CURRENT UNDERSTANDING OF MICROBIOLOGICALLY INFLUENCED CORROSION Dr Margarita Vargas Mechanical and Corrosion Engineer Neptune Asset Integrity Services

Presentation Outline

Microbiologically Influenced Corrosion (MIC) Background

Current Developments on MIC

Case Study 1:

MIC of Duplex Stainless Steels

Case Study 2:

MIC studies at Darwin Harbour

Final Remarks/Recommendations

Questions

2

3

BACKGROUND

ANODIC AREA CATHODIC AREA CATHODIC AREA

e- e-

Microbial Colony

M2+

OH-

O2

M

Water - Microbial metabolism

(acids, sulphides, etc)

- Depolarization effect

(acceleration of

corrosion reactions)

- Effect of biofilm

formation

(ennoblement or

activation of metal

surface) AERATION ZONE created by a microbial colony. Metallic cations (M2+) are released from the anodic area resulting

in corrosion

Biofilm Formation

4

Exopolymeric substances (EPS)

Relevance of Microbiologically Influence Corrosion (MIC)

Estimated cost of MIC in Australia: > AU$10 billion in 2016

Microbes major players in Corrosion related failures in:

- Oil Fields (Prudhoe Bay Oil spill, 2006)

- Off shore Drilling Platforms (Failures of Duplex Stainless Steels)

- Pipelines (On-shore gas internal corrosion)

- Nuclear and Fuel Power plants

- Gas Coolers

- Water Supply Systems

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6

Material Substrate Microbial

Environment Inspection Methods

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Material Substrate Microbial

Environment Inspection Methods

Stainless Steels Marine Aerobic or Anaerobic

Potentiodynamic Polarisation Free Corrosion potentials

Electrochemical Impedance Spectroscopy (EIS)

Duplex SS Marine Anaerobic

(Sulphate Reducing Bacteria SRB)

Electrochemical tests

X-Ray Photoelectron Spectroscopy (XPS)

Aluminium

(e.g. 2024

Fungus

(Aspergillus Niger)

Pitting Corrosion

Biofilm Thickness

Fuels (e.g Biodiesel) Fungus (Moniliella wahieum) Chemical Analysis

Concrete Sulfur-oxidizing bacteria (SOB)

(A. thiooxidans, A ferroxidans)

Microbial analysis

Biofilm Thickness

Other MIC studies…

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Effect of flow rates (e.g. marine/tidal vs stagnant conditions)

Effect of Climate Change

Effect of Cathodic Protection

Effect corrosion inhibitors and coatings

Corrosion inhibiting capacity of bacteria or other microorganisms

Corrosion Under Insulation

Developing of MIC resistant Coatings

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CASE STUDY 1 Sulphate Reducing Bacteria-Duplex Stainless Steels

SRB culture Desulfovibrio salexigens

SRB cause 50% of all instances of MIC

(anaerobic corrosion)

SRB metabolism,

Metabolic reduction of sulphate to sulphide or hydrogen sulphide (H2S).

Anaerobic corrosion

mechanism:

4Fe + SO42- + 8H+ FeS + 3Fe2+ + 4H2O

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4 days 7 days 10 days

SEM

100m 100m

Optical Microscopy

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Post-corrosion characterization X-ray photoelectron spectroscopy (XPS) analysis

- Identification of Fe, Cr, Ni sulphides and oxides on metal surface.

- Formation of various types of sulphides: FeS, FeS2, Cr2S3, NiS

- Penetration of passive film, diminished passivity of metal.

1cm

1cm

0.5

cm

Base

metal

HAZ

Weld

metal

Epoxy

resin

1cm

1cm

0.5

cm

Base

metal

HAZ

Weld

metal

Epoxy

resin

Depassivation of Steels

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SRB environment

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.00E-09 1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02

i(A/cm^2)

V vs A

g/A

gC

lE(

Vo

lts

vs A

g/A

gCl)

Current density (Amp/cm2)

4th day

5th day 6th day

7th day

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.00E-09 1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02

I (Amp/cm^2)

E (m

V vs A

g/A

gC

l)

E(V

olt

s vs

Ag/

AgC

l)

Current density (Amp/cm2)

4th day

5th day

6th day

7th day

Abiotic environment

CASE STUDY 2 Corrosion studies in Darwin Harbour

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An understanding of the way in which the

local tropical marine environment of the

Darwin Harbour impacts corrosion of

structural materials.

This knowledge is beneficial to prevent and

remediate current corrosion issues impacting

assets in the Harbour.

Preliminary Research

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Corrosion behaviour of marine grade aluminium alloys and their weldments in natural seawater from Darwin Harbour

Set up of Corrosion tests in natural seawater at the

Aquaria at Australian Institute of Marine Science (AIMS)

MIG welded AA5083 specimens for total immersion tests (a) unpolished, (b) polished indicating WZ, HAZ

and BM

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Corrosion rate by weight loss

Corrosion rate of AA5083 and MIG welded AA5083 in unpolished and polished condition after immersion in natural seawater.

Corrosion rate at least 7 times higher than the reported in temperate environments

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Biofilm Identification by DNA Extraction

Preliminary identification of bacteria present by DNA sequencing

2

0

10

20

30

40

50

60

CP-1 CP-2 WP-1 CUP-1 CUP-2 WUP-1 WUP-2

Re

lati

ve a

bu

nd

ance

of

OTU

s (%

)

Sample

Neptuniibacter

Alphaproteobacteria

Desulfonatronum*

Thioprofundum or Thiohalomonas*

Gammaproteobacteria

Rhodobium*

Thioalkalivibrio*

Thiomicrospira

Left, Scanning electron micrograph (SEM) of corrosion product and biofilm formed on the surface of AA 5083 after 30 days of immersion. Right, DNA analysis result indicating the strong presence of biofilm after 30 days of immersion,

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Monitoring of the corrosion rates for long periods of exposure (i.e., measurement of corrosion potentials, weight loss and surface analysis).

In-situ Corrosion Darwin Harbour

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Research Station-Schematics

MIC Estimated Testing Schedule (5 years)

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Preliminary Planning

Collection of available field data and

navigation maps (location of buoys)

Integration of research program with Darwin Port

Maintenance Schedule

- Field recognition

- Estimation of sampling and testing

logistics

Identification of tidal zones and

environmental habitats

Material Selection and identification

Mooring chain material selection (based on DPC experience) ,

Consider design and weight

Procurement of materials supplies

(detailed in a separate schedule)

Characterization of material previous to

immersion (Chemical and microstructural)

Record of initial weight

Setting up of Research Stations

At locations consulted with DPC

and stakeholders

Monitoring/data collection required

Quarterly or Biannually

Corrosion visual inspection

Environmental monitoring

Microbiological testing

Wall thickness measurement

(corrosion rate )

Removal of material from

Research Station

Characterization of corrosion products

Record of final weight (weight loss-

corrosion rate measurement)

Interim annual and final report to

Stakeholders Test results with recommendations provided to stakeholders

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Final Remarks

Requirement of interdisciplinary collaboration for IMR of structures attacked by MIC

Different depassivation and corrosion attack mechanisms

Importance of including MIC management in overall Asset Integrity Programs