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In this article we describe a field study of biofouling and microbiologically influenced corrosion (MIC) of admiralty brass heat exchanger tubes in contact with running fresh water on the river Tagus close to Almaraz nuclear power plant in Spain. Dezincification originated by biofouling and MIC was studied using impedance, polarization resistance, gravimetric, scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements. Close correlation was observed between the biofilms formed and the corrosion process (dezincification) using the different experimental techniques. Impedance data showed a capacitive behavior including two time constants. Kramers-Kronig (KK) transforms were used to validate impedance data. The admiralty tubes' impedance data satisfied the KK relations.

The effect of aggressive anions chloride and sulfide and their mixtures on the localized corrosion resistance of type 410 (UNSI' ) S41000) stainless steel (SS) has been studied. A synergistic effect of these anions on pitting attack was found. The quenched condition offers the highest resistance followed by the asreceived condition. Tempered states show worse corrosion resistance than the other states. A comparison between the effect of biogenie and inorganic sulfides and the study of bacterial adhesion on type 410 SS surfaces were made. The adhesion of Desulfovibrio vulgaris on the metal probes facilitated localized attack in chloride media. KEY WORDS: bacterial adhesion, biofilms, biogenic sulfide, MIC, microstructure, pitting behavior, sulfate-reducing bacteria, type 410 SS 16. H. ABSTRACTThe batch-type hot-dip Zn and 5 %AI-Zn coatings were investigated in the present work for correlations between their corrosion resistance, electrochemical behaviors, and microstructures. The microstructures of the coatings were altered with air cooling and water quenching for studying the corrosion resistance mechanism. Polarization curves can distinguish the layering character of the Zn coating. The 5%AI-Zn coatings possess prominent electrochemical passivation behavior. Intermetallic layers formed mainly between Fe and Al, adhering to substrate, were identified with energy-dispersive x-ray analysis and were believed to be responsible for the passivation phenomena observed in polarization curves. Faster cooling speed tends to lower the corrosion potent/al, Ecorr, on the basis of polarization measurement of the zinc but not the 5%A1-Zn coating and significantly affects the corrosion resistance of both coatings. The open-circuit potential as well as the galvanic coupling currents were also investigated for the coatings.