engleski

Different corrosion behaviour of CuNi10Fe1Mn alloy condenser tubes in seawater

Two CuNi10Fe1Mn condenser tube samples from boat heat exchangers were investigated due to their different corrosion behaviour in exploitation. One tube was in exploitation nearly 20 years before significant corrosion damage occurred (sample 1), while second tube of different manufacturer showed corrosion damages in 2 months of exploitation (sample 2). In its working conditions seawater was passing through the pipes and R407C gas around the pipes. Chemical analysis, microstructural and hardness investigations and laboratory electrochemical investigations of corrosion behaviour of samples in sea water were performed in order to determine the main reason for different durability of condenser tubes. After electrochemical investigations the polarization surface damage was verified by SEM analysis. Both samples belong to the CuNi10Fe1Mn alloy system with the significant difference in the mass fraction of iron content (around 30% higher for sample 1). Samples coincide in the structural sense (type and size of grain) and in mechanical properties (hardness of 133 HV1). Fe content in the CuNi10Fe1Mn alloy has the key role in the corrosion behaviour of the tested samples. It has been found that (regardless of the temperature of the heat exchanger) the corrosion resistance of the tested samples increases with increasing Fe content in the alloy. Namely, the corrosion current decreases in same order, while the polarization resistance and properties of surface oxide layer increase. SEM analysis confirmed less damage on the surface of samples with higher Fe content.

CuNi10Fe1Mn ; Corrosion ; Microstructure ; Polarization ; SEM/EDS analysis

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