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P. Linhardt:
"MIC in Hydroelectric Power Plants and Approaches for Risk Assessment";
Hauptvortrag: EUROCORR 2013, Porto/PT (eingeladen); 01.09.2013 - 05.09.2013; in: "EUROCORR 2013", (2013), Paper-Nr. 1279, 5 S.

Historically, hydro power is one of the oldest approaches to make use of renewable energy sources. There exists a long term experience on the corrosion behaviour of the metallic materials which are in use for the components in direct contact with water. Consequently, cases of corrosion of the blank turbine components are rather rare.

However, from time to time, corrosion cases are observed with the today´s standard material in this kind of application, the martensitic stainless steels mat. no. 1.4313 and 1.4317, i.e. the iron based alloy Cr13Ni4. Although the chloride content of the water is below the traditional design limits (ca. 100-150 mg/L) in such cases, pitting corrosion is observed. Chloride induced pitting is caused by biomineralized manganese dioxide which leads to ennoblement of the steel and possibly to potentials exceeding the critical pitting potential. This mechanism is established in the literature [1] and may be designated as microbially infuenced corrosion by manganese oxidizing microorganisms (MIC by MOMOs). To the author´s knowledge, such cases in hydro power plants (HPPs) were, up to now, related to new Kaplan type turbines in lowland rivers.

For designers of HPPs it is of great interest to have a guideline for risk assessment for this kind of MIC. Based on the experiences gained from several failure cases, and from corrosion tests carried out on original components, the following parameters were derived and will be discussed:

. surface state of components.
. data on water chemistry: chloride, manganese, organic carbon, alkalinity.
. microbiological testing for MOMOs.
. regime of operation.

For the case of HPP refurbishment projects, the options to gain information from the existing HPP will be highlighted by an example. Finally, the possible countermeasures for HPP projects with a certain risk of MIC by MOMOs will be discussed briefly.

corrosion, hydroelectric power plants, microbially influenced corrosion, stainless steel