Copper Alloys and MIC

Because copper is toxic to many life forms it is often assumed that copper and its alloys do not suffer from microbially influenced corrosion (MIC).  This is not true and there are a number of ways that bacteria can affect the corrosion of copper alloys, and not all of them are detrimental.

In seawater, aluminium brass forms a protective film of hydrotalcite (Mg6Al2[OH16]CO3.4H2O), which is composed of a minor constituent of the alloy and of seawater.  This film does not form in synthetic seawater, and it is produced because natural seawater contains bacteria that chelate the copper and zinc dissolving from the alloy, and preventing them from becoming incorporated into the protective film.  This film adjusts its composition to buffer the pH at the metal surface and reduce metal dissolution.

Copper alloy corrosion can be greatly accelerated when sulphides are present, particularly in aerated waters. Sulphides are frequently generated by sulphate reducuing bacteria.  These bacteria do not usually produce sulphide on copper alloy surfaces, but become active under deaerated conditions, for example, stagnant enclosed water.  Hence the sulphide is often produced upstream of the copper alloys and the sulphide contacts them when flowing conditions resume.

Posted on: 21st June 2017

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Image (top left) by Agnieszka