Test have performed at about 25 deg C in both natural and chlorinated sea waters on couples of nickel-aluminium bronze (NAB) and Zeron 100 (Z100) superduplex stainless steel. Two NAB/Z100 area ratios (1:1 and 1:10) were used in exposures of 60 days. The results in natural sea water showed severe localised corrosion of NAB both in the crevices and on open surfaces at both area ratio. The attack is explained in terms of the different cathodic reactions occurring in natural and chlorinated sea waters, and the metallurgical structure of NAB. Service experiences with couples of NAB and superduplex stainless steel are described and recommendations are given for the avoidance of problems. Nickel-aluminium bronze should not be coupled to Z100 in natural sea water unless the area of NAB greatly exceeds that of the stainless steel (e.g. a stainless steel pump shaft or a valve stem). NAB can be coupled to Z100 piping in chlorinated sea water (0.5-1.0 mg/L chlorine) provided the crevice areas are protected and the temperature is <= 25 deg C. The flanges are normally cast-in and form a substantial crevice with the gasket. These can be protected with a high integrity coating such as coal tar epoxy, fusion bond epoxy, etc. The stem and seat need to be compatible with the pipework so that no corrosion occurs in this area and the valve will always close properly. Suitable alloys for this area are Z100, C-276, alloy 625, and wear resisting alloys such as Stellite 6 and Ultimet. Although there will be some increase in the corrosion rate of the valve body, this should not be serious as the valve body will be of substantial thickness (> 15 mm). Regular refreshment of the water in close valves would be beneficial to prevent sulphide attack.


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    Titel :

    Coupling of superduplex stainless steel and cast nickel-aluminium bronze in sea water


    Weitere Titelangaben:

    Paarung von nichtrostendem Super-Duplexstahl und Nickel-Aluminium-Gußbronze in Seewasser


    Beteiligte:
    Francis, R. (Autor:in)

    Erschienen in:

    British Corrosion Journal ; 34 , 2 ; 139-144


    Erscheinungsdatum :

    1999


    Format / Umfang :

    6 Seiten, 11 Bilder, 2 Tabellen, 8 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch