This study aims to evaluate the influence of heat input and dilution on the corrosion behaviour of a weld overlay coating of Inconel 625 deposited using a plasma transferred arc process. Cyclic potentiodynamic polarisation, double-loop electrochemical potentiometric reactivation and critical pitting temperature (CPT) experiments were performed to determine sensitisation and pitting corrosion resistance of the coating, besides microstructural characterisation and microhardness testing. The overlay showed to be resistant to sensitisation in all cases. Within the scope of this study, only the CPT test was able to cause pitting in the alloy, which showed that increments of the specimen's chemical dilution and heat input induced a lower CPT. This is mainly due to different chemical compositions among the distinct phases present in the coating.
In thermal and nuclear power plants, numerous corrosion phenomena observed in copper alloy condenser tube nests have been identified by means of metallography. Particular importance has been given in the paper to verification of secondary dezincification, initiated at the boundaries of the α‐grains in copper tubes. Typical phenomena of corrosion under stress and of erosion‐corrosion have been observed in other copper alloy tube nests, with circulation of sea and river water. In some instances a semi‐quantitative check of the phenomenon on the whole tube nest, by means of eddy currents, has been made possible through the simultaneous application of metallographic analysis.
This paper resumés some of the main findings and conclusions of a study group on cooling water problems (1) set up by UNIPEDE (2). The paper represents only the personal point of view of the author, in particular as chairman of the above mentioned group. The basic aim of the work was the study of the effects of the discharge of cooling water in the receiving water bodies (rivers, lakes and coastal waters). This type of assessment permits a more balanced and pragmatic approach to aspects such as thermal pollution, entrainment, impingement and pollution by antifouling agents.
The first part of the paper deals with the problem of damage to organisms entering a cooling system. An important factor in assessing the meaning of such aspect is the growing evidence that there is no reduction in fish population of the receiving water body associated with the operation of modern power plants despite the catch in the once through-cooling systems due to entrainment and impingement, that can be minimized, but not avoided.
The second part deals with the different methods of fouling prevention in power plants, with their possible environmental effects in the receiving water bodies.
The third part is a comprehensive review of the results of aquatic impact studies at power plants, that is the results of many experimental investigations carried out in the field to evaluate the effects of the operation of once through cooling systems sited on rivers, lakes, or coastal waters.
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