A study on the erosion-corrosion behaviour of engineering materials used in the geothermal industry

Abstract

Erosion-corrosion can be a significant issue for engineering components used in the geothermal industry. This study assesses the erosion-corrosion behaviour of a wide range of engineering alloys which are used in various parts of geothermal power plants. The evaluated materials comprised a carbon steel, low-alloy steel, three grades of stainless steel together with Ni–Cr alloy (Inconel 625) and Ti–6Al–4V. Tests were conducted by utilising a submerged 90° impinging slurry jet consisting of silica sand particles suspended in an acidic (pH 4) aqueous solution consisting of 3.5% NaCl. Gravimetric mass losses, in-situ potentiodynamic polarisation scans and an enhanced volumetric analysis technique were used to assess the influence of hydrodynamic conditions on the erosion-corrosion behaviour of the test materials. The effect of applied cathodic protection was also examined. Post-test metallurgical examination was also conducted via SEM. The results showed the distinct differences between low alloy steels and “corrosion resistant” alloys – with the former demonstrating substantial material loss in the low-angle corrosive wear region due to large amounts of corrosion-related damage. Both superaustenitic stainless steel (UNS S31254) and Inconel 625 (UNS N06625) exhibited the greatest erosion-corrosion resistance of the test materials – with Inconel 625 demonstrating the greatest resistance to high angle corrosive wear. The relevance of the findings to materials selection and other methods of protection against surface degradation in geothermal power plants is discussed.