Corrosion behavior of welded Ni-Co-Cr-Si alloys during exposure in integrated coal gasification combined cycle syngas plants

Abstract

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.