Abstract
The corrosion behaviour of a new titanium-based alloy, with nickel, molybdenum and zirconium as the main alloying elements, was studied in a simulated geothermal environment at various phase conditions of a corrosive fluid. Corrosion testing of carbon steel was also conducted for comparison. Both materials were tested at an elevated temperature between 180 and 350 °C and at a 10 bar gauge pressure in H2O containing HCl, H2S, and CO2 gases with an acidic condensate of pH = 3. The study found that the titanium alloy demonstrated good corrosion resistance in a single- and multiphase geothermal environment. In the testing volume, where the boiling of testing fluid occurred, the carbon steel was prone to localized damage of oxide, sulphide and chloride corrosion products. In the superheated testing volume, a homogeneous oxide corrosion layer was observed on the carbon steel. In the testing volume where condensation of the testing fluid occurred, a sulphide layer with an oxide sublayer was formed on the carbon steel.
Highlights
The application of titanium and titanium-based alloys as a structural and process equipment material in the geothermal industry has received growing attention in the last few decades due to its excellent corrosion resistance, which exceeds that of the more conventional steels and stainless steels [1]
Increased corrosion resistance and mechanical strength at high temperatures are required if a titanium alloy is to be used in a geothermal environment
From the corrosion testing of the carbon steel, it was concluded that the testing fluid was at boiling conditions at the first few centimetres of reactor
Summary
The application of titanium and titanium-based alloys as a structural and process equipment material in the geothermal industry has received growing attention in the last few decades due to its excellent corrosion resistance, which exceeds that of the more conventional steels and stainless steels [1]. Schutz et al [7] reported that nickel and molybdenum are thought to enhance the corrosion resistance of the TiO2 passive film and increase the mechanical strength of the titanium alloy at high temperatures. Zirconium has been reported to enhance the mechanical stability of β-phase (body centred cubic (BCC)) titanium in a Nb- and Zr-based alloy [8,9,10] and enhance the passivity and corrosion resistance [11] (up to 50 wt.% Zr) of titanium alloys for biomedical applications. Increased corrosion resistance and mechanical strength at high temperatures are required if a titanium alloy is to be used in a geothermal environment. The corrosion behaviour of a new titanium-based alloy (with nickel, molybdenum and zirconium as the main alloying elements), will be studied in a simulated geothermal environment at various phase conditions of the corrosive fluid from 180 to 350 ◦C at 10 bar gauge
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