Leena Carpén

Biofilm development during ennoblement of stainless steel in Baltic Sea water: A microscopic study

This paper describes the development of biofilm on stainless steel during the increase of open circuit potential (ennoblement, Ecorr) that follows the exposure of AISI 316 stainless steel to natural seawater. The ennoblement occurred in the laboratory model ecosystem (mesocosm) reproducibly and similarly to that observed under field conditions in the Baltic Sea, provided that natural seawater was used as the feed, and the hydraulic flow was sufficiently high (10–30 mm s−1). Features distinguishing the ennobling biofilm from the non-ennobling, were studied using scanning (SEM) and transmission electron microscopy (TEM) as well as confocal laser scanning microscopy (CLSM). The increase of open circuit potential started in the laboratory (23°C±1) after 8 days and was complete (ΔE of 300–500 mV) after 21 days. In the field (10–14°C), ennoblement progressed from 21 days to 42 days (δE of 400–500 mV). When more than ten initially adhered cells per mm2 had grown into mushroom-like structures of > 50 μm in diameter and > 10 μm in height, covering 1–5% of the steel surface, the ennoblement started. The potential continued to increase while the biofilm mushrooms grew in height to 100 μm, and reached a plateau at 300–400 mV vs. SCE (standard calomel electrode) when the coverage of the steel surface reached 10–20%. Compared to the non-ennobling biofilms, those on the ennobled stainless steels attached more firmly to steel, were impermeable to lipophilic (acridine orange) and hydrophilic (lectin conjugates) dyes and grew as individual biofilm mushrooms of an average size of 0.5…2×106 μm3 containing 0.3–1×106 of tiny (< 1 μm) bacterial cells dispersed in interstitial matter. Biofilms on nonennobled stainless steels in the same seawater were easily removable, fluffy and permeable. The option of explaining the ennoblement (increase of cathodic reaction) of the stainless steel by microbial oxidation of organic residues inside the impermeable biofilm mushroom at the expense of Fe3+ reduction is discussed.

Microbially induced corrosion of carbon steel in deep groundwater environment

The metallic low and intermediate level radioactive waste generally consists of carbon steel and stainless steels. The corrosion rate of carbon steel in deep groundwater is typically low, unless the water is very acidic or microbial activity in the environment is high. Therefore, the assessment of microbially induced corrosion of carbon steel in deep bedrock environment has become important for evaluating the safety of disposal of radioactive waste. Here we studied the corrosion inducing ability of indigenous microbial community from a deep bedrock aquifer. Carbon steel coupons were exposed to anoxic groundwater from repository site 100 m depth (Olkiluoto, Finland) for periods of 3 and 8 months. The experiments were conducted at both in situ temperature and room temperature to investigate the response of microbial population to elevated temperature. Our results demonstrate that microorganisms from the deep bedrock aquifer benefit from carbon steel introduced to the nutrient poor anoxic deep groundwater environment. In the groundwater incubated with carbon steel the planktonic microbial community was more diverse and 100-fold more abundant compared to the environment without carbon steel. The betaproteobacteria were the most dominant bacterial class in all samples where carbon steel was present, whereas in groundwater incubated without carbon steel the microbial community had clearly less diversity. Microorganisms induced pitting corrosion and were found to cluster inside the corrosion pits. Temperature had an effect on the species composition of microbial community and also affected the corrosion deposits layer formed on the surface of carbon steel.

Influence of Chlorination and Choice of Materials on Fouling in Cooling Water System under Brackish Seawater Conditions

Cooling systems remove heat from components and industrial equipment. Water cooling, employing natural waters, is typically used for cooling large industrial facilities, such as power plants, factories or refineries. Due to moderate temperatures, cooling water cycles are susceptible to biofouling, inorganic fouling and scaling, which may reduce heat transfer and enhance corrosion. Hypochlorite treatment or antifouling coatings are used to prevent biological fouling in these systems. In this research, we examine biofouling and materials’ degradation in a brackish seawater environment using a range of test materials, both uncoated and coated. The fouling and corrosion resistance of titanium alloy (Ti-6Al-4V), super austenitic stainless steel (254SMO) and epoxy-coated carbon steel (Intershield Inerta160) were studied in the absence and presence of hypochlorite. Our results demonstrate that biological fouling is intensive in cooling systems using brackish seawater in sub-arctic areas. The microfouling comprised a vast diversity of bacteria, archaea, fungi, algae and protozoa. Chlorination was effective against biological fouling: up to a 10–1000-fold decrease in bacterial and archaeal numbers was detected. Chlorination also changed the diversity of the biofilm-forming community. Nevertheless, our results also suggest that chlorination enhances cracking of the epoxy coating.

Nitrate and ammonia as nitrogen sources for deep subsurface microorganisms

We investigated the N-utilizing bacterial community in anoxic brackish groundwater of the low and intermediate level nuclear waste repository cave in Olkiluoto, Finland, at 100 m depth using 15N-based stable isotope probing (SIP) and enrichment with 14∕15N-ammonium or 14∕15N-nitrate complemented with methane. Twenty-eight days of incubation at 12°C increased the concentration of bacterial 16S rRNA and nitrate reductase (narG) gene copies in the substrate amended microcosms simultaneously with a radical drop in the overall bacterial diversity and OTU richness. Hydrogenophaga/Malikia were enriched in all substrate amended microcosms and Methylobacter in the ammonium and ammonium+methane supplemented microcosms. Sulfuricurvum was especially abundant in the nitrate+methane treatment and the unamended incubation control. Membrane-bound nitrate reductase genes (narG) from Polarimonas sp. were detected in the original groundwater, while Burkholderia, Methylibium, and Pseudomonas narG genes were enriched due to substrate supplements. Identified amoA genes belonged to Nitrosomonas sp. 15N-SIP revealed that Burkholderiales and Rhizobiales clades belonging to the minority groups in the original groundwater used 15N from ammonium and nitrate as N source indicating an important ecological function of these bacteria, despite their low number, in the groundwater N cycle in Olkiluoto bedrock system.

Microbial fouling and corrosion of carbon steel in deep anoxic alkaline groundwater

Abstract Understanding the corrosion of carbon steel materials of low and intermediate level radioactive waste under repository conditions is crucial to ensure the safe storage of radioactive contaminated materials. The waste will be in contact with the concrete of repository silos and storage containers, and eventually with groundwater. In this study, the corrosion of carbon steel under repository conditions as well as the microbial community forming biofilm on the carbon steel samples, consisting of bacteria, archaea, and fungi, was studied over a period of three years in a groundwater environment with and without inserted concrete. The number of biofilm forming bacteria and archaea was 1,000-fold lower, with corrosion rates 620-times lower in the presence of concrete compared to the natural groundwater environment. However, localized corrosion was detected in the concrete–groundwater environment indicating the presence of local microenvironments where the conditions for pitting corrosion were favorable.

Ennoblement, corrosion, and biofouling in brackish seawater: Comparison between six stainless steel grades

In this work, six common stainless steel grades were compared with respect to ennoblement characteristics, corrosion performance and tendency to biofouling in brackish sea water in a pilot-scale cooling water circuit. Two tests were performed, each employing three test materials, until differences between the materials were detected. Open circuit potential (OCP) was measured continuously in situ. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements were conducted before and after the tests. Exposed specimens were further subjected to examinations by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), and the biofouling was studied using epifluorescence microscopy, quantitative polymerase chain reaction (qPCR) and high-throughput sequencing (HTP sequencing). The results revealed dissimilarities between the stainless steel grades in corrosion behaviour and biofouling tendency. The test material that differed from the most of the other studied alloys was grade EN 1.4162. It experienced fastest and most efficient ennoblement of OCP, its passive area shrank to the greatest extent and the cathodic reaction was accelerated to a significant degree by the development of biofilm. Furthermore, microbiological analyses revealed that bacterial community on EN 1.4162 was dominated by Actinobacteria, whereas on the other five test materials Proteobacteria was the main bacterial phylum.

Biogenic thiosulfate and oxalate in paper machine deposits connected to corrosion of stainless steels

Abstract Pick-up felts and deposits in wet end splash areas and in storage tanks of paper machines contained large amounts of thiosulfate (80– 16 000 mg kg −1 , wet weight) and oxalate (20– 2300 mg kg −1 , wet weight). These anions were absent ( mg l −1 ) in process water and found in raw materials only in low concentrations (5– 10 mg kg −1 , wet weight). Similar and larger amounts of thiosulfate, sulfite and oxalate were generated de novo from sulfate and sheets of chemical pulp in a splash area simulator fed with artificial paper machine white water in the laboratory. Stainless steel UNS S30400 coupons placed in the simulator developed significant corrosion pits within 4 weeks. Pitting was most extensive under or vicinal to patches where large amount of thiosulfate and oxalate accumulated in the pulp sheet. Pitting of UNS S31600 occurred only vicinal to the pulp sheet. The pitted steel surfaces accumulated large amounts of silicon containing material. The biogenic conversion of sulfate into compounds of lower oxidation states occurred more extensively on stainless steel UNS S30400 than on UNS S31600.

Influence of Carbon Sources and Concrete on Microbiologically Influenced Corrosion of Carbon Steel in Subterranean Groundwater Environment

Microbiologically influenced corrosion of carbon steel was assessed in a laboratory environment simulating the deep geological repository of radioactive waste. A dense and diverse biofilm was forme...

Microbially Induced Corrosion in Firefighting Systems—Experience and Remedies

Firefighting water systems are important safety systems in all industries, including nuclear power plants (NPPs). However, they are susceptible to microbially induced corrosion, which is a degradation mode needing special attention. Leakages were observed in a fire fighting system made from stainless steel at a nuclear power plant shortly after maintenance and modernization work, which included replacement of part of the old carbon steel pipelines with stainless steel pipelines, as well as exchange of some Type 304 stainless steel pipes with Type 316 pipes due to relining parts of the system. The failure analysis revealed sub-surface corrosion cavities with pinholes at the inner surface and finally penetrating the whole pipe wall thickness. It was concluded that the reason for the leaks was due to microbially induced corrosion, (MIC). The paper will present the results from failure analyses, explain the remedial actions taken at the power plant, and discuss the implication of these findings on new similar systems, including the importance of avoiding iron deposits and optimization of water quality.