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Lee, S.,Kim, M. J.,Lee, J.,Park, J.,Kang, S.-H.,Lee, S.-J.,Yun, Y. CARL HANSER VERLAG 2017 MATERIALPRUFUNG Vol.59 No.1
<P>The corrosion behavior of commercially available and welded Haynes (R) 160 (R) Ni-Co-Cr-Si alloy samples was investigated by exposure to coal-gasifying integrated coal gasification combined cycle pilot plant facilities under typical conditions as 2.005 MPa and 160 to 300 degrees C. The morphological and microstructural analyses of the exposed samples were conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis on the external surface of the recovered corrosion test samples to obtain information of the corrosion scale. These analyses based on the pre- and post-exposure corrosion test samples combined with thermodynamic Ellingham-Pourbaix stability diagrams provided preliminary insight into the mechanism of the observed corrosion behavior prevailing in the piping materials that connected the particulate removal unit and the water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material wastage was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested: the observed material waste and corrosion behavior of the Haynes (R) 160 (R) Ni-Co-Cr-Si alloy samples cut off from the coal syngas integrated coal gasification combined cycle plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered. This contribution supplements the already published studies of Haynes (R) 556 (R) Fe-Ni-Cr-Co alloys and Haynes (R) 230 (R) nickel-based superalloys and completes the comprehensive series of such coal-gasifying integrated coal gasification combined cycle pilot plant exposure tests using the facilities affiliated with the Institute for Advanced Engineering.</P>
Lee, Sungkyu,Kim, Min Jung,Park, Joohyun,Hwang, Sang Yeon,Chung, Seok-Woo,Lee, Seung-Jong,Yun, Yongseung Carl Hanser Verlag GMBHCo KG 2018 MATERIALPRUFUNG Vol.60 No.2
<P>A mechanistic exposure experiment was performed on welded samples of the commercially available Haynes (R) Hastelloy (R) C-4 (R) Ni-Cr-Mo-Fe alloy (65 wt.-% Ni, 16 wt.-% Cr, 16 wt.-% Mo, 3 wt.-% Fe, 2 wt.-% Co, 1 wt.-% Mn, 0.7 wt.-% Ti, 0.5 wt.-% Cu, 0.08 wt.-% Si and 0.01 wt.-% C) at coal gasification pilot plant facilities affiliated with the Institute for Advanced Engineering in Yongin-si, South Korea. The alloy samples were preoxidized at 400 degrees C under a stagnant air atmosphere for 24 h prior to exposure to the corrosive environment (60 % CO, 28.4 % H-2, 2.5 % CO2, 0.8 % CH4, 600 ppm H2S and 110 ppm carbonyl sulfide under 2.005 MPa pressure and 170 degrees C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed to provide insight into the mechanism of the observed corrosion behavior prevailing in the piping materials between the particulate removal unit and water scrubber of the coal gasification pilot plant. The thermodynamic inference of the corrosion mechanism was supplemented with morphological, compositional and microstructural analyses of the exposed samples using scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy analyses performed on the external and cross-sectional surfaces of the recovered corrosion test samples to comprehensively examine the corrosion scale. The X-ray diffraction results revealed stable corrosion products of NiO, MoNi4 and Cr4.6MoNi2.1 after a total accumulated exposure duration of 139 h to the corrosive atmosphere. Scanning electron microscopy and energy dispersive X-ray spectroscopy positively identified the formation of rather continuous and adherent preoxidation corrosion products in the alloy samples, although extensively peeled off oxides were eventually observed as corrosion scale on the post-exposure alloy samples, which were attributed to the combined effects of the evaporation of the hydrated Fe, Al and Cr chlorides and their subsequent transformation into thin (spalled) oxides.</P>