Nickel based coatings used for erosion-corrosion protection in a geothermal environment

Abstract

Development of advanced coatings for corrosion protection for different technological application currently has a strong emphasis worldwide. Nickel alloy based coatings have for example been tested and studied for oil and gas industry application, but not so much for geothermal industry. This paper aims to reveal a study on the potential application of Nickel chromium-based coating, high-velocity oxygen fuel (HVOF) sprayed, for geothermal power plants components for corrosion-erosion and wear protection. Various tests and analysis were performed to assess the suitability of the coating for the geothermal environment. Microstructure and chemical composition of the coating was analyzed by optical and Secondary Electron Microscope (SEM) equipped Energy Dispersive X-Ray Spectroscopy (EDS). The mechanical properties of the coatings were evaluated through nano-indentation and adhesion tests. Hardness test of the coating was measured with a Vickers hardness tester, using 200 g load. The hardness value of the coating was high in comparison with the reference sample. Wear tests revealed that the sprayed layer had good adhesion and cohesion, and that the wear resistance improved by 12% compared to the reference sample. The samples were exposed to geothermal steam for thirty days to test the erosion-corrosion resistance. The coating was investigated before and after the corrosion test with visual, optical and electron microscopic analysis to investigate the corrosive effect of the geothermal steam. The results from the EDS analysis showed evidence of some minor erosion-corrosion damages at the surface of the coating as well as delamination and cracking of the coating.