A survey of ports in five west European countries has shown that 36 (12-13 %) are affected by low water corrosion (LWC) of steel piling structures. This takes the form of severe corrosion, at or just below the mean low water mark, reducing significantly the effective life of the structure. Electrochemical corrosion m onitoring has been carried out at four of the affected ports; potential measurements have been made on existing piling structures and laboratory tidal simulation tests have been undertaken. These have shown that significant macro-anodic and macro-cathodic areas a formed initially at the low water level and in the tidal zone, respectively. These, however, do not persist and after about 200 days no significant potential difference exists or corrosion current occurs between these zones. Therefore, the macro-electrochemical effects do not provide a viable explanation of the LWC phenomenon. Detailed examination of corrosion products and other deposits on sheet piling walls has shown that the characteristic black liquid sludge film found next to the steel surface only at the low water level, contains high levels of iron sulphide, probably in an acidic solution, in the absence of free oxygen. Mössbauer spectroscopy has shown that this black film contains large quantities of Green Rust II, an unstable iron complex which has been linked to corrosion by sulphate reducing bacteria (SRB). In many cases, SRB have been found in high numbers around the LWC holes. No correlation has been found between the total numbers of SRB found and the location of the LWC holes. However, the composition of the SRB bacterial population has been shown to be different in these areas and its activity has been shown to be greater than in those regions not exhibiting the LWC phenomenon. Certain species of aerobic bacteria have been shown to form microbial consortia with SRB around the LWC holes and to be associated with the corrosion process. Linear polarisation resistance tests and corrosion weight loss tests have shown that bacteria from around LWC holes can cause a very significant increase in the corrosion of steel. These results and other assembled data provide a considerable mass of circumstantial evidence that LWC is microbially induced.


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    Title :

    Low-water corrosion on steel piles in marine waters


    Additional title:

    Niedrigwasserkorrosion an Spundpfählen in europäischen Meeereshäfen


    Contributors:
    Johnson, K. (author) / Moulin, J. (author) / Karius, R. (author) / Resiak, B. (author) / Confente, M. (author) / Chao, W. (author)


    Publication date :

    1997


    Size :

    119 Seiten, 64 Bilder, 18 Tabellen, 65 Quellen




    Type of media :

    Report


    Type of material :

    Print


    Language :

    English






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