Midway evaluation in Mechanical Engineering - Gifty Oppong Boakye
Title: Tribological Properties and Corrosion Behavior of Coatings for Geothermal environment
Doctoral candidate: Gifty Oppong Boakye
Sigrún Nanna Karlsdóttir, Professor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland
Andri Stefansson , Professor at the Faculty of Earth Sciences, University of Iceland
Danyil Kovalov, Researcher at the University of Virginia, USA
The practical service life of most industrial components is limited. The components are inclined to fail or lose their functionality over their lifetime for a variety of reasons which includes component degradation due mechanical loads, wear and corrosion. The economic impact is substantial due to both direct and indirect cost of maintenance, repair, part-replacement, downtime and safety. Methods to reduce the afore-mentioned degradative phenomena have been achieved in various ways. This includes applying coatings which gives the advantage of designing a cost-efficient component of an inexpensive bulk material with a modified top surface. In geothermal power generation, the principal processes related to component degradation are mainly corrosion and mechanical wear and in other cases fatigue due to long service life cycles and the operating environment. Although each process has a large impact on productivity, the combined effect of the corrosion and wear processes is possible particularly because of the high loads, high temperature and pressure in geothermal environment.
The objective of the Ph.D. research project is to investigate the corrosion behavior and tribological properties of novel coatings designed to add the wear and corrosion resistance of the materials currently used in geothermal environment. The goal is to identify whether the coatings have the potential to increase the lifetime of various components used for the utilization of geothermal energy. Several types of novel coatings applied with different coating techniques onto metallic substrates representative of geothermal plant and drilling components are analyzed and tested within the PhD project. The types of coatings include cermet based, graphene oxide based, high entropy alloys (HEA) based and electroless-nickel plating. To achieve the objective of the Ph.D. research the following tasks have been performed: evaluating, testing and analyzing i) the surface characteristics, ii) the tribological properties, and iii) the corrosion behavior of the coatings in simulated geothermal environment. From the preliminary results coatings have been identified that can act as a physical barrier to prevent metal dissolution (corrosion) and increase wear resistance. Also, it has been shown the hardness may directly influence abrasion and wear, but the surface roughness complicates sliding behavior. However, deviations were dependent on resulting microstructure of some the coatings and the chemistry (Cl-, H2S, CO2) of the test environment promoting localized corrosion. Lastly, a secondary hydrophobic property of some of the engineered coatings improved wetting properties which minimizes solids or scale deposition.
The results of the Ph.D. research will make it possible to identify the best materials and deposition techniques for coating systems that result in high corrosion and wear resistance coatings. The coatings can be successfully incorporated in novel drilling equipment and in early project phases in the construction of geothermal plants. This can reduce direct and indirect cost of maintenance, repair, part-replacement, downtime and safety energy in the production of geothermal energy.