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Protection against microbiological corrosion and developments in corrosion detection. Corina Prent Contents • • • • Corrosion Microbial interaction with iron Prevention off microbial corrosion New technology for detecting corrosion Corrosion The corrosion process: electrochemical interaction between a metallic material and its environment. Corrosion occurs because of the natural tendency for most metals to return to oxidized species in nature in ores. (Jones, 1995; Groysmann, 2010. hematite α-FeOOH The corrosion rate influenced by: • • • • • • pH Temperature Microorganisms Type of metal Presence of surface films (coatings-biofilm) Mechanical properties (stresses). B.W.A. Sherar, Corrosion Sci. 53 (2011) 955-960 Microorganism and Iron in a maritime environment • Metabolism • Create a local environment 4 Microorganism : Metabolism Black smokers, deepsea • Hydrothermal vents: • Water with 60 °C T< 464 °C • Depth 5 km • No light • Complete ecosystem, based on iron oxidization? Microorganism : Metabolism Titanic wreck: • Depth: 3000 meter • Temperature :1–2 °C • No licht 2010 Halomonas titanicae Situation: Local Environment: corrosion • salt water harbour • wall thickness 8.8 mm, • uncoated beneath Low Water Level and in soil, • coated above Low Water Level Gallionella Source: TNO, Maritime Materials Performance Centre 7 Local Environment: corrosio Duluth-Superior Harbour Accelerated Freshwater Corrosion Protection & Remediation of Structures in Cold Regions Scribe to bare metal to simulate impact Ice Abrasion Samples after Installation MATERIALS PERFORMANCE October 2008 Microbial corrosion • Localized aggressive form of corrosion • Unpredictable uncontrolled • Average cost of corrosion is 5% BNP 50% caused by MIC • Failures that are of environmental concern or even hazardous ballast water tanks A. Heyer at all, Ocean Engineering 70 (2013) 188–200 9 Microbial corrosion Can occur everywere even in: – Arctic – Deep sea Microbial corrosion can also apply to: – – – – Plastics Concrete Coatings Adhesives Microbial corrosion • Requirements: • Presence of moisture • Micro-organisms require water to propagate • Substrate (host location) • Presence of nutrient • Nutrients depletion micro-organisms remain dormant • Nutrients are restored microbial growth resumes • Under aerobic and anaerobic circumstances 11 Bacteria involved: • Slime forming (e.g. Pseudomonas spp.) • Sulfate reducing bacteria (SRB) Pseudomonas (e.g. Desulfovibrio spp.) • Acid producing bacteria (APB) (e.g. Acidithiobacillus thiooxidans) • Iron oxidising bacteria (e.g.Acidithiobacillus ferrooxidans) Patchy biofilm stained with SYTO13 SEM image of SRB 12 General mechanism of MIC • Electrochemical reaction • Uneven distribution of biofilm formation of different aeration cells with anodic and cathodic sites • Production of corrosive metabolites or may precipitate directly the metal into the solution patchy biofilm results in localized corrosion (pitting corrosion) 13 Prevention methods for MIC 1. Change environment 2. Add biocides Only possible in confined spaces 3. Pulsing cathodic-anodic protection 4. Generation of protective layer Biofilm growth 5. Growth inhibition corrosion causing bacteria Anti microbial 6. Coating General Causes of coating failures (new built) • Surface preparation • Coating application • Coating properties 16-09-2010 Causes of coating failures (during service) • Degradation due to environmental effects • Mechanical damages • Poor maintenance and cleaning • Microbial attack Example Commercial (ballast) tank coating, after 10 weeks of exposure. Staining of micro-organism around the corrosion pit FeS Synthetic seawater With SRB 16-09-2010 Around the pit In the pit Coating degradation by microorganism Biofilms, bacteria can influence the degradation and consequently the protective properties of the coating. – By feeding themselves with compounds from the coating. – By locally changing the circumstances (parameters)on the coating. Organisms (can) have different roles in the deterioration of the coating and in the corrosion attack. MID is difficult to predict: living organisms + imperfections in the coatings. Humidur by ACOTEC is resistent against micobial degradation University of Ghent 16-09-2010 Moscow Eurocorr2010 18 Detection • Sensors for corrosion: – To late – To local • Sensor’s to determine if a biofilm is present – No discrimination between good en bad film • Sensors to determine coating degradation – EIS • Cumbersome • Difficult to interpret • Local measurement Schematic set-up and analysis of EIS measurements Perfecte barrier coating Ag/AgCl Ref. electrode Pt counter electrode EIS set up for coating degradation measurements Elektrochemical processes occurring 16-09-2010 Moscow Eurocorr2010 20 New Principle for easy method ZRA E ‘Fingerprinting’ Working electrodes Reference electrode Electrolyte Individual localized processes A.M. Homborg, Electrochemical Acta, 70 (2012) 199-205 Advantages ‘Fingerprinting’ individual corrosion phenomena at any given moment in time Identify and distinguish between different corrosion mechanisms passive technique; non-disturbing Valuable in corrosion monitoring by future fully automated detection of specific corrosion phenomena Simplicity of the sensor: Robust, reliable and cheap Aim Corrosion type/cause Corrosion attack None Severe User level Condition based maintenance Decision support Maintainer level Acknowledgements • M2I – Anne Heyer – Axel Homborg • TNO – – – – – Fraddy D’Souza/Felipe Leon Morales Gabriele Ferrari Job Klijnstra Gijsbert Strijk Anouk de Bruin • 3mE TU Delft – Arjan Mol – Hans de Wit 24