51315-5857-A Study of the Behavior of Several High-Chromium Nickel Alloys Under Conditions Conducive to Metal Dusting

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Product Number: 51315-5857-SG

ISBN: 5857 2015 CP

Author: Vinay Deodeshmukh

Publication Date: 2015

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~~Several nickel alloys containing high chromium contents and other elements known to enhance resistance to metal dusting were tested in a flowing gas mixture of 68% CO + 26% H2 + 6% H2O at 680oC. The onset of the metal dusting reaction was accelerated by using temperature cycling conditions to shorten the life of otherwise protective oxide scales. Each cycle consisted of 45 min. at a temperature of 680°C and a cooling period of 15 min. during which the alloy specimens rapidly reached a temperature of about 90°C. The cycling process was interrupted at intervals and the alloys removed for examination and weighing. The total duration of the test was 1200 cycles.All the test alloys developed chromia scales. Nonetheless they all dusted to some extent under these extreme conditions developing filamentary carbon deposits decorated with metal nanoparticles. However differences were recorded in the number of cycles required to initiate coking hence surface damage and in the weight changes versus the number of cycles. A shallow subsurface alloy zone formed very fine carbide precipitates showing that the protective value of the surface chromia scale had been diminished. An alloy containing only 22 wt % Cr dusted severely and developed a thick carbon deposit (coke) on its surface. All other alloys experienced net total weight uptakes in 1200 h of ? 0.3 mg cm-2. Because weight losses were caused by scale spallation and coke detachment measured weight changes did not correspond simply to the extent of attack. Thus in order to compare and rank these metal dusting resistant alloys time to initiate catalytic coke or dusting reaction was considered.The metal dusting tests were augmented by optical and SEM/EDS analyses of the surfaces and cross-sections. The differences in behavior between the various test alloys enabled some correlation with composition.