Zum Einsatz elektrochemischer und metallographischer Prüfmethoden an korrosiv beanspruchten Bauteilen von Rauchgasentschwefelungsanlagen in Kraftwerken

Apart from the conventional metallographic testing method for assessing corrosion-resistant components in flue gas desulphurisation plants (FGD) an electrochemical investigation method is described. With the aid of mobile metallography it is possible to e.g. assess microscopically a Duplex structure. The electrochemical mobile method also provides additional information on corrosion resistance. Here selected parts of the surface in contact with the medium of the component to be investigated are being examined with the help of an ECMC measuring system, i.e. non-destructive current-potential curves (CPC) are recorded mobile and if necessary the resulting structure is used for analysis. For classification of the components and its surfaces investigated the CPCs are recorded in the areas - 600 mV to + 1500 mV with a period of 10 mV/s. This allows to classify the components in contact with media according to passive or non-passive. If the CPCs achieve very small passive residual current IPR at transpassive breakthrough potential UD of some 800 to 1000 mV, the surface is sufficiently passive. If the transpassive breakthrough potential UD lies between - 400 and + 300 mV, the surface is not sufficiently passive and thus not suited for quencher pumps. A Duplex cast surfaces with spills, occurring during manufacturing, is classified like X20Cr-MoV12-1 boiler tube material and should therefore be ground. It can be shown that the course of the current-potential curve correlates with the structure existing at the measuring point and that this method allows much more precise statements on corrosion resistance as sensitive addition to conventional metallography. In the VGB Instruction Sheet 502, Item 7.3 reference is also made to this method due to its simple application.