Papers by Keyword: Microbial Corrosion

Abstract: This study presents the results of both non-destructive (radiography and computed tomography) and destructive (light optical and scanning electron microscopy) evaluations of operational degradation in welded joints of ESW (electroslag welding) pipelines. Microbiologically influenced corrosion (MIC), potentially induced by manganese-oxidizing microorganisms (MOMOs), was investigated as a plausible degradation mechanism. Extensive subsurface corrosion cavities were identified beneath the internal surface of the pipelines. The presence of MnO₂ globules near these cavities supports the hypothesis of MOMO-induced corrosion.

Abstract: Although much less investigated than that induced by chlorides, the corrosion of steel reinforcing bars due to bacteria metabolic products is recognised as a serious issue, primarily for concrete pipes in sewer network. In order to overcome the complications due to the preparation of concrete samples the investigation was performed using simulating solutions. The passivation of the metallic specimens was obtained by immersion in Ca (OH)_{2 sat} and monitored through several different electrochemical techniques. The depassivation was induced by either sulphuric acid or sulphides in order to simulate different bacterial metabolites. Anodic polarization curves and optical microscopy examination revealed a significant corrosion in the former case, while a competitive interaction among the sulphide and the alkalinity was hypothesized in sulphide-containing solutions.

Abstract: Crevice corrosion (CC) was investigated for a number of selected corrosion resistant alloys in natural seawater containing microorganisms for up to 18 months under stagnant conditions. Experimental controls consisted of tests in natural seawater filtered in accordance with hydrostatic testing procedures. The corrosion potential of alloys was monitored throughout exposure and corrosion was evaluated by weight loss and 3D optical microscopy. CC was initiated on several alloys and corrosion rates in time indicated a positive effect of seawater filtration on the long-term performance of the alloys. Microbial adhesion, as indicated by fluorescence microscopy, occurred mainly outside the crevice and differed according to the nature of the substratum surface.

Abstract: Polarization curves, corrosion potential, scanning electron microscopy (SEM) were adopted to investigate the corrosion behaviors of QSn4-3 under two kinds of marine advantage bacteria (anaerobic SRB and facultative anaerobic Vibrio natriegens) environment. The results show that the microbial film has some effects on inhibiting corrosion of QSn4-3 at the early stage of corrosion; the existence of marine microorganisms accelerates the corrosion process of QSn4-3; the combined action of SRB and V.natriegens accelerates the corrosion obviously and QSn4-3 coupon is more prone to pitting corrosion.

Abstract: Microbial biofilms produce electrochemical interactions with metal surfaces by following a wide variety of different electron exchange pathways. Reviewing the mechanisms identified in the biocorrosion of steels leads us to distinguish direct and indirect mechanisms for biofilm-catalysed cathodic reactions. Indirect mechanisms are due to the production of metal oxides or hydrogen peroxide (aerobic corrosion) or metal sulphides (anaerobic corrosion), which further react with the metal surface. Direct mechanisms involve adsorbed biocompounds, generally enzymes or their active sites, which catalyse the cathodic reduction of oxygen for aerobic biocorrosion or the proton/water reduction in anaerobic processes. Recent studies dealing with the role of hydrogenases in anaerobic corrosion have shed light on the important role of phosphate species via so-called cathodic deprotonation. Advances in the development of microbial fuel cells have also resulted in new concepts, mainly for oxidation processes. Some microbial cells have been shown to be able to produce their own electron mediators. Others can transfer electrons directly to electrodes through membrane-bound electron shuttles or achieve long-range transfer through conductive pili.