Biofouling and microbial corrosion problem in the thermo-fluid heat exchanger and cooling water system of a nuclear test reactor

This article discusses aspects of biofouling and corrosion in the thermo-fluid heat exchanger (TFHX) and in the cooling water system of a nuclear test reactor. During inspection, it was observed that >90% of the TFHX tube bundle was clogged with thick fouling deposits. Both X-ray diffraction and Mössbauer analyses of the fouling deposit demonstrated iron corrosion products. The exterior of the tubercle showed the presence of a calcium and magnesium carbonate mixture along with iron oxides. Raman spectroscopy analysis confirmed the presence of calcium carbonate scale in the calcite phase. The interior of the tubercle contained significant iron sulphide, magnetite and iron-oxy-hydroxide. A microbiological assay showed a considerable population of iron oxidizing bacteria and sulphate reducing bacteria (10⁵ to 10⁶ cfu g^?1 of deposit). As the temperature of the TFHX is in the range of 45–50°C, the microbiota isolated/assayed from the fouling deposit are designated as thermo-tolerant bacteria. The mean corrosion rate of the CS coupons exposed online was ～2.0 mpy and the microbial counts of various corrosion causing bacteria were in the range 10³ to 10⁵ cfu ml^?1 in the cooling water and 10⁶ to 10⁸ cfu ml^?1 in the biofilm.     

Corrosion behaviour and biofouling characteristics of structural steel in the coastal waters of the Gulf of Mannar (Bay of Bengal), India

The corrosion behaviour and biofouling characteristics of structural steel coupons at three different locations in the Gulf of Mannar were studied over a period of 2 years. Oyster fouling was predominant at Tuticorin open sea, while barnacle fouling was more pronounced at Mandapam and Tuticorin harbour. Among the three locations, Tuticorin open sea showed a markedly higher biomass, particularly after 12 and 18 months. The extent of crevice corrosion caused by hard foulers was more pronounced at Tuticorin harbour when compared to that at the other two locations. The corrosion rate of the structural steel coupons for 24 months was in the order, Mandapam > Tuticorin harbor > Tuticorin open sea. The loss in tensile strength at 12 and 24 months was in the order, Tuticorin open sea > Tuticorin harbor > Mandapam. The corrosion behaviour of the structural steel coupons was strongly influenced by the variations in the biofouling assemblage at the three different coastal locations.     

Anaerobic microbial activities including hydrogen mediated acetogenesis within natural gas transmission lines

Microbially influenced corrosion (MIC) is being increasingly recognised as a serious problem. To investigate the role of MIC, radiotracer activity and lipid biomass measurements were performed on samples from offshore and on‐shore natural gas transmission systems. These measurements evaluated the biomass and metabolism of microbial communities residing inside transmission pipelines. Aqueous and nonaqueous hydrocarbon samples from liquid separators, sludge catchers and nodules attached to pipe walls were aseptically recovered and inoculated into anaerobic tubes for radiotracer time course experiments or preserved with chloroform‐methanol for total lipid analyses. MPN enrichments and phospholipid biomass determinations estimated microbial populations of 10⁴—10⁷ cells per gram in several samples. General microbial metabolism was demonstrated by [l‐¹⁴C]acetate incorporation into lipids and by [¹⁴C]CO₂ production from [U‐¹⁴C]glucose. [¹⁴C]Acetate was slowly mineralised to ¹⁴CO₂ without significant methane production. [¹⁴C]Acetate was produced by fermentation of [¹⁴C]glucose, [¹⁴C]palmitate and by hydrogen mediated acetogenesis in the presence of [^I4C]CO₂. In one location acetogenesis from hydrogen and carbon dioxide accounted for 0–7 mmol.l^‐1 of acetate production per week. These results demonstrated that microorganisms could utilise natural gas impurities to produce organic acids. This activity could adversely affect the structural integrity (MIC) of high pressure natural gas pipelines.     

Biodeterioration of dental materials: Influence of bacterial adherence

The aim of this work was to carry out a comparative study of microbial adhesion on dental alloys and glass ionomers that release fluoride. The action of NaF on the early stages of biofilm development and on the corrosion of the metallic dental materials was analysed. Open circuit potential measurements and potentiostatic electrochemical techniques with different perturbation programs as well as SEM observations, and optical and epifluorescence microscopy were employed. A notable effect of topography and the nature of the substratum on bacterial distribution was observed. In addition, changes in the density and thickness of microbial colonies were noticed when fluoride was present. The results show that the antimicrobial effect of fluoride was significant against planktonic but not against sessile microorganisms. Fluoride released by glass ionomers did not impede bacterial adhesion to the surface. With respect to corrosion, fluoride did not alter significantly the passivity of the dental metallic biomaterials assayed, except for Cu‐Al alloy. Titanium dissolution could occur at high fluoride concentrations (8gl^‐1) during oxide layer formation. Consequently, bacterial adherence was influenced by the nature and topography of the substratum and by the presence of fluoride which could also affect the electrochemical behaviour of some metallic substrata.     

An assessment of alternative diesel fuels: microbiological contamination and corrosion under storage conditions

Experiments were designed to evaluate the nature and extent of microbial contamination and the potential for microbiologically influenced corrosion of alloys exposed in a conventional high sulfur diesel (L100) and alternative fuels, including 100% biodiesel (B100), ultra-low sulfur diesel (ULSD) and blends of ULSD and B100 (B5 and B20). In experiments with additions of distilled water, all fuels supported biofilm formation. Changes in the water pH did not correlate with observations related to corrosion. In all exposures, aluminum 5052 was susceptible to pitting while stainless steel 304L exhibited passive behavior. Carbon steel exhibited uniform corrosion in ULSD and L100, and passive behavior in B5, B20, and B100.     

Iron cycling at corroding carbon steel surfaces

Surfaces of carbon steel (CS) exposed to mixed cultures of iron-oxidizing bacteria (FeOB) and dissimilatory iron-reducing bacteria (FeRB) in seawater media under aerobic conditions were rougher than surfaces of CS exposed to pure cultures of either type of microorganism. The roughened surface, demonstrated by profilometry, is an indication of loss of metal from the surface. In the presence of CS, aerobically grown FeOB produced tight, twisted helical stalks encrusted with iron oxides. When CS was exposed anaerobically in the presence of FeRB, some surface oxides were removed. However, when the same FeOB and FeRB were grown together in an aerobic medium, FeOB stalks were less encrusted with iron oxides and appeared less tightly coiled. These observations suggest that iron oxides on the stalks were reduced and solubilized by the FeRB. Roughened surfaces of CS and denuded stalks were replicated with culture combinations of different species of FeOB and FeRB under three experimental conditions. Measurements of electrochemical polarization resistance established different rates of corrosion of CS in aerobic and anaerobic media, but could not differentiate rate differences between sterile controls and inoculated exposures for a given bulk concentration of dissolved oxygen. Similarly, total iron in the electrolyte could not be used to differentiate treatments. The experiments demonstrate the potential for iron cycling (oxidation and reduction) on corroding CS in aerobic seawater media.     

Anticorrosion mechanism of Cr-doped nickel-base alloy in Br/O environment: a DFT study

ABSTRACT

Density functional theory was used to investigate the anticorrosion mechanism of Cr-doped nickel-base alloy in Br/O environment. The adsorption properties including adsorption energy, bond length and electron structure of Br/O on Ni and Cr-doped Ni surfaces have been investigated. We find that the O atom has bigger adsorption activity than the Br atom. The oxide film can be preferentially formed on the Cr-doped nickel-base alloy surface under the coexistence of Br and O atoms. By exploring the interactions between Br and NiO (111) or Cr₂O₃ (100) surfaces, we demonstrate that oxide films could prevent Br from erosion. Results indicate that Cr₂O₃ has stronger corrosion resistance than NiO. The corrosion resistance mechanism of Cr-doped nickel-base alloy is summarised into two processes, i.e. competitive adsorption and adsorption inhibition.     

Middle Triassic horseshoe crab reproduction areas on intertidal flats of Europe with evidence of predation by archosaurs

A systematically excavated track site in a 243.5 Myr old Middle Triassic (Karlstadt Formation, Pelsonian, middle Anisian) intertidal carbonate mud‐flat palaeoenvironment at Bernburg (Saxony‐Anhalt, central Germany) has revealed extensive horseshoe crab trackways attributable to the Kouphichnium Nopsca, 1923 ichnogenus. The exposed track bed of a Germanic Basin‐wide spanned intertidal megatrack site is a mud‐cracked biolaminate surface on which detailed tracks have been preserved because of rapid drying and cementation as a result of high temperatures, followed by rapid covering with a protective layer of arenitic storm or tsunami sediments. The different trackway types and their orientations have allowed a tidal sequence to be reconstructed, with the initial appearance of swimming horseshoe crabs followed by half‐swimming/half‐hopping limulids under the shallowest water conditions. The Bernburg trackways, which have mapped lengths of up to 40 m, were all produced by adult animals and exhibit a variety of shapes and patterns that reflect a range of subaquatic locomotion behaviour more typical of mating than of feeding activities. The closest match to the proportions and dimensions of the horseshoe crab tracks at Bernburg is provided by the largest known Middle Triassic limulid Tachypleus gadeai, which is known from the north‐western Tethys in Spain. The horseshoe crab body fossils recognized in the German Mesozoic intertidal zones, instead, are from juveniles. The uniformly adult size indicated by the trackways therefore suggests that they may record the oldest intertidal reproductive zones of horseshoe crabs known from anywhere in the world, with the track‐makers having possibly migrated thousands of kilometres from shallow marine areas of the north‐western Tethys to reproduce in the intertidal palaeoenvironments of the Germanic Basin. Chirotherium trackways of large thecodont archosaurs also appeared on these flats where they appear to have fed on the limulids. With the tidal ebb, smaller reptiles such as Macrocnemus (Rhynchosauroides trackways) appeared on the dry intertidal flats, probably feeding on marine organisms and possibly also on horseshoe crab eggs. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 76–105.