Development of Corrosion Resistant Alloys for Municipal Waste Incinerators

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Corrosion performance of eighteen commercial and thirteen lab-melted alloys have been evaluated in three different molten salts in the temperature range 723 to 873K in order to select materials to be employed in municipal waste incinerator environments. The evaluation was performed using an AC impedance screening test which was developed in this study as an instrument for rapid evaluation of hot corrosion. The most promising candidate alloys have been selected in each melt, and subsequently evaluated in a conventional salt coating test. The corrosion data obtained in AC impedance screening tests has been analyzed by a multiple linear regression method in order to clarify the effect of alloy elements on the corrosion performance.From the AC impedance corrosion screening test and salt coating tests of thirty one alloys in the sulfate, the chloride and the chloride/sulfate environments, the following results were drawn :1.In the chloride containing environments, high Cr and high Mo alloys indicated excellent corrosion performance, while in the sulfate environment, high Cr and Mo-free alloys showed excellent corrosion resistance.2.Alloy 625 and Alloy C-22 were selected as most excellent corrosion resistant materials in the simulated municipal waste incinerator environments.3.Poor corrosion resistant alloys tend to show an acceleration of corrosion rate with an increase in water content in both the sulfate and chloride melts. Meanwhile, it seems that an increase of water content reduced the corrosion rates in the sulfate/chloride melt. In general, a change in the water content provided no significant difference in the rankings of corrosion performance of the alloys in the employed melts.4.The results obtained from AC impedance testing were in good agreement with those from conventional salt coating test. The electrochemical screening test system developed in this study was found to be very useful as a rapid evaluation method for molten salt corrosions.