Feasibility Study of High-Velocity Oxy-fuel (HVOF) Sprayed Cermet and Alloy Coatings for Geothermal Applications

Abstract Geothermal is one of the least utilized renewable energy sources due to high investment costs and long development cycle. A major cost for geothermal operations is drilling, where the cost is dependent on drilling depth, tripping times, environments, etc. These costs can increase significantly for greater drilling depths, harsher environments, component failures, etc. During drilling, hammers break the rock through repetitive impact and cuttings are removed via a high-velocity stream. Component lifetime can be extended by selecting appropriate coatings resulting in reduced lost time and improved drilling efficiency. High-velocity oxygen fuel (HVOF) spraying is one of the most popular technique to deposit thick, dense and highly adherent coatings. This paper discusses the characteristics of cermet and alloy coatings using liquid-fueled HVOF spraying technique and their performance in simulated geothermal drilling environment. Properties of the deposited cermet (WC-CoCr, CrC-NiCr) and alloy (Ni self-fluxing, Fe-based amorphous) coatings in terms of surface roughness, thickness, porosity, hardness, adhesion strength, and erosion–corrosion resistance have been studied, and their performance are compared with selected benchmarking steel used in geothermal drilling. Based on the findings of this study, recommendations are made on the type of HVOF coatings that can potentially be used in geothermal applications.