- Marine- Urban
Specimen size - 100x50x3 cm
Exposure period - 3 Years
Exposure area - Industrial- Marine- Urban
Exposure sitePower plantOil refineryUrban area

11. Characterization Techniques
Sulphation
plate
Wet candle
Sample exposure
Correct

12. Meteorological Corrosion Parameters
Figure 1 Average monthly values of (a) Temperature, (b) Relative humidity
(RH), (c) Rain fall, (d) Wind speed in industrial-marine-urban environment.
January
February
M
arch
April
M
ay
June
July
August
Septmber
October
November
December
-200
0
200
400
600
800
1000
RainFall/mm
January
February
M
arch
April
M
ay
June
July
August
Septmber
October
November
December
2
4
6
8
10
WindSpeed(kmph)
January
February
M
arch
April
M
ay
June
July
August
Septmber
October
November
December
75
80
85
90
95
RelativeHumidity(%)
Spring
Season
Summer
and Fall
Rainy
Spring
Season
Summer
and Fall
Rainy
Spring
Season
Summer
and Fall
Rainy
Spring
Season
Summer
and Fall
Rainy
January
February
March
April
May
June
July
August
Septmber
October
November
December
28
30
32
34
36
38
40
42
44
Temperature(°C)

13. Cl-
and SO2 Content in the IMU Atmosphere
January
February
M
arch
April
M
ay
June
July
August
Septmber
October
November
December
0
10
20
30
40
50
60
70
80
90
100
110
120
DepositionRate(mgm
-2
d
-1
)
A
Deposition of Chloride
Deposition of SO2
Figure 2 (a) Seasonal variations of Cl-
and SO2 obtained in the industrial-marine-urban
environment.
Spring Summer Rainy

14. 3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
0.000
0.001
0.002
0.003
0.004
0.005
CorrosionRate(mpy)
Exposue Time (Month)
316L SS
304 SS
Corrosion Rate of SS
Figure 3 Change of weight loss of 316L and 304 SS during the exposure in the industrial-
marine-urban environment.
Summer
and Fall
Rainy
Spring
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
0
5
10
15
20
25
30
35
40
45
50
WeightLoss(µg/cm
2
)
Exposue Time (Month)
316L SS
304 SS
Summer
and Fall
Rainy
Spring

15. Surface Appearance of Atmospheric Exposed SS
316L SS
304 SS
3 Month 6 Month 9 Month 12 Month 24 Month 36 Month
Figure 4 Macroscopic images of surface appearance of the 316L and 304 SS specimens
exposed for 3 years at industrial-marine-urban environment.

16. Hardness Analysis
Bare
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
0
50
100
150
200
250
300Hardness(Hv)
Exposure (Month)
316L SS
304 SS
Figure 5 Evolution of surface hardness of 316L SS and 304 SS in the industrial-marine-
urban environment.
Month
316L SS
Hv
304 SS
Hv
Bare 245 235
3 Month 250 240
6 Month 236 238
9 Month 230 200
12 Month 210 194
24 Month 205 186
36 Month 200 171

17. XRD Analysis
20 40 60
ATM-EN-316LSS-3
ATM-EN-316LSS-6
ATM-EN-316LSS-9
ATM-EN-316LSS-12
2θ (degree)
Intensity(a.u)
Figure 6 XRD patterns of 316L SS during the atmospheric corrosion exposure.

18. Raman Analysis
Figure 7 Comparison of Raman spectra of (a) 316L and (b) 304 SS during
atmospheric corrosion process.
200 400 600 800 1000 1200
RamanIntensity(a.u)
Wavenumber (cm
-1
)
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
200 400 600 800 1000 1200
RamanIntensity(a.u)
Wavenumber (cm
-1
)
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
316L SS 304 SS

19. SEM Analysis
Figure 8 SEM images of 316L SS after atmospheric exposure in IMU environment
as a function of exposure durations.
3 Month 6 Month 9 Month
12 Month 24 Month 36 Month

20. SEM Analysis
36 Month
Figure 9 SEM images of 316L SS after atmospheric exposure in IMU environment
as a function of exposure durations.
3 Month 6 Month 9 Month
12 Month 24 Month

21. Pit Depth Analysis of 304 SS
3 Month 6 Month 9 Month
12 Month 24 Month 36 Month
Figure 10 SEM images of 316L SS after atmospheric exposure in IMU environment
as a function of exposure durations.

22. Pit Depth Analysis of 316L SS
Figure 11 SEM images of 316L SS after atmospheric exposure in IMU environment
as a function of exposure durations.
3 Month 6 Month 9 Month
12 Month 24 Month 36 Month

23. AFM Analysis
Figure 12AFM images of 316L SS after atmospheric exposure in IMU environment
as a function of exposure durations.
3 Month 6 Month 9 Month
12 Month 24 Month 36 Month

24. AFM Analysis
3 Month 6 Month 9 Month
12 Month 24 Month 36 Month
Figure 12AFM images of 316L SS after atmospheric exposure in IMU environment
as a function of exposure durations.
3 Month 6 Month 9 Month
12 Month 24 Month 36 Month

25. Schematic Diagram of Mechanism of Pitting Corrosion

26. Pit depth and Surface Roughness Analysis
3 Month 6 Month 9 Month 12 Month 24 Month 36 Month
10
20
30
40
50
60
70
80
PitDepth(µm)
Time (Month)
316L
304
Bare 3 Month 6 Month 9 Month12 Month24 Month36 Month
10
20
30
40
50
Roughness(nm) Time (Month)
316L
304
Figure 13 Pit depth and surface roughness of the exposed 316L and 304 SS after
the exposing in IMU environment.

27. XRFAnalysis
3 Month 6 Month 9 Month 12 Month 24 Month 36 Month
0
5
10
15
20
25
30
35
40
45
Amount(wt%)
Duration (Month)
Cl
S
Na
K
Mg
Cr
Figure 14 XRF analysis of elemental composition of exogenous particle deposited on
the SS surface after 3 years of atmospheric exposure

28. Potentiodynamic Polarization Curves
-0.9
-0.6
-0.3
0.0
0.3
0.6
0.9
1.2
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
log(i/A)
Potential/V
Bare
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
-0.9
-0.6
-0.3
0.0
0.3
0.6
0.9
1.2
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
Bare
3 Month
6 Month
9 Month
12 month
24 Month
36 Month
log(i/A)
Potential/V
Figure 15 Potentiodynamic polarization curves of SS in 3.5% NaCl solution before
and after 3 years of atmospheric exposure

29. EIS-Bode Plot Curves
Figure 16 EIS curves of SS in 3.5% NaCl solution before and after 3 years of
atmospheric exposure
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
0
-20
-40
-60
-80
Phase/deg
Freq/Hz
Bare
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
0
-20
-40
-60
-80
Phase/deg Freq/Hz

30. Bode Phase Angle Analysis
Figure 17 Bode phase angle curves of SS in 3.5% NaCl solution before and after 3
years of atmospheric exposure
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
1
10
2
10
3
10
4
10
5
10
6
Z/ohm
Freq/Hz
Bare
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
1
10
2
10
3
10
4
10
5
10
6 Bare
3 Month
6 Month
9 Month
12 Month
24 Month
36 Month
Z/ohm Freq/Hz

31. Equivalent Circuit Diagram
Cpass
Rct
Rs
(a)
w
Rs
Rct
Rct
Cpass
Cdl
(b)
SteelPassive FilmSolution
Figure 18 Equivalent circuits for fitting the EIS data. (a) is for bare SS:
(b) is for atmospheric corrosion exposed in IMU environment.

32.  High alloy steels viz., 316L and 304 were field exposed for the period of
3 years (2012-2015).
 Surface appearance through photographic images of macroscopic
morphology of the Exposed Stainless Steels confirms the localized corrosion
(pitting corrosion) processes has taken place with the noticeable pits.
 304 SS showed more weight loss and corrosion rates compare to 316L SS.
The corrosive behavior of SS was found to be maximum during the winter
season due to the moisture content of their water holding capacity ability
for higher time period.
 The XRF analysis gave the reliable quantitative information about the
elemental chemical composition of deposited Cl-
and SO2on the SS surface
after the exposure period in IMU environment. During the initial exposure
the XRF analysis does not showed the appreciable deposition of Cl- and SO2
on the both SS surface due to the low concentration on the steel surface.
Conclusions

33.  After 6 months of exposure the presence of high amount of corrosive agents
was detected in XRF studies along with drastic increases in the elemental
composition of Na, Ca, Si, K. During the rainy season remarkable amount
of N present in the both steel surface were confirmed.
 AFM analysis of exposed 316L SS surface areas confirms the presence
passive film formed of small and large grains with different sizes of large
grains. The measured roughness using AFM analysis was found to be 20 to
40 nm.
 The Raman spectra obtained is in proof of the corrosion processes and the
formation of corrosion products as described in Stratman model. The
formation of stable goethite and iron oxides were confirmed with the sharp
peaks obtained in Raman spectra. Also Raman spectra confirmed the
existence of Mixture of goethite in higher amounts and with lower
amount of super paramagnetic maghemite .
 Polarisation studies confirms the higher corrosion resistance through lower
passive current of 316L in comparison to 304 steel. The higher RP value in
EIS spectra confirms the good corrosion resistance nature of exposed