microbial influenced corrosion (mic) in maritime...
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Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
April 1, 2019, 2nd international symposium on corrosion and fouling, Antwerp, Belgium
Dr. Job Klijnstra +31 (0)6 10 49 00 59Fouling control & material protection [email protected]
Dr. Nanni Noël-Hermes +31 (0)6 46 84 72 96MIC and biofilms [email protected]
Microbial influenced corrosion (MIC) in maritime environment
Corrosion, Failure analysis and Antifouling research since 1964
Former corrosion laboratory Royal Netherlands Navy
Expertise
Corrosion
Electrochemistry
Metallurgy
Antifouling
Microbiology
Coating performance testing
Material durability in seawater
Natural seawater
Outdoor exposure
In-house laboratory of Royal Netherlands Navy
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ENDURANCE through RESEARCH
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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Microbial influenced corrosion
MIC is a rapid form of corrosion initiated or accelerated by microorganisms
Localized form of corrosion
Direct or indirect mechanism
Up to 20% of all serious corrosion events are related to MIC
It affects a wide diversity of industries such as maritime & offshore, water distribution and waste water treatment systems, oil and gas, food industry
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General facts about microorganisms:
Characteristics of microorganisms related to MIC: (Borenstein, 1994)
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
Microorganisms (MO’s) interact with surfaces and form a biofilm:
(a) = cells attach to the surface biofilm formation
(b) = aerobic and anaerobic zones are formed MO’s create their own (micro) environment
(c) = ions are trapped, localized chemical and physical gradients are created at the metal surface dissolving of the metal and pit formation
Biofilms, critical factor for MIC
Preferred sites for attachment are (micro-) scratches, cracks, crevices, etc.
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MIC - complex processes
Uptake of nutrients out of liquid or soil, conversion to
acids and other corrosive by-products such as CH4, H2S,
etc.
Change of local environmental conditions
acceleration of corrosion processes
resulting in pitting, cracking and other forms of corrosion damage
Damage of materials such as metals, concrete or polymers is possible!
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Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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MIC in maritime environment
Types of corrosion
Severe corrosion
splash zone
Tidal zone
Accelerated low water
corrosion (ALWC)
Localized corrosion
under clusters of
macro fouling
Localized corrosion
in sediment
Seaweed
Mussels
Tunicates,
Hydroids,
Sponges
Clusters
of mussels
Types of fouling
HWL
LWL
! ALWC !
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MIC in maritime environment
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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Diversity in corrosion related microorganisms
Not only SRB are relevant for MIC!
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Table 2.1 Brock Biology of Microorganisms 11/e, © Pearson Prentice Hall, Inc.
Diversity of microorganisms
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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Situation: mooring piles coated only above low water
level (LW); uncoated below LW and in soil
Perforations after 5 years just below LW-level;
Some piles broken within 5 years
Corroded locations characterized by:
- Very severe local attack from outside
- Pits were bowl shaped, covered by red-orange
colored corrosion products
- Underneath blank shiny steel
- No fouling on corroded spots
Mooring pile in a small salt water harbour
MIC in maritime environment
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HT-LT zone
Aerobes SRB
SOB
MIC in maritime environment
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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Anaerobic conditions under a biofilm
Within the biofilm corrosion by Sulfate Reducing Bacteria (SRB)
Pitting corrosion with iron sulfide as corrosion product.
Biofilm is frequently disturbed by mooring ships and tidal movements
Oxygen access to metal surface aerobic conditions
Sulfur compounds are oxidized by aerobic bacteria to sulfuric acid, leading
to serious local attack and providing substrate for SRB
Mooring pile case
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MIC in maritime environment
Coating samples were exposed to suspensions with different strains of bacteria:
Sulfur oxidizing and acid producing bacterium, Acidothiobacillus thiooxidans
Slime forming bacterium that creates local chemical gradients, Pseudomonas fluorescens
Sulphur reducing and very corrosive bacterium Desulfovibrio indonesiensis
Mixed bacterial biofilm collected from a coated ballast tank
Exposure experiments were conducted at 28 ̊C for a period of 60 days;
Barrier properties of coatings were determined by EIS measurements
Microbial attack of protective coating
Objective: are tank coatings sensitive to microbial degradation?
A solvent free pure epoxy ballast water tank coating was investigated in two ways:
Applied onto stainless steel panels for EIS measurements
As a free film to observe coating degradation
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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MIC in maritime environment
Barrier properties of BWT coating exposed to bacteria
S. Indonesiensis
Conclusion: Specific bacteria can have strong negative effect on protective properties of ballast tank coatings
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MIC in maritime environment
Microbial attack of protective coatings
Exposure of free film epoxy coating to solutions with the mixed bacterial biofilm
showed striking results.
a) Flask with isolated bacteria without
medium and coating material: no growth!
b) Flask with coating flakes without bacteria:
no degradation!
c) Flask with isolated bacteria without
medium but with coating flakes: growth!
d) Flask with bacteria in their medium and
with coating flakes: growth!
Conclusion: Ballast tank coatings can be sensitive to biodegradation
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MIC in maritime environment
After 1 year
Analysis showed presence and activity of MIC relevant MO’s
Tubercles of corrosion products; underneath corrosion pits
Coupons at the inside:- close to air/water interphase, corrosion rate of 0.14 mm/year - close to the sediment, corrosion rate of 0.05 - 0.1 mm/ year
Mini monopile test setup
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water-sediment interphase
air-water interphase
submerged
Mini monopile after 7 years
MIC in maritime environment
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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Simple test set-up: exposure of carbon steel coupons in flasks with natural seawater and sand /sediment samples
MIC at water/ sediment interphase
Seawater
Sediment
carbon steel: 6 months exposure
Laboratory tests for offshore wind
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Seawater
Sediment
carbon steel: 6 months exposure
Attacked surface area with maximum pith depth around 240 µm
Average pit depth: 34 µm
Laboratory tests for offshore wind
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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MIC Diagnosis
Case by case approach
Combine different knowledge fields and experimental techniques
Mere presence of microorganisms is not enough !
Are MO’s active and is there a relationship with the damage pattern?
Are necessary nutrients available?
MIC yes or no ?
... MIC diagnosis is like a puzzle ...
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MIC diagnosis and failure analysis
Case documentation
Microbial analysis (e.g. growth- &
DNA based)
Microbial related failure analysis
Detect or exclude other corrosion
mechanisms
ATP tests
Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
Detect or exclude other corrosion mechanisms
Other corrosion mechanisms are often not taken into account: Failure in the choice of a suitable mitigation strategy MO’s are found present but their activity is not established or investigated Often MIC is “blamed” when other explanations cannot be given
“Chicken or egg” question: what was first? Wrong choice/ failure of material/ no protection of material
or Presence and activity of microorganisms
MIC may take place regularly in conjunction with other corrosion mechanisms:
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Galvanic corrosion
Stray current
Under deposit corrosion
MIC diagnosis and failure analysis
1 Coatings: Correct choice of coating (part of structure, exposure conditions, lifetime, …) Proper application (surface pre-treatment and condition, equipment, ...) Difficult for mudline or area under seabed
Metallization (TSZ, TSA) seems to be promising but further investigations required, for instance in offshore wind
2. Cathodic protection: Depending on potential applied and maybe also on MO’s present Install and operate CP right from the beginning! Late installment and
interruptions may give problems
CP will probably work but optimal settings and conditions are still under investigation Cases are described in which biofilm formation was stimulated when using CP
3. Other mitigation strategies Biocides, corrosion inhibitors UV light, ultrasound
Chemicals often not possible in open systems; physical methods still under investigation
Prevention and mitigation of MIC
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Antwerp Corrosion & Fouling Meeting 2019 01-4-2019
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Take home messages
MIC needs to be analyzed on a case by case basis
Other corrosion mechanisms need to be established or ruled out
Investigate not only the presence but also the activity of MIC relevant MO’s
Numbers of MO’s from test kit results are useless unless a clear relationship with the (damaged) metal is established
There is not one “powerful tool” against MIC, it is a combination of multiple factors
Activity of corrosion related MO’s should be monitored/ controlled for proper protection of maritime structures against MIC
Think about a prevention strategy before the structure is installed
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Questions ?