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Surface Microbiological Analysis
Biofouling and MIC of Coated Steel in Marine EnvironmentSamanbar Permeh1, Mayren Echeverria Boan1, Berrin Tansel1, Kingsley Lau1 and Matthew Duncan2
1.Civil and Environmental Eng Dept., Florida International University (FIU), 2. Florida Department of transportation
• Severe corrosion of submerged steel H-Piles in a Florida marine bridge.
• Corrosion suspected to be MIC related.
• Localized corrosion cells/pits of up to 3 inch in diameter.
• Well-aerated conditions due to significant tidal action.
• Microbiological and chemical analyses of water samples indicated :
• SRB, IRB, APB, SFB
• and sufficient nutrient levels for microbial growth.
Research Questions and Objectives
Can marine fouling sustain proliferation of bacteria associated with MIC?
• What kind of crevice environments can exist due to biofouling?
• Can biofouling-induced crevices support microbial growth related to MIC?
Can coatings be used to mitigate enhanced bacteria growth in fouling-induced crevices.
• Steel coupons placed at Florida bridge site associated with MIC.
• Commercially available polyurea and water based copper-free antifouling
coatings used.
• Three surface roughness conditions applied on polyurea samples
( as-cured, 400 grit and 60 grit)
• Microbiological analysis at ~60 , ~170 and ~300 days .
Biological Activity Reaction Test (BART) kits used to monitor the
population of MIC related bacteria (SRB, IRB, SLYM and APB)
• Laboratory electrochemical testing on decommissioned samples after
~170 and ~300 days.
• Corrosion measurement:
Open circuit potential (OCP). linear polarization resistance (LPR) ( 25 mV
at scan rate of 0.05 mV/s), and electrochemical impedance spectroscopy
(EIS) with 10 mV AC perturbation voltage and frequencies 1MHz > f >1Hz
Visual Inspection Introduction
• Barnacles can develop in the tidal region(esp.4-5 ft. BMG) but soft marine masses populated
with sedentary fauna developed at >4ft. BMG.
• Anti-fouling coatings mostly prevented marine growth throughout the ~300-days test period.
• Polyurea coating had significant marine growth and barnacle attachment after ~60 days.
• Barnacle size was thought to be related to depth, immersion time, nutrient availability and
shelter. Different crevice environments, (tight crevices under the carbonate plates and porous
crevices under fauna and flora of marine foulers) can form and enhance both microbiological
and localized corrosion activity.
•App. Ecorr (-600 to -700 mVSCE ) closer to Ecorr for uncoated samples and higher current for field
samples than lab control samples indicating possible interaction with steel interface (water
penetration/coating degradation).
•The multiple and thick applied layers of polyurea may in part account for non-representative and
non-ideal conditions that can lead to premature coating failure.
• Nyquist plots for both
coatings showed double
loops, which can be
associated not only with
dielectric characteristics
of the coating but also
metal/solution interfacial
behavior.
• Antifouling coating generally had less
surface bacteria population (low SRB
and IRB after ~170 and ~300 days)
indicating that biofilm and subsequent
fouling can still be reduced.
• Polyurea coating showed high levels of
bacteria and subsequent marine growth.
Bacteria population did not have clear
correlation to the roughness of polyurea
coated samples.
Conclusions• The water based copper-free anti-fouling coating showed relatively better antifouling performance,
prevented marine growth and had generally less surface bacteria population over the time of
exposure.
• The polyurea coating did not prevent marine growth from developing in any of the test conditions
and significant barnacle attachment was observed by the earliest days of exposure.
• Relatively smooth surface roughness could still allow for secure barnacle attachment but indication
of larger barncle plate sizes at rougher surfaces.
• The field observations show that different crevice environments due to the accretion of marine
growth can form and possibly enhance microbiological and corrosion activity.
Acknowledgments
This investigation was supported by the Florida Department of Transportation (FDOT). The
opinions, findings and conclusions expressed here are those of the authors and not necessarily
those of the FDOT or the U.S Department of Transportation. Support from the FDOT State Materials
Office is acknowledged here. The authors acknowledge the assistance by Harpreet Sidhar in the
coating application.
Electrochemical Measurements (EIS)
• Heavy marine growth such as barnacles, tunicates, and hydroids observed
on piles.
• Their presence could affect the corrosion process by creating differential
aeration cells, localized corrosion, and support biofilm.
• Biofoulers may promote localized environments with the development of
occluded spaces and crevices.
• The crevices have physical, chemical, and environmental conditions that
may promote microbially growth associated with MIC
In MIC, microorganisms influence the kinetics of the corrosion process by forming a biofilm that can:
• Create oxygen heterogeneities and increases mass transport resistance near a metal surface.
• Generate corrosive substances (such as an acid), and other substances that serve as cathodic
reactants.
• MIC often associated with
IRB, APB, SFB, and SRB. SRB often studied.:Possible corrosion mechanism by SRB4 Fe → 4 Fe+2 + 8 e-1 (anode reaction)8 H+1 + 8 e-1 → 8 H (cathode reaction) SO4
-2 +8H→ S-2 +4H2O (cathodic depolarization by SRB) 8 H2O → 8 OH-1 + 8 H+1 (dissociation of water)2 H+1 + S-2 → H2S (reversible reaction) Fe+2 + S-2 → FeS (anode corrosion product) Fe+2 + 6 (OH)-1 → 3 Fe(OH)2 (anode corrosion product)
• Uniform corrosion with moderate corrosion rate expected in
natural water systems, but localized corrosion due to MIC.
Cathodic depolarization observed in lab test solutions with SRB.
• Crevice environment can cause localized corrosion with
possible accumulation of aggressive chemical species and
acidification.
• Tight Crevice : Possible limitation of hydrogen gas formation
within tight crevices and oxygen depletion may cause limitation
on reduction reaction. It was postulated that lower availability of
ads hydrogen and less sulfate would reduce SRB activity. Lab
testing resulted in no cathodic depolarization in tight crevice
conditions inoculated with SRB.
• Porous Crevice: Acidification in crevice space and supported
hydrogen and oxygen reduction result in noble corrosion
potential . Cathodic ennoblement observed in conditions with
SRB in porous crevice conditions due to availability of ads
hydrogen and sufficient nutrient level .
Methodology
Fouling Induced Crevices
Pitting Corrosion on Submerged Steel PilesMax. Barnacle Plate Diameter on Coated Steel Coupons
Marine flora and sedentary fauna included barnacles, tunicates, hydroids, and sponges.
2 ft. Below The Marine
Growth Line
†Marine fouling on plain steel. ‡ Below marine growth (on concrete
footer).,*Marine flora on all Polyurea. ** Isolated oyster on Polyurea.
-800
-750
-700
-650
-600
-550
-500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Co
rro
sio
n P
ote
nti
al/
mV
SC
E
Time (Days)
De-aerated Condition
NO SRB
NO SRB HARD CREVICE
NO SRB SOFT CREVICE
SRB
SRB HARD CREVICE
SRB SOFT CREVICE
-800
-750
-700
-650
-600
-550
-500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Co
rro
sio
n P
ote
nti
al/
mV
SC
E
Time (Days)
Naturally Aerated ConditionNO SRB
NO SRB HARD CREVICE
NO SRB SOFT CREVICE
SRB
SRB HARD CREVICE
SRB SOFT CREVICE
~ 8 ft.~ 5 ft. ~ 6 ft. ~ 7 ft.
Antifouling Coating
Day 0
Da
y 1
70-3
00
Aft
er
Cle
an
ing
~ 2 ft. ~ 3 ft. ~ 4 ft.
Day 6
0
~ 5 ft.
~ 8 ft.~ 5 ft. ~ 6 ft. ~ 7 ft.
Polyurea with 60 Grit Surface Roughness
Day 0
Day 1
70-3
00
Aft
er
Cle
an
ing
~ 2 ft. ~ 3 ft. ~ 4 ft.
Day 6
0
~ 5 ft.
Polyurea with 400 Grit Surface Roughness
~6ft. ~ 7 ft. ~ 8 ft.
Day 0
Da
y1
70-3
00
Aft
er
Cle
an
ing
Da
y 6
0
~ 3 ft. ~ 4 ft. ~ 5 ft.
An
tifo
uli
ng
Co
ati
ng
Po
lyu
rea
Co
ati
ng
Po
lyu
rea
Co
ati
ng
wit
h 6
0 G
rit
Su
rfa
ce
Ro
ug
hn
es
s
Po
lyu
rea
Co
ati
ng
wit
h 4
00
Gri
t S
urf
ac
e R
ou
gh
ne
ss
Da
y 0
Day 1
70-
300
Aft
er
Cle
an
ing
Day 6
0
~ 6 ft. ~ 7 ft. ~ 8 ft.~ 3 ft. ~ 4 ft. ~ 5 ft.
Polyurea Coating
•Reference control samples had high
impedance values (1 to 3 orders of
magnitude larger than the field exposed
samples.
• Lower impedance measured (<500 ohm)
for all field samples, which implicate the
adverse effect of immersion and
macrofoulers growth on coating
durability.
SRB Population CFU.ml-1
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
As-Cured 400 Grit 60 Grit
Steel Antifouling Polyurea
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
As-Cured 400 Grit 60 Grit
Steel Antifouling Polyurea
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
IRB Population CFU.ml-1
APB Population CFU.ml-1
SFB Population CFU.ml-1
0.01
0.1
1
10
100
1000
10000
~2 f
t
~3 f
t
~4 f
t
~5 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~3 f
t
~4 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~3 f
t
~4 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~2 f
t
~3 f
t
~4 f
t
~5 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
As- Cured 400 Grit 60 Grit
Antifouling Polyurea
Co
rro
sio
n C
urr
en
t (µ
A)
Dash line show the range for new coatings in control laboratory test solution
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
~2 f
t
~3 f
t
~4 f
t
~5 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~3 f
t
~4 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~3 f
t
~4 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~2 f
t
~3 f
t
~4 f
t
~5 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
As-Cured 400 Grit 60 Grit
Antifouling Polyurea
To
tal Im
ped
en
ce (
oh
m)
At
1H
z
Dash line show the range
for new coatings in control
laboratory test solution
-900
-850
-800
-750
-700
-650
-600
-550
-500
-450
~2 f
t
~3 f
t
~4 f
t
~5 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~3 f
t
~4 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~3 f
t
~4 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
~2 f
t
~3 f
t
~4 f
t
~5 f
t
~5 f
t
~6 f
t
~7 f
t
~8 f
t
As-Cured 400 Grit 60 Grit
Antifouling Polyurea
Co
rro
sio
n P
ote
nti
al/m
VS
CE Dash line show the range
for new coatings in control
laboratory test solution
Range of field
measurements for
uncoated steel
Electrochemical Measurements (LPR)
Field Measurements at ~170 and ~300 days
0
100
200
300
400
500
0 100 200 300 400 500
-Z'' (
Oh
m)
Z' (Ohm)
~8 ft
~4 ft
Control Sample
0
10
20
30
40
50
0 10 20 30 40 50
-Z'' (
Oh
m)
Z' (Ohm)
39.9 kHz
1Hz
1MHz0
10
20
30
40
0 10 20 30 40 50 60 70 80
-Z'' (
Oh
m)
Z' (Ohm)
As-Cured ~4 ft 400 Grit ~ 4 ft
60 Grit ~ 4 ft As Cured ~8 ft
400 Grit ~ 8 ft 60 Grit ~ 8 ft
Control Sample
0
1
2
2 3 4 5 6 7 8 9 10
-Z'' (
Oh
m)
Z' (Ohm)
1Hz
1Hz1Hz
1MHz
397Hz
Antifouling Coating
Red Line indicate boundary for the aggressive condition
MIC Mechanism and Role of Crevices
The evidence support importance of early presence of bacteria growth to allow fouling formation,
however marine growth can provide aggressive conditions to support microbe development and MIC.
Further research is ongoing to elucidate the contribution of different type of crevices to enhance MIC.
Water
Submergence
Line
0.25”ф
2”ф
0.5*0.5 ф
3.5 “ф
1“ф