Erosion and Corrosion Resistance Performance of Laser Metal Deposited High-Entropy Alloy Coatings at Hellisheidi Geothermal Site.

Andri Isak Thorhallsson,Svava Davidsdottir,Shiladitya Paul,Emily Davison,Francesco Fanicchia,Dagur Ingi Olafsson

doi:10.3390/ma14113071

Abstract

Geothermal process equipment and accessories are usually manufactured from low-alloy steels which offer affordability but increase the susceptibility of the materials to corrosion. Applying erosion-corrosion-resistant coatings to these components could represent an economical solution to the problem. In this work, testing of two newly developed laser metal deposited high-entropy alloy (LMD-HEA) coatings—CoCrFeNiMo0.85 and Al0.5CoCrFeNi, applied to carbon and stainless steels—was carried out at the Hellisheidi geothermal power plant. Tests in three different geothermal environments were performed at the Hellisheidi site: wellhead test at 194 °C and 14 bar, erosion test at 198 °C and 15 bar, and aerated test at 90 °C and 1 bar. Post-test microstructural characterization was performed via Scanning Eletron Microscope (SEM), Back-Scattered Electrons analysis (BSE), Energy Dispersive X-ray Spectroscopy (EDS), optical microscopy, and optical profilometry while erosion assessment was carried out using an image and chemical analysis. Both the CoCrFeNiMo0.85 and Al0.5CoCrFeNi coatings showed manufacturing defects (cracks) and were prone to corrosion damage. Results show that damage in the CoCrFeNiMo0.85-coated carbon steel can be induced by manufacturing defects in the coating. This was further confirmed by the excellent corrosion resistance performance of the CoCrFeNiMo0.85 coating deposited onto stainless steel, where no manufacturing cracks were observed.

Highlights

Published: 4 June 2021In geothermal power production, hot geothermal fluid from the earth’s crust is discharged from several or dozen wells where the geothermal energy from the fluid is utilized in steam turbines to produce mechanical and eventually electrical energy as a final energy product
Hot geothermal fluid from the earth’s crust is discharged from several or dozen wells where the geothermal energy from the fluid is utilized in steam turbines to produce mechanical and eventually electrical energy as a final energy product
During the processing of geothermal fluid from the initial to the final processing steps, the fluid flows through various equipment, including casing, piping, bends, valve housings, separators, heat exchangers, turbine blades, etc

Summary

Introduction

Hot geothermal fluid from the earth’s crust is discharged from several or dozen wells where the geothermal energy from the fluid is utilized in steam turbines to produce mechanical and eventually electrical energy as a final energy product. During the processing of geothermal fluid from the initial to the final processing steps, the fluid flows through various equipment, including casing, piping, bends, valve housings, separators, heat exchangers, turbine blades, etc. The extent of corrosivity of a geothermal environment can vary between geothermal systems due to significant variations in their thermodynamic and chemical properties [1]. The erosive and corrosive impact on the material depends on the fluid temperature, chemical composition, velocity, phase state of the geothermal fluid, the extent of scaling on the material surface, susceptibility of the material, etc. Previous corrosion performance studies of materials have reported corrosion and erosion-corrosion behaviors in tests that were conducted in both in situ geothermal environments [3,4,5,6] and simulated geothermal

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Conclusion