Both laboratory and field immersion tests were conducted on Monel 400 alloy to assess its susceptibility towards microbial attack in Arabian Gulf seawater. Specimens were exposed to chlorinated and non-chlorlnated seawater for periods up to four months. Other tests included exposure of Monel to a prepared active sulphate-reducing bacterial culture (SRB). The results indicated that SRB attack is initiated beneath a black sulphide-rich deposit, overlaid by a green chlorlde-rlch deposit and occasionally a beige-coloured scale was found on top. The black layer was found to be comprised mainly of one or more of iron nickel sulfides (Fe,Nl)xSy, whereas the green layer was found to be essentially composed of CuCl2.3Cu(OH)2 and a low concentration of NiCl2. The beige layer was a calcareous deposit. These deposits were in the form of nodules scattered on the surface and, when removed, circular attacked areas or cavities were revealed. SEM examinations of these areas indicated severe intergranular corrosion below which a copper-rich alloy was detected.

Subject
Scanning electron microscopy, Materials, Metal surfaces, Iron sulfides, Iron, Corrosion detection, Nodules, Seawater, Corrosion products, Corrosion attacks, Microbial corrosion, Monel alloys, Nickel
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1990
Association for Materials Protection and Performance (AMPP)
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