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