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Development Of High Velocity Oxygen Fuel (HVOF) Corrosion Resistant Coatings; A Comparison Between Novel High Entropy Alloy (HEA) And Conventional Cermet Coatings For Geothermal Applications

Several components in geothermal power plants need to be protected from the environment due to the corrosive nature of geothermal fluids used to generate the energy. Depending on the fluid properties for any location, the type of protection varies. In geothermal power plants, wear, erosion, corrosion, and scaling are all known problems1. These issues can lead to a variety of outcomes, ranging from decreased plant efficiency to upstream component failure. Failure of a component is thus a significant challenge in the geothermal industry, where materials need to operate in high temperature and high pressure environments. A major cost factor is also linked to the drilling of geothermal wells, where cost rises due to increased depth/distance of drilling, increased trip times, higher high temperature and high-pressure conditions which can lead to increased wear and corrosion of the materials. To address the issue, coatings can be considered to be a potential solution to extend the service life of downhole equipment.

Product Number: 51322-17675-SG
Author: Gifty Oppong Boakye, Baldur Geir Gunnarsson, Erlend Oddvin Straume, Feifei Zhang, Arna María Ormsdóttir, Sigrún Nanna Karlsdóttir
Publication Date: 2022
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Corrosion damage of materials operating in the harsh geothermal environment with corrosive species, high temperatures and pressures necessitate the development of novel, cost-effective corrosion-resistant coatings to extend the service life of down-hole drilling equipment and power plant components. The thermal spraying process is a well-established and versatile method for producing thick coatings in terms of cost, wide range of powder selection, and high deposition efficiency. High Velocity Oxygen Fuel (HVOF) thermal spraying process has proven to be one of the most effective techniques for deposition of conventional cermet-carbide composite coatings improving their high-temperature oxidation corrosion, erosion, and wear resistance. The objective of this work focuses on testing the corrosion resistance of a CoCrFeNiMo0.85 high entropy alloy (HEA) coating fabricated by HVOF technique. Here we report the comparative analysis of corrosion resistance for the developed CoCrFeNiMo0.85 and CrC–NiCr, WC–Co carbide systems. The HEA and Cermets were immersed for 14 days in a simulated alkaline geothermal drilling environment at 120 °C and 50 bar. In addition, an electrochemical-accelerated corrosion test in a 3.5wt% NaCl was carried out at ambient temperature to investigate the behavior of the coatings in the presence of Cl-ions. The compositional effect of the microstructure on corrosion performance of the tested samples is discussed by analyzing corrosion damages and products using SEM/EDS analytical methods. The findings are essential to determine the suitability of HVOF as a fabrication method for CoCrFeNiMo0.85 HEA coatings and the candidacy of the resulting coating for corrosion protection of components used in geothermal energy production.

Corrosion damage of materials operating in the harsh geothermal environment with corrosive species, high temperatures and pressures necessitate the development of novel, cost-effective corrosion-resistant coatings to extend the service life of down-hole drilling equipment and power plant components. The thermal spraying process is a well-established and versatile method for producing thick coatings in terms of cost, wide range of powder selection, and high deposition efficiency. High Velocity Oxygen Fuel (HVOF) thermal spraying process has proven to be one of the most effective techniques for deposition of conventional cermet-carbide composite coatings improving their high-temperature oxidation corrosion, erosion, and wear resistance. The objective of this work focuses on testing the corrosion resistance of a CoCrFeNiMo0.85 high entropy alloy (HEA) coating fabricated by HVOF technique. Here we report the comparative analysis of corrosion resistance for the developed CoCrFeNiMo0.85 and CrC–NiCr, WC–Co carbide systems. The HEA and Cermets were immersed for 14 days in a simulated alkaline geothermal drilling environment at 120 °C and 50 bar. In addition, an electrochemical-accelerated corrosion test in a 3.5wt% NaCl was carried out at ambient temperature to investigate the behavior of the coatings in the presence of Cl-ions. The compositional effect of the microstructure on corrosion performance of the tested samples is discussed by analyzing corrosion damages and products using SEM/EDS analytical methods. The findings are essential to determine the suitability of HVOF as a fabrication method for CoCrFeNiMo0.85 HEA coatings and the candidacy of the resulting coating for corrosion protection of components used in geothermal energy production.

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